DOPPLER ULTRASOUND in Pregnancy

Doppler Ultrasound in the Management of Fetal Growth Restriction

Chukwuma I. Onyeije, M.D.

Atlanta Perinatal Associates

For your convenience a copy of this lecture is available for review and download at http://onyeije.net/present

Terminology

Intrauterine Growth Restriction - IUGRSmall for Gestational Age - SGAFetal growth restriction - FGR

Because classification of LBW as due to preterm birth or IUGR requires valid estimates of gestational age (GA), attention is required to improving the availability and quality of GA estimates on a population-wide basis in developing countries. This includes, where feasible, recording early in pregnancy the mother's recall of the date her last normal menstrual period began and the training of birth attendants (traditional birth attendants, midwives, nurses, and physicians) in the physical assessment of the newborn (Dubowitz, Ballard, or Capurro scores). In developed countries, early (< 20 weeks) ultrasound examination has improved the validity and reliability of GA assessment, although evidence from randomized trials does not demonstrate improvement in maternal or fetal/infant outcomes with routine early ultrasound.An international fetal growth reference curve should be developed based on pooled data from countries in different geographic regions where fetal growth is believed optimal. Care should be taken to ensure that such a reference fits with the new infant growth reference currently being developed under WHO auspices. Further research is needed to identify those determinants of fetal growth that influence mortality, morbidity, and performance independently of their effects on growth. Although it is quite clear that the use of sex-specific reference curves is justifiable, additional research is needed using large populations and ultrasound confirmation of GA to assess whether infants of different races born at a particular weight for gestational age are at substantially different risks for important health outcomes. Similar research is needed to determine whether infants who are born small because their mothers are primiparous or of short stature or living at high altitude are at the same risk for adverse sequelae as those of equivalent size who are small because, for example, their mothers have pre-eclampsia or smoke cigarettes. Until this information is available, the use of a single, sex-specific international reference has much to recommend it.

Definitions

Intrauterine growth retardation (IUGR)

Fetus is at or below the 10th percentile for EGA

Fetus is subjected to pathology that restricts its ability to grow.

Small for Gestational Age:

A small but otherwise healthy fetus.

Low Birth weight (LBW)

Birth weight of less than 2500 gms which could be due to IUGR or prematurity

Description
There are standards or averages in weight for unborn babies according to their age in weeks. When the baby's weight is at or below the 10th percentile for his or her age, it is called intrauterine growth retardation or fetal growth restriction. These babies are smaller than they should be for their age. How much a baby weighs at birth depends not only on how many weeks old it is, but the rate at which it has grown. This growth process is complex and delicate. There are three phases associated with the development of the baby. During the first phase, cells multiply in the baby's organs. This occurs from the beginning of development through the early part of the fourth month. During the second phase, cells continue to multiply and the organs grow. In the third phase (after 32 weeks of development), growth occurs quickly and the baby may gain as much as 7 ounces per week. If the delicate process of development and weight gain is disturbed or interrupted, the baby can suffer from restricted growth.

Traditional Classification of IUGR

Symmetrical

Asymmetrical

Fetal brain is abnormally large when compared to the bodyOccurs when the fetus experiences a problem during later development

Fetal head and body are proportionately small. Occurs with early developmental problems.

Application of the international foetal growth reference curve will vary according to its specific clinical and public health uses or purposes. Criteria for diagnosis of foetal growth restriction (e.g., SGA) should be related to evidence of increased risk for perinatal mortality and/or other indices of adverse outcomes. The new reference should provide percentiles [(e.g., 3rd, 5th, 10th, 15th, 25th, 50th (median), 75th, 85th, 90th, 95th, and 97th)] as well as z-scores [(e.g., -3, -2, -1, 0 (mean), 1, 2, and 3 SD)], so that health planners and practitioners can use the most appropriate cut off based on local circumstances.Proportionality at birth may be related to adverse outcomes. Thus there is a need to develop reference data for birth length and head circumference in relation to GA, and for birth weight in relation to birth length. Because the concepts of 'wasting' and 'stunting' have proven useful for categorizing undernourished infants and older children, an attempt should be made to quantify the mortality and morbidity risks associated with 'wasted' and 'stunted' newborns and to develop indicators for their classification.

In a normal infant, the brain weighs about three times more than the liver. In asymmetrical IUGR, the brain can weigh five or six times more than the liver.

Normal Small Fetus

Abnormal Small Fetus

Growth Restricted Fetus

Functional Classification

Normal Small Fetus:

No Structural abnormality. Normal umbilical Doppler. Normal AFI.

Less than 10th percentile.

Good prognosis. No increased risk. No special care provided.

.

Functional Classification

Abnormal Small Fetus:

Chromosomal abnormality or structural defect with small size.

Poor prognosis.

Functional Classification

Growth Restricted Fetus:

Small due to placental dysfunction

Variable prognosis.

Appropriate and timely treatment can improve outcome.

Functional Classification

Maternal Risk Factors

Multiple gestation

Drug exposure

Cardiovascular disease

Kidney disease

Chronic infections

UTI, Malaria, TB, genital infections

Autoimmune disease

Most of the evidence on etiologic determinants is based on observational studies and systematic overviews or meta-analyses of such studies. In developing countries, the major determinants of IUGR are nutritional: low gestational weight gain (primarily due to inadequate energy intake), low pre-pregnancy BMI (reflecting chronic maternal undernutrition), and short maternal stature (principally due to undernutrition and infection during childhood). Gastroenteritis, intestinal parasitosis, and respiratory infections are prevalent in developing countries and may also have an important impact. Malaria is a major determinant in countries where that disease is endemic. Cigarette smoking is an increasingly important factor in some settings.In developed countries, cigarette smoking is far and away the most important etiologic determinant, but low gestational weight gain and low pre-pregnancy BMI are also determinants. The etiologic roles of pre-eclampsia, short stature, genetic factors, and alcohol and drug use during pregnancy are well-established but quantitatively less important. Socioeconomic disparities in IUGR risk within developed countries are largely attributable to socioeconomic gradients in smoking, weight gain and maternal stature. In poor urban areas where cocaine abuse is highly prevalent, this may also be important.

Fetal Risk Factors

TORCH infections

Fetal anomalies

Aneuploidy

Skeletal Dysplasia

Hypoxia

The etiologic role of micronutrients in IUGR remains to be clarified. The best evidence concerning their importance derives from randomized trials and from systematic overviews of those trials contained in the Cochrane Collaboration Pregnancy and Childbirth database. Unfortunately, there are few supplementation or fortification trials in developing country settings where deficiencies in these micronutrients are prevalent. Trials are required to define the possible etiologic roles of iron, calcium, vitamin D, and vitamin A, especially in developing countries. The evidence concerning folate, magnesium, and zinc also looks sufficiently promising to justify further investigation.The physiologic and molecular mechanisms by which nutritional or other determinants affect fetal growth are incompletely understood. Growth is determined not only by substrate availability but also by the integrity of physiologic processes necessary to ensure transfer of nutrients and oxygen to the developing fetus. Expansion of maternal plasma volume, maintenance of uterine blood flow, and development of adequate placentation are key physiologic mechanisms required for optimal fetal growth. All substances used by the fetus are transported by the placenta: some (like oxygen and most other gases) by passive diffusion, others by facilitated transport proteins (e.g., Glut 1 for glucose), and still others (e.g., amino acids) by active energy-dependent transport processes. Insulin-like growth factors (IGFs) are important mediators of substrate incorporation into fetal tissue. IGF1 appears to induce cell differentiation, including (perhaps) oligodendrocyte development in the brain, whereas IGF2 may function to stimulate mitosis. It remains uncertain whether these physiologic and molecular mechanisms are merely the final common pathways for genetic or environmental determinants of IUGR, or whether they themselves vary (favorably or pathologically) independently of those determinants.

Placental Factors

Uteroplacental insufficiency

Improper placentation in the first trimester.

Abnormal insertion of placenta.

Reduced maternal blood flow to the placenta.

Fetoplacetal insufficiency due to-.

Vascular anomalies of placenta and cord.

Decreased placental functioning mass-.

Small placenta, abruptio placenta, placenta previa, postdates

The etiologic role of micronutrients in IUGR remains to be clarified. The best evidence concerning their importance derives from randomized trials and from systematic overviews of those trials contained in the Cochrane Collaboration Pregnancy and Childbirth database. Unfortunately, there are few supplementation or fortification trials in developing country settings where deficiencies in these micronutrients are prevalent. Trials are required to define the possible etiologic roles of iron, calcium, vitamin D, and vitamin A, especially in developing countries. The evidence concerning folate, magnesium, and zinc also looks sufficiently promising to justify further investigation.The physiologic and molecular mechanisms by which nutritional or other determinants affect fetal growth are incompletely understood. Growth is determined not only by substrate availability but also by the integrity of physiologic processes necessary to ensure transfer of nutrients and oxygen to the developing fetus. Expansion of maternal plasma volume, maintenance of uterine blood flow, and development of adequate placentation are key physiologic mechanisms required for optimal fetal growth. All substances used by the fetus are transported by the placenta: some (like oxygen and most other gases) by passive diffusion, others by facilitated transport proteins (e.g., Glut 1 for glucose), and still others (e.g., amino acids) by active energy-dependent transport processes. Insulin-like growth factors (IGFs) are important mediators of substrate incorporation into fetal tissue. IGF1 appears to induce cell differentiation, including (perhaps) oligodendrocyte development in the brain, whereas IGF2 may function to stimulate mitosis. It remains uncertain whether these physiologic and molecular mechanisms are merely the final common pathways for genetic or environmental determinants of IUGR, or whether they themselves vary (favorably or pathologically) independently of those determinants.

Diagnosis of IUGR

Difficult diagnosis

Need to evaluate risk factors

Serial ultrasounds important

Dating is important

Ultrasound signs

Inadequate fetal interval growth.

Reduced AFI.

Placental calcification.

IUGR can be difficult to diagnose and in many cases doctors are not able to make an exact diagnosis until the baby is born. A mother who has had a growth restricted baby is at risk of having another during a later pregnancy. Such mothers are closely monitored during pregnancy. The length in weeks of the pregnancy must be carefully determined so that the doctor will know if development and weight gain are appropriate. Checking the mother's weight and abdomen measurements can help diagnose cases when there are no other risk factors present. Measuring the girth of the abdomen is often used as a tool for diagnosing IUGR. During pregnancy, the healthcare provider will use a tape measure to record the height of the upper portion of the uterus (the uterine fundal height). As the pregnancy continues and the baby grows, the uterus stretches upward in the direction of the mother's head. Between 18 and 30 weeks of gestation, the uterine fundal height (in cm.) equals the weeks of gestation. If the uterine fundal height is more than 2-3 cm below normal, then IUGR is suspected. Ultrasound is used to evaluate the growth of the baby. Usually, IUGR is diagnosed after week 32 of pregnancy. This is during the phase of rapid growth when the baby should be gaining more weight. IUGR caused by genetic factors or infection may sometimes be detected earlier.

The Growth Restricted Neonate

Normal & IUGR Newborn babies

Normal & IUGR Placentas

The Growth Restricted Placenta

Surveillance

Duration: Until delivery occurs

Reason: To identify further progression of the disease process that would jeopardize the fetus.

Modalities: NST, AFI, Doppler, BPP

Systematic reviews provide strong evidence of benefit only for the following interventions: balanced protein/energy supplementation, strategies to reduce maternal smoking, and antimalarial prophylaxis. In Jamaica, antibiotic administration to prevent urinary tract infections further reduced an already low prevalence of IUGR. Improvement of maternal nutrition should be a priority, especially in developing countries. Unless maternal undernutrition is severe, the effect of balanced protein/energy supplementation on birth weight is likely to be modest 100 g). Reduction in maternal smoking should be encouraged, both by individual clinicians (using behavioral modification techniques, for example) and by policy makers (e.g., taxes on cigarettes and other tobacco products). Antimalarial chemoprophylaxis should be provided in endemic areas, particularly to primigravidae, although more research is needed to elucidate the ideal timing of treatment, combination of agents, and safety for the fetus.

Doppler ultrasonography was first used to study flow velocity in the fetal umbilical artery in 1977

Doppler In IUGR

DOPPLER WORKS LIKE AN ECHO

T1 : time of omitted signal .T2 : time of returned signal .

T2 T1 = time difference or phase shift .

The Doppler frequency is obtained from phase shift.

AS TIME DIFFERENCE DECREASE THE DOPPLER FREQUENCY INCREASE.

pulse repetition frequency

(T2 T1) phase shift with known beam / flow angle can calculate flow velocity .

T1

T2

Basic Principals

The time difference or phase shift can be processed to produce either colorflow display or aDoppler sonogram

Basic Principles

The angle q between the beam and the direction of flow is VERY important in the use of Doppler ultrasound.

Freq.

q

The angle of insonation

Flow velocity

3

2

1

Factors affecting doppler frequency

Beam (A) is more aligned than (B)

The beam/flow angle at (C) is almost 90 and there is a very poor Doppler signal

The flow at (D) is away from the beam and there is a negative signal.

Why the Different Waveforms?

Aliasing

If a second pulse is sent before the first is received, the receiver cannot discriminate between the reflected signal from both pulses and aliasing occur.

So to eliminate aliasing The pulse repetition frequency or scale is set appropriately for the flow velocities

Aliasing

Umbilical artery Doppler

Doppler indices

UMBILICAL ARTERY FLOW Arterial flow has a saw-tooth pattern of arterial flow in one direction Venous blood flow is continuous in the other direction.

Umbilical artery

FACTORS AFFECTING UMBILICAL ARTERY DOPPLER FLOW VELOCITY WAVEFORMS*

Doppler of the Umbilical Artery

An increasing trend in Doppler suggests deteriorating condition.

This is an example of a foetus at risk for IUGR in which the amniotic fluid index was measured but the nurses and physician did not understand the principles of an abnormal reading. The foetus was allowed to remain in utero and developed cerebral palsy from oxygen deprivation. The family sued the hospital and the physician and was awarded 9.7 million dollars which was the largest malpractice award in the state of Utah

This is the amniotic fluid index in the above case. The blue represents the normal range. At 35 weeks the fluid measurement was 16. Four days later it dropped to 6.3. This sudden drop was ignored by the nurses and physician caring for the patient. A few days later the fetus was damaged because the umbilical cord was compressed, resulting in cerebral palsy.

Middle cerebral artery doppler

The middle cerebral artery can be seen as a major lateral branch of the circle of WillisIt runs anterolaterally at the borderline between the anterior and the middle cerebral fossae

Middle cerebral artery

Redistribution of blood flow occurs as an early stage in fetal adaptation to hypoxemia ( brain-sparing reflex) Increased blood flow to protect the brain, heart, and adrenals Reduced flow to the peripheral and placental circulations

Middle cerebral artery

MCA Doppler wave form of early stage of fetal hypoxemia

increased end-diastolic flow in the middle cerebral artery (lower MCA pulsatility index or resistance index)

Average of both MCAs must be calculated for more precise result

Middle Cerebral Artery

Flow velocity waveform in the fetal middle cerebral artery in a severely anemic fetus at 22 weeks (left) and in a normal fetus (right). In fetal anemia, blood velocity is increased

When the fetus is hypoxic, the cerebra arteries tend to become dilated in order to preserve the blood flow to the brain and The systolic to diastolic ratio will decrease (due to an increase in diastolic flow)

Middle Cerebral Artery

MCA Doppler Calculations

The brain sparing effect is manifested by :A DECREASED PULSATILITY INDEX (PI):THE PULSATILITY INDEX = ([peak systolic velocity minus lowest diastolic velocity] divided by [mean velocity]) -or-S-D / AMCA DOPPLER CALCULATOR:

Doppler ultrasound for the fetal assessment in high-risk pregnancies

A reduction in perinatal deaths.

Fewer inductions of labour .

Fewer admissions to hospital .

no report of adverse effects .

No difference was found for fetal distress in labour .

No difference in caesarean delivery .

The 4 Ts Recalled

THROMBIN

Check labs if suspicious.

Short Term Risks of IUGR

Increased perinatal morbidity and mortality.

Intra uterine / Intrapartum death.

Intrapartuum foetal acidosis characterized by-.

Late deceleration.

Severe variable deceleration.

Beat to beat variability.

Episodes of bradicardia.

Intrapartum foetal acidosis may occur in as many as 40 % of IUGR, leading to a high incidence of LSCS.

IUGR infants are at greater risk of dying because of neonatal complications- asphyxia, acidosis, meconium aspiration syndrome, infection, hypoglycemia, hypothermia, sudden infant death syndrome.

IUGR infants are likely to be susceptible to infections because of impaired immunity

Long term Prognosis

Babies who suffer from IUGR are at an increased risk for death, low blood sugar, low body temperature, and abnormal development of the nervous system. These risks increase with the severity of the growth restriction.

The growth that occurs after birth cannot be predicted with certainty based on the size of the baby when it is born.

Infants with asymmetrical IUGR are more likely to catch up in growth after birth than are infants who suffer from prolonged symmetrical IUGR.

If IUGR is related to a disease or a genetic defect, the future of the infant is related to the severity and the nature of that disorder.

Long term Prognosis

IUGR infants are more likely to remain small than those of normal birth weight. They will need the special attention of primary health, nutrition and social services during infancy and early childhood.

Implication of IUGR can be life long affecting:

Body size growth, composition and physical performance.

Immunocompetence.

It appears to predispose to adult adult-onset, degenerative diseases like maturity onset diabetes and cardiovascular diseases.

Each case is unique. Can not reliably predict an infant's future progress.

Babies who suffer from IUGR are at an increased risk fordeath, low blood sugar, low body temperature, and abnormal development of the nervous system. These risks increase with the severity of the growth restriction. The growth that occurs after birth cannot be predicted with certainty based on the size of the baby when it is born. Infants with asymmetrical IUGR are more likely to catch up in growth after birth than are infants who suffer from prolonged symmetrical IUGR. However, as of 1998, doctors cannot reliably predict an infant's future progress. Each case is unique. Some infants who have IUGR will develop normally, while others will have complications of the nervous system or intellectual problems like learning disorders. If IUGR is related to a disease or a genetic defect, the future of the infant is related to the severity and the nature of that disorder.