Chapter 37 Postterm Pregnancy

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

22. 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. 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. 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. 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. 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. 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. 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 3.0per 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. 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. 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. 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. Management Postterm Pregnancy • Management at Parkland Hospital • In women with a certaingestational 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. Management 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. 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. Management 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. Management 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. Management 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. Management 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