Chapter 37 Postterm Pregnancy

OBGY R1 Lee Eun Suk

Williams Obstetrics

Postterm Pregnancy

The term postterm, prolonged, postdates, and postmature are often loosely used interchangeably to signify pregnancies that have exceeded a duration considered to be the upper limit of normal

Postmature should be used to described the infant with recognizable clinical features indicating a pathologically prolonged pregnancy

Postdates probably should be abandoned, because the real issue in many postterm pregnancies is “post-what dates?”

Therefore, postterm or prolonged pregnancy is preferred expression for an extended pregnancy

The standard of definition of prolonged pregnancy → 42 completed weeks (294days) or more from the first day of the last menstrual period

Postterm Pregnancy

Estimated Gestational Age Using Menstrual Dates

Two categories of pregnancies that reach 42 complete weeks

Those truly 40 weeks past conception Those of less advanced gestation due to inaccurate estimate of gestational age

Blondel and colleagues (2002)

Analyzed postterm pregnancy rates based on either the last menstrual period, ultrasound at 16 to 18 weeks, or both The proportion of births at 42 weeks or longer was 6.4 % when based on th

e last menstrual period alone & 1.9 % when based on USG alone This raises the possibility that the menstrual dates are frequently inaccurate in predicting postterm pregnancy

Postterm Pregnancy

Estimated Gestational Age Using Menstrual Dates

Most pregnancies that are reliably 42 completed weeks beyond the last menses probably are not biologically prolonged

Conversely, a few that are not yet 42 weeks might be postterm

Because there is no method to identify pregnancies that are trulyprolonged, all pregnancies judged to be 42 completed weeks should be managed as if abnormally prolonged

Postterm Pregnancy

Incidence

Maternal demographic factors

Parity, prior postterm birth, socioeconomic class, and age

The incidence of a subsequent postterm birth

Increased from 10 to 27% if the first birth was postterm

↑ 39% if there had been two previous postterm deliveries

When mother and daughter had had a prolonged pregnancy, the risk for a daughter’s subsequent postterm pregnancy → increased two- to threefold

Postterm Pregnancy

Incidence

Postterm Pregnancy

Etiology

Genetic factor : maternal genes influenced prolonged pregnancy

Fetal-placental factors- anencephaly- adrenal hypoplasia- X-linked placental sulfatase deficiency⇒ A lack of the usually high estrogen levels of normal pregnancy

Reduced cervical nitric oxide (NO) release

Incidence

Postterm Pregnancy

Perinatal mortality

Postterm Pregnancy

The major causes of increased perinatal mortality ( Lucas and co-workers ,1965 )

Pregnancy hypertension Prolonged labor with cephalopelvic disproportion Intrapartum asphyxia Meconium aspiration syndrome Shoulder dystocia and macrosomia Unexplained anoxia Malformation ( i.e., anencephaly, adrenal hypoplasia )

Pathophysiology

Postterm Pregnancy

Perinatal mortality

Postterm Pregnancy

Perinatal mortality

Postterm Pregnancy

Postmaturity syndrome Postmature infant’s unique & ch

aracteristic appearances by pathologically prolonged pregnancy

Wrinked, patchy, peeling skin on the palms and soles

Long, thin body suggesting wasting

Long nails Open-eyed, unusually alert, old

& worried-looking face

Incidence : 10% of pregnancies between 41and 43 weeks

Pathophysiology

Placental dysfunction

Clifford (1954) Proposed the skin change of postmaturity were due to loss of the p

rotective effects of vernix caseosa

Stage of postmaturity Stage I : clear AF Stage II : skin was stained green Stage III : skin discoloration – yellow green

Attributed the postmaturity syndrome to placental senescence, although did not find placental degeneration histologically

Postterm Pregnancy

Pathophysiology

Placental dysfunction

Jazayeri and co-workers (1998)

Investigated cord erythropoietin levels in 124 appropriately grown newborns delivered from 37 to 43 weeks

To assess whether fetal oxygenation was compromised due to placental aging in postterm pregnancies

Decreased partial oxygen pressure is the only known stimulator of erythropoietin

Cord erythropoietin levels → significantly increased in pregnancies reaching 41 weeks or more

Postterm Pregnancy

Pathophysiology

Placental dysfunction

The postterm fetus may continue to gain weight, and thus be an unusually large infant at birth

This at least suggests that placental function is not compromised

Indeed, continued fetal growth, although at a slower rate, is characteristic between 38 and 42 weeks

Postterm Pregnancy

Pathophysiology

Postterm Pregnancy

Pathophysiology

Fetal distress and oligohydramnios

Leveno and associates (1984)

Antepartum fetal jeopardy & intrapartum fetal distress → consequence of cord compression associated with oligohydramnios In their analysis of 727 postterm pregnancies, intrapartum fetal distress de

tected with electronic monitoring was not associated with late decelerations characteristic of uteroplacental insufficiency

One or more prolonged decelerations proceeded three fourths of emergency cesarean deliveries for fetal jeopardy

In all but two cases, there were also variable decelerations Another common fetal heart rate pattern was the saltatory baseline

Postterm Pregnancy

Pathophysiology

Postterm Pregnancy

Pathophysiology

Postterm Pregnancy

Pathophysiology

Postterm Pregnancy

Pathophysiology

Postterm Pregnancy

< Saltatory pattern with wide variability > The oscillations of the fetal heart rate above and below the baseline exceed 25 bpm

Pathophysiology

Fetal distress and oligohydramnios

Decreased amnionic fluid volume commonly develops as pregnancy advances beyond 42 weeks

Meconium release into an already reduced amnionic fluid volume → causes thick, viscous meconium → implicated in meconium aspiration syndrome

Postterm Pregnancy

Pathophysiology

Postterm Pregnancy

Pathophysiology

Fetal growth restriction

Divon and co-authors (1998) and Clausson and co-workers (1999) analyzed births of almost 700,000 women between 1991 and 1995 using the National Swedish Medical Birth registry

Stillbirths were more common among growth-restricted infants who were delivered at 42 weeks or beyond

Indeed, one third of the postterm stillbirths were growth restricted

Postterm Pregnancy

Pathophysiology

Postterm Pregnancy

Pathophysiology

Management

Major issue

Whether to intervene at 41 or 42 weeks

Whether labor induction is warranted compared with expectant management using antepartum fetal testing

Roussis and colleague (1993) Two thirds of respondents induced labor at 41 weeks if the cervix was favorable Antepartum fetal testing was advocated beginning at 41weeks when the cervix was unfavorable

Postterm Pregnancy

Management

Unfavorable cervix : It is difficult to precisely define in prolonged pregnancies

Harris and colleagues (1983) A Bishop score of less than 7

Hannah and colleagues (1992) Undilated cervix

Alexander and associates (2000) Women in whom there was no cervical dilatation had a twofold increased ce

sarean delivery rate for “dystocia”

Yang and co-worker (2004) Cervical length of 3cm or less → predictive successful induction

Postterm Pregnancy

Management

Unfavorable cervix Prostaglandin E2

The American college of obstetrician and Gynecologists (1997) → Prostaglandin gel can be safely in postterm pregnancy Use of PG for cervical ripening is discussed

Sweeping of stripping of the membranes Boulvain and co-authors (1999) → At 38 to 40 weeks decreased the frequency of postterm pregnancy → Not modify the risk for cesarean delivery

Station of the vertex The cesarean delivery rate directly related to station 6% if the vertex was -1, 20% at -2, 43% at -3, and 77% at-4

Postterm Pregnancy

Management

Induction versus fetal testing Hannah and colleagues (1992)

Labor induction resulted in a significantly lower cesarean rate (21%) compared with pregnancies managed with antepartum testing (24%)

Menticoglou and Hall (2002) Lamented that induction of labor at 41 weeks has become standard of care of care in Canada Because it caused interference that had the potential to do more harm than good & have staggering resource implications

Alexander and colleagues (2001, at Parkland Hospital) Rates of cesarean delivery significantly increased in the induced group because of failure to progress compared with spontaneous labor (19 versus 14%) Risk factors : nulliparity, unfavorable cervix & eipdural analgesia

Postterm Pregnancy

Management

Induction versus fetal testing

Evidence to substantiate intervention-whether induction or fetal testing-commencing at 41 versus 42 weeks is limited

Usher and colleagues (1988)

Perinatal death rates, corrected for malformations → 1.5, 0.7, and 3.0 per 1000 for 40, 41, and 42 weeks

Based on results summarized in Table 37-1, 41-week pregnancies without other complications such as HTN → considered normal pregnancies at Parkland Hospital

Postterm Pregnancy

Management

Oligohydramnios

When amnionic fluid is decreased in a postterm pregnancy-or for that matter in any pregnancy-the fetus is at increased risk

The smaller the amnionic fluid pocket, the greater the likelihood that there was clinically significant oligohydramnios

Amnionic fluid index (AFI) overestimated the number of abnormal outcomes in postterm pregnancies

Regardless of the criteria used to diagnosis oligohydramnios → increased incidence of “fetal distress” during labor

Postterm Pregnancy

Management

Postterm Pregnancy

Management

Macrosomia

Incidence of macrosomia (defined as birthweight greater than 4500g) → increases from 1.4 % at 37 to 41 weeks to 2.2 % at 42 weeks or more (Marin and colleagues, 2002)

Current evidence doesn’t support a policy of early labor induction in women at term who have suspected fetal macrosomia

Cesarean delivery recommended for estimated fetal weights greater than 4500g in the presence of a prolonged second- stage labor or a second-stage arrest of descent

Postterm Pregnancy

Management

Recommendations of the ACOG (the American College of Obstetricians and Gynecologists)

Although providing flexibility in the evaluation & management of pregnancies completing 42weeks → Antenatal testing or labor induction should be commenced

Postterm pregnancy has been identified as high-risk condition → twice-weekly antepartum fetal testing may be indicated

Oligohydramnios defined as no vertical pocket of amnionic fluid greater than 2 cm or an AFI of 5 cm or less → indication for either delivery or close fetal suveillance

Postterm Pregnancy

Management

Postterm Pregnancy

Management

Management at Parkland Hospital

In women with a certain gestational age, labor is induced at the

completion of 42 weeks

90% of such women are induced successfully

For those who do not deliver with the first induction → a second induction is performed within 3 days

If not delivered, management decisions involve → a third (or more) induction versus cesarean delivery

Postterm Pregnancy

Management

Management at Parkland Hospital

Women classified having uncertain postterm pregnancies are followed on a weekly basis & without intervention unless fetal jeopardy is suspected

Decreased amnionic fluid volume & diminished fetal movement→ Labor induction as described previously for the woman with a certain postterm gestation

Postterm Pregnancy

Management

Medical or Obstetrical Complications

In the event of a medical or obstetrical complications → unwise to allow a pregnancy to continue past 42

weeks

In many such instances early delivery is indicated

Common examples Hypertensive disorders due to pregnancy Prior cesarean delivery Diabetes

Postterm Pregnancy

Management

Intrapartum Management

While being observed for possible labor → Continuous electronic monitoring for variations consistent with fetal distress (American College of Obstetricians and Gynecologists, 1995)

Amniotomy

Reduction in fluid volume → the possibility of cord compression Diagnosis of thick meconium to be dangerous to the fetus if aspirated Scalp electrode and intrauterine pressure catheter can be placed

Postterm Pregnancy

Management

Intrapartum Management

The viscosity of thick meconium

Signifies the lack of liquid & oligohydramnios

Aspiration of thick meconium → severe pulmonary dysfunction & neonatal death

Amnioinfusion during labor as a way of diluting meconium to decrease the incidence of meconium aspiration syndrome

Postterm Pregnancy

Management

Intrapartum Management

The viscosity of thick meconium

The likelihood of a successful vaginal delivery is reduced appreciably for the nulliparous woman who is in early labor with thick, meconium- stained amnionic fluid

When the woman remote from delivery → prompt cesarean delivery, especially when cephalopelvic disproportion is suspected or either hypertonic or hypertonic dysfunctional labor is evident

Postterm Pregnancy

Management

Intrapartum Management

Aspiration of meconium

Suction of the pharynx as soon as the head is delivered

If meconium is identified , the trachea should be aspirated as soon as possible after delivery

The infant should ventilated as needed

Postterm Pregnancy

Management