The initial prenatal assessment and routine prenatal care

INTRODUCTION — The major goal of prenatal care is to ensure the birth of a healthy baby with minimal risk for the mother. There are several components involved in achieving this objective: Early, accurate estimation of gestational age Identification of the patient at risk for complications Ongoing evaluation of the health status of both mother and fetus Anticipation of problems and intervention, if possible, to prevent or minimize morbidity Patient education and communication

The percentage of pregnant women who initiate prenatal care in the first trimester is one of the standard clinical performance measures used to assess the quality of maternal health care. In the United States in 2006, 83 percent of pregnant women obtained prenatal care in the first trimester, but 3.6 percent received no care or initiated prenatal care in the third trimester [1] .

The optimal components of prenatal care have not been rigorously examined in randomized trials [2-6] . A systematic review of observational studies and randomized trials concluded that there was no conclusive evidence that prenatal care improved birth outcomes [2,4] . Randomized trials have also shown that enhanced prenatal care (eg, extra visits, health education, home visits, telephone contact, psychosocial support) did not result in improved outcomes compared to routine prenatal care [7,8] . However, a randomized trial in young women of low socioeconomic status demonstrated that group prenatal care had a significant reduction in preterm birth, as well as increased patient satisfaction and knowledge of labor, delivery, and infant care [9] .

Further, comparison of pregnancy outcomes in women who receive and do not receive prenatal care is consistently confounded by socioeconomic and other factors that influence access to prenatal care and maternal/perinatal outcome. In the developing world, if prenatal care is not readily available, then adequate delivery of other health care and social services often also are not readily available. This is important since complications resulting in serious morbidity or mortality are most likely to occur at delivery.

Additionally, prenatal care is not a single intervention, instead it represents a series of assessments and interventions over time that are not uniformly applied by different practitioners. Thus, although the "quantity" of prenatal care is relatively easy to measure (ie, timing and number of visits adjusted for gestational age at delivery), the "quality" of prenatal care and the effect of individual components on outcome are quite difficult to measure.

Defining outcomes is also not straightforward as pregnancy has several measurable maternal, fetal, and neonatal outcomes. Lastly, most studies do not possess the sample size necessary to detect statistically significant differences in the outcomes evaluated.

The following discussion relates primarily to prenatal care in the United States. Many of these issues are common to pregnancies worldwide. However, some issues that are highly important in other parts of the world, such as tetanus and malaria prophylaxis, are not discussed here, but are reviewed in detail separately. (See "Overview of malaria in pregnancy" and see "Tetanus").

CARE PROVIDER — In the United States, midwives are the lead maternity care providers for 8 to 9 percent of women during pregnancy and childbirth, family physicians are the lead maternity care providers for 6 to 7 percent of women, and obstetrician-gynecologists care for most of the remainder [34] . The different types of prenatal care providers have been studied: A systematic review evaluated three randomized trials of midwife/general practitioner-managed care compared to obstetrician/gynecologist-led shared care of low risk women [3] . The clinical efficacy of the two groups was similar; however, women favored midwife-led care and, in some countries, there was a cost reduction if antenatal care was provided by staff other than an obstetrician/gynecologist. Another systematic review compared clinical trials of midwife-led antepartum/intrapartum care with other models of care and also found several benefits to midwife-led care (eg, more natural childbirths); perinatal mortality was similar for both groups [10] .

HISTORY AND PHYSICAL EXAMINATION — It is important to identify women at increased risk of maternal medical complications, pregnancy complications, or fetal abnormalities. Early identification of these women gives the provider an opportunity to discuss these issues and their management with the patient and, in some cases, interventions are possible that minimize the risk of an adverse outcome. Ideally, this process is initiated prior to pregnancy during a preconception consultation [11] . (See "Preconception evaluation and counseling").

History — At or prior to the first prenatal visit, the patient should complete a questionnaire detailing her social, medical, and family history. This information can be used to start an obstetrical record that will record her prenatal, intrapartum, and postpartum course. Several paper and computerized obstetrical record forms are commercially available for this purpose. They help to ensure complete and systematic documentation of the pregnancy and often may be used for risk-assessment planning.

The elements of the patient history include: Personal and demographic information (show table 1) Past obstetrical history (show table 2) Personal and family medical history (show table 3) Past surgical history Genetic history (show table 4) Menstrual and gynecological history (show table 5) Current pregnancy history (show table 6) Psychosocial information

The American College of Obstetricians and Gynecologists (ACOG) and the American Medical Association guidelines on domestic violence recommend that physicians routinely assess all pregnant women for domestic violence [12,13] . The clinician should be aware of markers and characteristics of abuse, such as bruising, improbable injury, depression, late prenatal care (presentation after the first trimester), missed prenatal visits,

and appointments cancelled on short notice. (See "Diagnosing, screening, and counseling for domestic violence").

Additional psychosocial issues that should also be assessed include: whether the pregnancy was planned or unintended, potential barriers to care (eg, communication, transportation, child care issues, economic constraints, work schedule), whether the patient has stable housing, her mental health and level of stress, and any use of tobacco, alcohol, or recreational drugs [14] . Areas of concern should be identified and discussed with the patient. This is an opportunity to provide information and, if indicated, make suggestions for possible changes or referral.

After obtaining a complete history, a "problem list" is generated. These lists are useful for preventing the inadvertent omission of necessary maternal or fetal monitoring and interventions.

Estimated date of delivery — A tentative estimated date of delivery (EDD) is calculated from the menstrual history by adding seven days to the first day of the last menstrual period (LMP) and then subtracting three months (in women with 28 day cycles). As an example, if the last menstrual period is February 20, then the EDD will be November 27. If the last menstrual period is May 28, the EDD will be March 4.

Accurate dating is crucial for managing the pregnancy, especially with regard to timing interventions and monitoring fetal growth. Sonographic estimation of the EDD is mandatory when menses are irregular, the LMP is unknown, or in patients conceiving while taking oral contraceptive pills. Routine use of this test appears to be useful in the general obstetrical population, as well (see "Ultrasound examination" below).

Physical examination — A complete physical examination should be performed, with special attention to uterine size and shape and evaluation of the adnexae. Experienced examiners can detect a very contracted pelvis, but clinical pelvimetry is not sufficiently reliable to identify women likely to experience labor abnormalities [3] . Baseline blood pressure, weight, and height should be recorded as part of the examination. Calculating body mass index (BMI) helps to identify at risk populations and enables counseling of the amount of appropriate weight gain in pregnancy. (See "Weight gain in pregnancy").

Sonographic estimation of the EDD is also useful when there is a history of irregular menstrual cycles or when the uterine size estimated on physical examination differs from that predicted by menstrual dating. Some causes for a discrepancy between the actual uterine size and that expected by LMP include uterine fibroids, uterine malposition (eg, retroverted uterus), and multiple gestation. (See "Prenatal assessment of gestational age", section on Clinical assessment).

Sonography is also useful for evaluating suspected adnexal masses and uterine fibroids. (See "Overview of the evaluation and management of adnexal masses" and see "Epidemiology, clinical manifestations, diagnosis, and natural history of uterine leiomyomas").

In a viable pregnancy, the fetal heart usually can be heard by 9 to 12 weeks of gestation using a Doppler instrument. Transvaginal ultrasound can visualize fetal cardiac motion as early as 5.5 to 6.0 weeks.

LABORATORY TESTS — In the absence of diagnostic physical findings, suspected pregnancy should be confirmed by laboratory evaluation. The standard test is the detection of the beta-subunit of human chorionic gonadotropin (hCG) in blood or urine. (See "Diagnosis and clinical manifestations of early pregnancy").

Routine — A standard panel of laboratory tests should be obtained on every pregnant woman at the first prenatal visit. This panel can be augmented by additional testing of women at risk for specific conditions (see "At-risk women" below). Repetition of tests performed preconceptionally is unnecessary. The standard panel typically consists of: Rhesus type and antibody screen to detect antibodies potentially causing hemolytic disease of the newborn. Rh(D)-negative women should receive anti(D)-immune globulin, as indicated. (See "Significance of minor red blood cell antibodies during pregnancy" and see "Pathogenesis and prenatal diagnosis of Rhesus (Rh) alloimmunization" and see "Prevention of Rh(D) alloimmunization"). Hematocrit or hemoglobin and mean corpuscular volume (MCV) to detect anemia and to screen for thalassemia [15] . (See "Nutrition in pregnancy", section on Iron). Cervical cytology. However, pregnancy is not an indication for a change in the frequency of cervical cancer screening. (See "Screening for cervical cancer"). Rubella immunity testing. If nonimmune, the patient should be counseled and receive postpartum immunization. Once documentation of immunity to rubella as a result of infection or immunization has been obtained, repeat testing is unnecessary. (See "Rubella in pregnancy") Urinary infection testing, given pregnant women with untreated asymptomatic bacteriuria are at high risk of developing pyelonephritis. (See "Urinary tract infections and asymptomatic bacteriuria in pregnancy"). Syphilis testing to prevent perinatal transmission. (See "Syphilis in pregnancy"). Hepatitis B antigen testing to prevent perinatal transmission [36,35] . (See "Epidemiology; transmission and prevention of hepatitis B virus infection", section on Perinatal transmission). Chlamydia testing. The Centers for Disease Control (CDC) recommend chlamydia screening for all pregnant women, whereas ACOG's Guidelines for Perinatal Care recommends testing only women at high risk (eg, new or more than one sexual partner, age less than 25 years, history of sexually transmitted diseases, inconsistent condom use, drug use) [16,17] . The US Preventive Services Task Force (USPSTF) recommends limiting screening to women who are 24 years or younger and older women who are at increased risk. The National Screening Committee in the United Kingdom also does not recommend routinely screening all pregnant women [18] .

A nucleic acid amplification test (NAAT) of an endocervical specimen is the most sensitive diagnostic test available and also has excellent specificity. Positive tests should be treated. (See "Genital Chlamydia trachomatis infections in women" and See "Screening for Chlamydia trachomatis", sections on Pregnancy and see "Chlamydia trachomatis infections in the newborn"). Thyroid function. Neurologic development may be adversely affected in children born to mothers with hypothyroidism, while maternal

hyperthyroidism can lead to fetal and maternal complications [19,20] . (See "Treatment and prognosis of congenital hypothyroidism" and see "Overview of thyroid disease in pregnancy").

Professional societies (eg, ACOG [21] , Endocrine Society [22] ) have recommended testing pregnant women for thyroid dysfunction only if they are symptomatic or have a personal or family history of thyroid disease or a medical condition associated with thyroid dysfunction (eg, diabetes mellitus). Some data suggest that this approach may miss up to one-third of women with hypothyroidism [23] . For this reason, some experts recommend universal screening for thyroid dysfunction in pregnant women or those attempting to become pregnant [24] . However, the clinical implications of failing to diagnosis women with subclinical hypothyroidism are unclear. (See "Overview of thyroid disease in pregnancy", section on Screening).

Human immunodeficiency virus — ACOG supports universal HIV testing of pregnant women early in each pregnancy using an 'opt-out' approach [25] . Advantages of universal testing include: An informed decision can be made about continuing the pregnancy Appropriate medical management of the woman herself can be initiated Counseling for prevention of transmission to or identification of infected partners In the absence of intervention, the risk of perinatal transmission is from 15 to 40 percent and can be reduced to less than 2 percent with antiretroviral therapy and avoidance of breastfeeding and labor [17] .

The benefit of the 'opt-out' approach over the 'opt-in' approach was illustrated in a study that found an opt-in policy was associated with testing rates of only 50 to 60 percent in some Canadian provinces due to patient refusal and physician failure to offer the test [26] . On the other hand, those provinces that chose an opt-out approach achieved high rates of testing, 95 to 100 percent. Similar success with the opt-out approach has been described in the United States [27] .

In some areas, local law requires that patient notification, as well as a signed consent form indicating permission for HIV testing, be obtained. The medical record should document the patient's decision to accept or decline testing. Reasons for refusal should be explored and testing offered at another time [17] .

Retesting in the third trimester (≤ 36 weeks of gestation) is recommended for women at increased risk for acquiring HIV infection, in areas of high HIV prevalence, and for women who declined testing earlier in pregnancy [25] . The basis of this recommendation is that appropriate intervention peripartum can significantly reduce perinatal transmission. A conventional or rapid test can be used in the third trimester. (See "Diagnostic assays for HIV infection" and see "Counseling and obstetrical management of the HIV-infected woman to reduce perinatal HIV transmission").

Risk factors for acquiring HIV and serologic testing are discussed in detail separately. (See "Screening for sexually transmitted diseases").

Down syndrome screening — Down syndrome is the most common chromosome abnormality among live born infants. All pregnant women should be offered Down syndrome screening. While such screening can be performed in the first or second trimester or both, first trimester screening test characteristics are better than those in the second trimester only. (See "Overview of prenatal screening and diagnosis of Down syndrome").

At-risk women — Additional laboratory tests commonly performed in at-risk individuals are listed below. The health care provider should interpret the test results for the patient and discuss options for further evaluation or management. If a disorder is diagnosed, then the natural history of the disorder, risk of disease in offspring, and the woman's reproductive options should be discussed [28] . An abnormal result suggesting the presence of a heritable disorder is often an indication for referral for genetic counseling.

Testing for infection N. gonorrhea — In epidemiologic studies, risk factors for acquisition of STDs include young age (15 to 24 years old), African-American race, unmarried status, geographical residence in an area of high prevalence, new sex partner in past 60 days, multiple sexual partners, history of a prior STD, illicit drug use, and admission to correctional facility or juvenile detention center. Testing and management of positive test results is reviewed separately. (See "Neisseria gonorrhoeae infections in women" and see "Gonococcal infection in the newborn"). Tuberculosis — All pregnant women from populations that are recommended to have tuberculosis screening should have a skin test placed. At-risk populations, procedure for and interpretation of skin testing, and management of women with positive test results are described separately. (See "Diagnosis of latent tuberculosis infection in adults" and see "Tuberculosis in pregnancy"). Toxoplasmosis — The two most common means of acquisition of toxoplasmosis are via environmental exposure (contaminated cat litter boxes or soil) and ingestion of undercooked meat from infected animals. Whether all pregnant women should undergo serological screening for toxoplasmosis is controversial. It is a routine practice in some areas of relatively high prevalence, such as France. (See "Toxoplasmosis and pregnancy") Hepatitis C antibodies — Several organizations have provided guidelines for who should be tested. Despite having reviewed similar data and including experts, the various guidelines do not all agree, except that pregnancy alone is not an indication for testing. A summary of recommendations from the major organizations can be found separately. (See "Screening for and diagnostic approach to hepatitis C virus infection"). Varicella — All pregnant women should be assessed for immunity to varicella. Women without evidence of immunity to varicella should avoid exposure to individuals with varicella, may be candidates for passive immunization with variZIG during pregnancy, and are candidates for varicella vaccine postpartum [29] . (See "Varicella-zoster virus infection in pregnancy"). Bacterial vaginosis — Screening for bacterial vaginosis is not recommended as a routine component of prenatal care. Whether asymptomatic women with a history of prior preterm birth should be screened and treated, if positive, to lower the risk of recurrent preterm birth is controversial. (See "Diagnostic approach to women with vaginal discharge or vulvovaginal symptoms", section on Bacterial vaginosis). Herpes simplex virus — Routine screening for herpes simplex virus (HSV) infection in asymptomatic women is generally not recommended,

but this is controversial [30] . Type-specific screening may be reasonable in asymptomatic partners of symptomatic men [31] . (See "Genital herpes simplex virus infection and pregnancy").

Testing for heritable disorders Red cell indices — Thalassemias occur in higher frequency in the Mediterranean area, the Middle East, Southeast Asia, Africa, and the Indian subcontinent. An MCV less than 80 femtoliters (fL) in the absence of iron deficiency denotes patients at risk for alpha or beta thalassemia. A detailed description of patients and risk, and interpretation and management of positive test results can be found separately. (See "Prenatal testing for the hemoglobinopathies and thalassemias") Hemoglobin electrophoresis — The structural hemoglobin variants S and C are most common in tropical Africa but are found in the Mediterranean area, Saudi Arabia, and Caribbean. Hemoglobin E is noted among Southeast Asians and may be the most common structural hemoglobin disorder in the world. A detailed description of patients and risk, and interpretation and management of positive test results can be found separately. (See "Prenatal testing for the hemoglobinopathies and thalassemias") Patients who are of Eastern European or Ashkenazi Jewish descent or who have a relative with one of the genetic conditions prevalent in the Ashkenazi Jewish population should be offered carrier screening. One of these disorders, Tay-Sachs disease, also has a higher prevalence in individuals of Pennsylvania Dutch, Southern Louisiana Cajun, and Eastern Quebec French Canadian descent. The diseases for which these individuals are at risk and issues regarding screening are discussed in detail separately. (See "Prenatal screening for genetic disease in the Ashkenazi Jewish population"). Cystic fibrosis — Information about cystic fibrosis screening should be available to all couples. Cystic fibrosis carrier screening especially should be offered to couples who are at increased risk because of Caucasian, European, or Ashkenazi Jewish ancestry. Cystic fibrosis counseling and carrier testing are discussed in detail separately. (See "Cystic fibrosis: Prenatal genetic screening"). Serum phenylalanine level — Elevated serum phenylalanine concentration during early pregnancy in a mother with phenylketonuria or hyperphenylalanemia can result in phenylalanine embryopathy, which can be prevented by dietary restriction of phenylalanine intake. (See "Overview of phenylketonuria"). Fragile X — The population at risk includes, but is not limited to, individuals of either sex with intellectual disability, developmental delay, or autism. (See "Prenatal screening and diagnosis for fragile X syndrome", section on Candidates for screening).

Other potentially useful tests

Ultrasound examination — Randomized trials have shown that routine early ultrasound examination is beneficial in an unselected population because of better estimation of gestational age resulting in significantly reduced frequency of labor induction for postterm pregnancy and use of tocolysis for suspected preterm labor. (See "Routine prenatal ultrasonography as a screening tool" and see "Prenatal assessment of gestational age").

First trimester ultrasound examination can lead to earlier detection of clinically unsuspected fetal malformations (including aneuploidies) and earlier detection of

multiple pregnancy. These effects have not been proven to improve overall fetal outcome, although studies have lacked power to assess for secondary outcomes. (See "Routine prenatal ultrasonography as a screening tool").

PATIENT EDUCATION — The first prenatal visit is an appropriate time to discuss the patient's responsibilities and the expected course of pregnancy and delivery. This information can be provided by the physician, as well as by ancillary staff, and through written patient handouts. Some of the information should be repeated when the issues become more germane over the course of pregnancy.

The patient's expectations should be oriented to the course of the average pregnancy. A more detailed discussion of the management plan should be communicated with women who are at risk for pregnancy complications because of a maternal disorder or prior adverse pregnancy outcome.

The following list of topics represent potential areas for patient education. All of the topics may not be relevant for all women.

Practice issues Number and frequency of prenatal visits Routine pregnancy monitoring (eg, maternal weight, blood pressure, uterine growth, fetal activity and heart rate, possible ultrasound examination) How to reach the provider after business hours, coverage arrangements, and the role of office personnel (eg, nurses, midwives) Confidentiality issues (eg, information left on phone answering machines, use of electronic mail, and discussions with family members). There should be an explanation of the Health Insurance Portability and Accountability Act of 1996 (HIPAA) and how it affects the patient (information is available at www.hhs.gov/ocr/hipaa/).

Seat belts — Pregnant women should continue wearing three-point seat belts during pregnancy. The lap belt is placed across the hips and below the uterus; the shoulder belt goes between the breasts and lateral to the uterus. Although there are case reports of maternal and fetal injuries resulting from seat belt use, the overall effect is that seat belts appear to protect mother and fetus [32] .

Vitamins, nutrition, and weight gain — A standard prenatal multivitamin with iron satisfies the daily requirements of most pregnant women. Well-nourished women may not need multivitamins to satisfy these daily requirements, but in the absence of a careful evaluation by a nutritionist, it is prudent to recommend them. Folate supplements to prevent neural tube defects are recommended prior to conception and throughout the first trimester.

Use of vitamins and minerals, nutrition and weight gain, as well as antigen avoidance diets and foods/supplements that should be limited or avoided (eg, fish, caffeine, excess intake of vitamin A), are discussed in detail separately. (See "Nutrition in pregnancy" and see "Prevention of neural tube defects").

Substance use — Maternal alcohol consumption, smoking, or use of illicit drugs can be harmful to the fetus. Patients who have problems with substance use should be strongly advised of the risks of this behavior and referred to cessation programs in their area. (See "Smoking and pregnancy", see "Alcohol intake and pregnancy", and see "Substance use in pregnancy")

Infection precautions — Some infections are potentially harmful in pregnancy and interventions exist to minimize the risk of these infections. In general, pregnant women should avoid contact with people with febrile illnesses that could be contagious. Influenza — Influenza vaccination is recommended for women who will be pregnant during the influenza season, regardless of stage of pregnancy. (See "Immunization of pregnant women"). Toxoplasmosis (See "Toxoplasmosis and pregnancy") Cytomegalovirus (See "Cytomegalovirus infection in pregnancy") Listeria (See "Epidemiology and pathogenesis of Listeria monocytogenes infection") Varicella (See "Varicella-zoster virus infection in pregnancy") Parvovirus (See "Parvovirus B19 infection during pregnancy" and see "Treatment and prevention of parvovirus B19 infection") Infections associated with pets — Women who are pregnant or planning pregnancy should avoid contact with all rodents [33] . Precautions about handling pets and laboratory animals are discussed in topic reviews on each animal (see topic reviews on zoonotic infection). Foodborne infections (See "Nutrition in pregnancy" section on Avoidance of foodborne illnesses).

Work — A woman with an uncomplicated pregnancy who is employed where there are no greater potential hazards than those encountered in routine daily life may continue to work without interruption until the onset of labor. However, the physical demands of the woman's job should be considered, especially in women at higher risk of preterm delivery. (See "Work and pregnancy").

Exercise — Healthy women with uncomplicated pregnancies should continue to exercise during pregnancy. Issues regarding type, frequency, and duration of exercise, as well as risks of and contraindications to exercise, are reviewed separately. (See "Recommendations for exercise during pregnancy and the postpartum period" and see "Anatomical and physiological changes of pregnancy and exercise").

Sexual activity — Theoretically, sexual intercourse may stimulate labor due to physical stimulation of the lower uterine segment, endogenous release of oxytocin as a result of orgasm, direct action of prostaglandins in semen, or increased exposure to infectious agents. However, in the absence of pregnancy complications (eg, vaginal bleeding, ruptured membranes), there is insufficient evidence to recommend against sexual intercourse during pregnancy. Most studies have not shown an increased risk of preterm labor/delivery or infectious complications (unless a sexually transmitted disease is acquired) [37,38] .

Birth defects and genetic issues — The prevalence of birth defects of medical, surgical, or cosmetic significance is 2 to 4 percent among live born infants and does not vary

among ethnic groups. Both genetic and environmental factors play a role in their pathogenesis. (See "Etiology of birth defects").

The clinician should discuss the causes of congenital anomalies with the patient, assess the specific risk for her child, review options for and limitations of prenatal diagnosis, and decide whether additional testing and referral to a geneticist would be useful.

Use of medications — Medication use is common in pregnancy [39] . All patients should be encouraged to contact their provider with any concerns and before taking any drugs (prescription, over the counter, or herbal [alternative] remedies) that were not previously approved.

Since 1975, the US Food and Drug Administration (FDA) has assigned pregnancy risk factors to all drugs available in the United States (show table 7). Information on the use of specific drugs in pregnancy, including the FDA risk category and pregnancy implications, is available in the UpToDate drug database, as well as in topics that review treatment of medical conditions in pregnant women.

Acetaminophen is a widely used drug for treatment of pain and fever, with no evidence in humans of increased risk of pregnancy loss, congenital anomalies, or neurodevelopmental delay [40] . The extensive use of acetaminophen by pregnant women combined with the paucity of documented adverse effects have served to make this medication the pain reliever and antipyretic of choice during pregnancy when drug therapy is indicated [41] . The risks and benefits of using nonsteroidal antiinflammatory drugs for treatment of pain or fever depend on the dose, gestational age, and duration of therapy. (See "Inhibition of acute preterm labor" section on Cylooxygenase inhibitors).

Over-the-counter and prescription drugs for treatment of respiratory infections and allergies are discussed in detail separately. (See "Treatment of respiratory infections in pregnant women" and see "Recognition and management of allergic disease during pregnancy").

Constipation and diarrhea can be managed with bulk-forming preparations containing fiber (eg, Metamucil) and kaolin and pectin (Kaopectate), respectively. (See "Maternal gastrointestinal tract adaptation to pregnancy").

Nausea and vomiting may be pregnancy-related, or due to other causes. Supportive care is similar regardless of the etiology. (See "Clinical features and diagnostic evaluation of nausea and vomiting of pregnancy (hyperemesis gravidarum and morning sickness)").

Airline travel — Most airlines allow women to fly up to 35 to 36 weeks of gestation, although individual policies may vary. Commercial airline travel is generally safe for women with uncomplicated pregnancies [42-45] . Fetal heart rate is not affected during flight if the mother and fetus are healthy [43] . Although some studies have shown a trend toward increased risk of spontaneous abortion in flight attendants [42,46] and increased

preterm birth among women who fly long durations and frequently [47] , this could be due to not accounting for relevant differences between the study subjects and controls.

Maternal physiologic adaptations to high altitude include hemoconcentration, increased heart rate and blood pressure, and decreased aerobic capacity with reduction of partial oxygen pressure [43,48] . For these reasons and the lack of availability of emergency care, certain precautions should be taken: Women with complicated pregnancies that may be exacerated by flight conditions or require emergency care should avoid air travel [44] . All airline travelers should maintain hydration, periodically move their lower extremities to avoid stasis and potential venous thrombosis, and continuously wear seat belts to protect against unexpected turbulence. Use of support stockings and avoidance of restrictive clothing may be helpful [44] . Supplemental oxygen should be administered to pregnant women who must travel and may not tolerate the hypoxic environment of high altitude flying, even in pressurized aircraft (eg, women with sickle cell or cyanotic heart disease) [44] . (See "Traveling with oxygen aboard commercial air carriers").

The amount of cosmic radiation received during airline travel is below the level at which there begins to be concern about possible harmful fetal effects (20 millisievert or 2 rem) [49] . As an example, a woman on a round trip transpolar flight from New York to Tokyo would be exposed to approximately 15 mrem cosmic radiation; for a round trip transcontinental flight across the United States, the exposure would be 6 mrem. By comparison, the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection (NCRP) recommended limit for maximum cumulative radiation exposure for a member of the general public over one year is 100 mrem [50,51] . Pilots, flight attendants, and frequent fliers might exceed this level. They should be aware of their personal radiation exposure, which can be calculated using the Federal Aviation Administration Radiobiological Team web site (jag.cami.jccbi.gov./cariprofile.asp). A detailed discussion of radiation risks in pregnancy can be found separately. (See "Diagnostic imaging procedures during pregnancy").

Travel to moderate and high altitudes — Airplane passenger cabins are usually pressurized to an altitude of 5000 to 8000 feet (1524 to 2438 meters). The PO2 values at these altitudes are 132 and 118 mmHg, respectively (show table 8) [48] . Pregnant women may be exposed to altitudes in this range from other sources, such as visiting a mountain resort or traveling in a hot air balloon or noncommercial aircraft. There is scant literature about acute, short-term exposure of pregnant women to these moderate altitudes. One study evaluated seven women in the third trimester at sea level (180 feet) and then within two to four days of visiting a facility at 6000 feet (1829 m) [48] . Plasma glucose rose from 4.53 to 5.51 mmol/L (81.6 to 99.2 mg/dL); however, maternal heart rate, oxygen consumption, ventilation, tidal volume, and plasma catecholamine and lactate levels did not change significantly, nor was there a change in fetal heart rate.

These data and other reports [52,53] , although limited, are reassuring that women with uncomplicated pregnancies can tolerate acute exposure to moderate altitudes. Since an individual's altitude tolerance cannot be reliably determined at sea level, advice on travel to intermediate altitudes should err on the side of caution [52,53] .

High altitudes (over 8000 feet/2438 m) are more likely to cause problems. In general, exposure of a pregnant woman to the hypoxia of high altitude results in acclimatization responses, which preserve the fetal oxygen supply. The fetus also can utilize some compensatory mechanisms during brief periods of hypoxia. However, these adaptive mechanisms may not be fully compensatory in complicated pregnancies, such as those with uteroplacental insufficiency, or at very high altitudes [54] . As an example, pregnancy in inhabitants of Cerro de Pasco, Peru (altitude 4370 m) is associated with 31 percent lower maternal cardiac output and 11 percent lower birthweight than observed in pregnant women residing at sea level (mean birth weight 2935 and 3290 grams, respectively) [55] .

A survey of obstetrical care providers in Colorado reported that preterm labor and bleeding complications of pregnancy were the most commonly encountered pregnancy complications among pregnant visitors to high altitudes [56] . Dehydration, engaging in strenuous exercise before acclimatization, and participation in activities with high risk of trauma were behaviors that could increase the risk of pregnancy complications. An altitude of 8000 feet should not be exceeded in the first few days of short-term exposure to high altitude [52] . (See "High altitude illness: Physiology, risk factors, and general prevention").

FOLLOW-UP VISITS — Two major goals of prenatal care in the last half of pregnancy are diagnosis of preeclampsia and fetal malpresentation.

Routine examination at each prenatal visit typically consists of measurement of blood pressure and weight, measurement of the uterine fundus to assess fetal growth, auscultation of fetal heart tones, assessment of fetal activity (in the second and third trimesters), and determination of fetal presentation (in the third trimester). These simple, noninvasive, inexpensive procedures detect 50 percent of fetuses with growth abnormality, prevent 70 percent of eclampsia, and uncover 80 percent of breech presentations prior to labor [57-59] .

Urine is generally screened for protein and glucose at each visit, although the value of these tests is questionable in women with normal blood pressure and who have been screened for gestational diabetes [60-63] .

There is evidence from epidemiologic studies that improved detection and care of women with hypertensive disorders of pregnancy improves outcome [62] . In addition, randomized trials have shown that external cephalic version of the breech fetus is an effective procedure for increasing the chance of cephalic presentation at onset of labor and decreasing the rate of cesarean delivery (assuming vaginal breech delivery is not desired). In contrast, clinical or sonographic suspicion of fetal growth restriction has not been proven to improve perinatal outcome. (See "Clinical features; diagnosis; and long-term prognosis of preeclampsia" and see "External cephalic version" and see "Sonography" below).

Frequency of prenatal visits — There are limited data as to what constitutes the optimal number and frequency of prenatal visits. In the United States, the minimum intervals for prenatal visits suggested for women with uncomplicated pregnancies are every four to five weeks until 28 weeks of gestation, every two to three weeks from 28 to 36 weeks, and then weekly until delivery [64] . According to this schedule, a woman whose first visit is at 6 weeks of gestation and whose last visit is at 41 weeks will have 16 prenatal visits.

This regimen has been questioned given the cost and time constraints of modern society and lack of proven efficacy in randomized trials [3,62,65-70] . One study randomly allocated 2764 low risk women to traditional prenatal care (14 visits) or reduced care (nine visits) [67] . There was no difference in any maternal or fetal outcome between groups. Another series, which included over 24,000 women, compared pregnancy outcome of women primarily assessed as high-risk at the first prenatal visit and who received standard obstetrical care to women assessed as low risk who received a new model of care (fewer clinic visits but with emphasis on interventions known to be effective for improving maternal or neonatal outcomes) [68] . The median number of prenatal visits in the standard and new model groups was eight and five, respectively, with no difference in adverse pregnancy outcomes.

More frequent visits may be of benefit in monitoring women with diabetes, hypertension, threatened preterm birth, postterm pregnancies, and other pregnancy complications. There is no evidence that frequent visits improve pregnancy outcome in low risk pregnancies. However, women have expressed a personal preference for more, rather than fewer, visits [3] .

Second and third trimester laboratory tests

Screening for neural tube defects and Down syndrome — All pregnant women should be offered screening for neural tube defects and Down syndrome (if not already performed in the first trimester). (See "Prenatal screening and diagnosis of neural tube defects" and see "Second trimester maternal serum screening for Down syndrome").

Gestational diabetes — Universal screening for gestational diabetes is recommended at 24 to 28 weeks of gestation. (See "Screening and diagnosis of gestational diabetes mellitus"). Screening should also be considered in the first trimester in women with significant risk factors (ie, obesity, prior history of gestational diabetes, prior macrosomic infant).

Sexually transmitted disease — Testing for sexually transmitted diseases (eg, HIV [71] , syphilis, hepatitis B surface antigen, chlamydia, gonorrhea) should be repeated in the third trimester in women who are at continued risk and for those who acquired a new risk factor during pregnancy (eg, a new or more than one sex partner, evaluation or treatment for a STD, injection of nonprescription drugs); all women under age 25 years should be retested for Chlamydia trachomatis late in pregnancy [72] . In some areas, repeat testing for syphilis and HIV is mandatory.

Blood count and antibody screening — A hemoglobin or hematocrit should be repeated early in the third trimester to assess for anemia. Increased iron and folate requirements of pregnancy may result in anemia, which can be corrected by appropriate supplementation. Prevention of anemia may decrease the need for blood transfusion, and associated risks, if hemorrhage occurs.

Antibody screening is repeated in unsensitized Rh(D)-negative women and anti(D)-immune globulin administered, as indicated. Although there is good evidence that administration of anti(D)-immune globulin is cost effective, there are no data that establish the cost-effectiveness of repeat antibody screening at this time if the initial antibody screen was negative. (See "Prevention of Rh(D) alloimmunization").

Group B beta-hemolytic streptococcus testing — All pregnant women should be screened for group B beta-hemolytic streptococcus (GBS) colonization with swabs of both the lower vagina and rectum at 35 to 37 weeks of gestation. The only patients who are excluded from screening are those with GBS bacteriuria earlier in the current pregnancy or those who gave birth to a previous infant with invasive GBS disease. These latter patients are not included in the screening recommendation because they should receive intrapartum antibiotic prophylaxis regardless of the colonization status. Intrapartum chemoprophylaxis of colonized women has been proven to reduce the incidence of early-onset neonatal GBS. (See "Chemoprophylaxis for the prevention of neonatal group B streptococcal disease").

Sonography — Although early identification of growth-restricted fetuses allows for closer surveillance and earlier intervention in case of decompensation, the use of ultrasound in the third trimester to screen for fetal growth disturbance in low risk women has not been effective for reliably detecting these fetuses or improving outcome. (See "Routine prenatal ultrasonography as a screening tool").

Fetal assessment — Sonographic and cardiographic fetal assessments are indicated in patients at-risk for fetal complications. (See "Ultrasound examination in obstetrics and gynecology" and see "Antepartum fetal heart rate assessment" and see "The fetal biophysical profile").

Signs and symptoms to be reported to the health care provider — These include: Vaginal bleeding (See "Overview of the etiology and evaluation of vaginal bleeding in pregnant women") Leakage of fluid per vagina (See "Preterm premature rupture of membranes") Uterine contractions (See "Overview of preterm labor and delivery") Decreased fetal activity (See "Antepartum fetal heart rate assessment") Signs of preterm labor (eg, low, dull backache; increased uterine activity compared to previous patterns; menstrual-like cramps; diarrhea; increased pelvic pressure; vaginal leaking of clear fluid, spotting, or bleeding) (See "Prevention of spontaneous preterm birth")

In addition, signs or symptoms suggestive of a medical or surgical disorder should be reported.

Second and third trimester counseling — A number of issues may be discussed in preparation for labor and delivery. These include, but are not limited to: Route of delivery — (See "Cesarean delivery on maternal request" and see "Trial of labor after cesarean delivery") Management of labor — (See "Pharmacologic management of pain during labor and delivery" and see "Preparation for labor and childbirth") Postpartum issues — (See "Overview of postpartum care") Breast feeding — (See "Breastfeeding: Parental education and support", sectio on Prenatal). Neonatal circumcision — (See "Circumcision: Risks and benefits")

INFORMATION FOR PATIENTS — Educational materials on this topic are available for patients. (See "Patient information: Avoiding infections in pregnancy" and see "Patient information: First trimester and integrated screening for Down syndrome" and see "Patient information: Second trimester screening for Down syndrome" see "Patient information: Group B streptococcus and pregnancy"). We encourage you to print or e-mail these topic reviews, or to refer patients to our public web site, www.uptodate.com/patients, which includes these and other topics.

SUMMARY AND RECOMMENDATIONS Studies have not established that prenatal care improves birth outcomes definitively, and it is not clear which components of prenatal care are most effective. However, all of these studies are flawed by multiple confounders. (See "Introduction" above and see "Frequency of prenatal visits" above and see "Care provider" above). In low risk pregnancies, there is good evidence that decreasing the number of prenatal visits to as few as four or five and using midwives to provide prenatal care is cost-effective and does not adversely affect outcome. (See "Introduction" above and see "Frequency of prenatal visits" above). There is insufficient evidence on which to base recommendations on the optimal content of prenatal care. However, there is good evidence for the following (See "Laboratory tests" above):

      - We recommend screening for asymptomatic bacteriuria (Grade 1A). Untreated asymptomatic bacteriuria in pregnant women often results in pyelonephritis, and detection and treatment prevent upper tract infection and its sequelae.

      - We recommend screening all pregnant women for group B beta-hemolytic streptococcus (Grade 1A). Peripartum detection and treatment of group B beta-hemolytic streptococcus minimizes the risk of vertical transmission. We recommend screening at-risk women for sexually transmitted infections (Grade 1B). Treatment is indicated to prevent horizontal and vertical transmission, as well as maternal sequelae.

      - We recommend offering screening for selected fetal structural and chromosomal abnormalities (Grade 1B). Prenatal diagnosis can detect many fetal structural and chromosomal abnormalities. Determining women at risk of having offspring with these abnormalities allows them additional options for evaluation and management of these conditions.

      - We recommend administration of anti(D)-immune globulin to women at risk of alloimmunization (Grade 1A). Prophylactic anti(D)-immune globulin administration reduces the risk of hemolytic disease of the newborn.

      - We recommend screening for preeclampsia (Grade 1B) and fetal malpresentation (Grade 1A). Recognition of preeclampsia and appropriate intervention improve outcome; recognition of fetal malpresentation combined with external cephalic version results in fewer cesarean deliveries in areas where vaginal breech delivery is practiced. (See "Follow-up visits" above).