1. Chapter 37 Postterm Pregnancy
Williams Obstetrics
Chapter 37 Postterm Pregnancy
OBGY R1 Lee Eun Suk

2. 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

3. 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 the 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

4. 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 truly
prolonged, all pregnancies judged to be 42 completed weeks
should be managed as if abnormally prolonged

5. Incidence
Postterm Pregnancy

6. Postterm Pregnancy Maternal demographic factors
Incidence
Postterm Pregnancy
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

7. Postterm Pregnancy Etiology
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

8. Perinatal mortality
Postterm Pregnancy

9. Postterm Pregnancy The major causes of increased perinatal mortality
Pathophysiology
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 )

10. Perinatal mortality
Postterm Pregnancy

11. Perinatal mortality
Postterm Pregnancy

12. Postterm Pregnancy Postmaturity syndrome
Pathophysiology
Postterm Pregnancy
Postmaturity syndrome
Postmature infant’s unique & characteristic 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

13. Postterm Pregnancy Placental dysfunction Clifford (1954)
Pathophysiology
Postterm Pregnancy
Placental dysfunction
Clifford (1954)
Proposed the skin change of postmaturity were due to loss of the protective 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

14. Postterm Pregnancy Placental dysfunction
Pathophysiology
Postterm Pregnancy
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

15. Postterm Pregnancy Placental dysfunction
Pathophysiology
Postterm Pregnancy
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

16. Pathophysiology
Postterm Pregnancy

17. Postterm Pregnancy Fetal distress and oligohydramnios
Pathophysiology
Postterm Pregnancy
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 detected 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

18. Pathophysiology
Postterm Pregnancy

19. Pathophysiology
Postterm Pregnancy

20. Pathophysiology
Postterm Pregnancy

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

22. Postterm Pregnancy Fetal distress and oligohydramnios
Pathophysiology
Postterm Pregnancy
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

23. Pathophysiology
Postterm Pregnancy

24. Postterm Pregnancy Fetal growth restriction
Pathophysiology
Postterm Pregnancy
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

25. Pathophysiology
Postterm Pregnancy

26. Management

27. Postterm Pregnancy Major issue Whether to intervene at 41 or 42 weeks
Management
Postterm Pregnancy
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

28. Postterm Pregnancy Unfavorable cervix
Management
Postterm Pregnancy
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 cesarean delivery rate for “dystocia”
Yang and co-worker (2004)
Cervical length of 3cm or less → predictive successful induction

29. Postterm Pregnancy Unfavorable cervix Prostaglandin E2
Management
Postterm Pregnancy
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

30. Postterm Pregnancy Induction versus fetal testing
Management
Postterm Pregnancy
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

31. Postterm Pregnancy Induction versus fetal testing
Management
Postterm Pregnancy
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

32. Postterm Pregnancy Oligohydramnios
Management
Postterm Pregnancy
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

33. Management
Postterm Pregnancy

34. Postterm Pregnancy Macrosomia
Management
Postterm Pregnancy
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

35. Postterm Pregnancy Recommendations of the ACOG
Management
Postterm Pregnancy
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

36. Management
Postterm Pregnancy

37. Postterm Pregnancy 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

38. Postterm Pregnancy 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

39. Postterm Pregnancy Medical or Obstetrical Complications
Management
Postterm Pregnancy
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

40. Postterm Pregnancy 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

41. Postterm Pregnancy 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

42. Postterm Pregnancy 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

43. Postterm Pregnancy 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