Chapter 32Post-term Pregnancy Jamie L. Resnik, MD, and Robert Resnik, MDIn 1902, Ballantyne1 described the problem of the post-term pregnancy screening examination performed between 17 and 22 weeks’ gestationfor the ﬁrst time in modern obstetric terms. Although the language was reported in one recent study to be more accurate in predicting theused to describe the entity in early 20th-century Scotland was different delivery date than a ﬁrst-trimester screen,5 most reports have tendedfrom that of today, Ballantyne’s words clearly reﬂected the thinking of to agree with the ﬁndings of Bennett and associates.6 These authorshis time: “The postmature infant . . . has stayed too long in intrauterine randomly assigned women to either a ﬁrst-trimester (n = 104) or asurroundings; he has remained so long in utero that his difﬁculty is second-trimester (n = 92) ultrasound examination; 5 of the women into be born with safety to himself and his mother. The problem of the ﬁrst group underwent labor induction for a post-term gestation,the . . . postmature infant is intranatal.” compared with 12 of those in the second group. In any case, it is clear During the ensuing years, the issue of post-term pregnancy, its that use of the LMP alone tends to substantially overestimate therisks, and its management generated great interest and controversy. An number of post-term gestations and that the widespread use of ﬁrst-abundance of older as well as more recent data have ﬁrmly established trimester ultrasound examinations, now used for noninvasive geneticthat the fetal risk associated with a prolonged pregnancy is real, albeit screening, will have a great impact on the diagnosis and subsequentsmall. Consequently, the pregnancy that continues beyond 42 weeks management of this entity.requires careful surveillance. PathogenesisDeﬁnition and Incidence Knowledge of the mechanism of parturition is increasing rapidly, andBy deﬁnition, a term gestation is one that is completed in 37 to 42 the current understanding of the pertinent molecular, biochemical,weeks. Pregnancy is considered prolonged, or post-term, when it and physiologic ﬁndings are reviewed in Chapter 5. It is clear that theexceeds 294 days from the last menstrual period (LMP), or 42 weeks. normal timing of parturition requires the integration and synchronyThe frequency of this occurrence has been reported to range from 4% of numerous factors, including the fetal hypothalamic-pituitary-to 14%, with only 2% to 7% of pregnancies completing 43 weeks. The adrenal axis, the placenta and its membranes, and the myometriumchances that parturition will occur precisely at 280 days after the ﬁrst and cervix. Although it is not known speciﬁcally why some pregnanciesday of the LMP (40 weeks) is only 5%. are abnormally prolonged, clues exist from interesting observations of One of the major problems in delineating the extent of risk beyond aberrant timing of labor in humans and other species. For example,term is the limited reliability of the LMP as a basis for accurately pre- it has long been known that fetal pituitary defects in Holstein cattledicting gestational age. Traditionally, and until the 1990s, most epide- may lead to failure of normal delivery timing.7 In humans, congenitalmiologic studies pertaining to fetal and neonatal risks of delayed primary fetal adrenal hypoplasia and placental sulfatase deﬁciencyparturition were based on the LMP. Since that time, the use of ultra- leading to low estrogen production may result in delayed onset of laborsound, particularly in the ﬁrst trimester, has led to much greater preci- and failure of normal cervical ripening.8,9sion in pregnancy dating, and data conﬁrm that the LMP is a much Whether the primary defect in delayed parturition involves aberra-less reliable predictor of true gestational age. For example, as early as tions in fetal endocrine signaling or abnormalities in the setting of the1988, Boyd and colleagues2 showed that the incidence of post-term “placental clock” (as was suggested by McLean and colleagues10), orgestation fell from 7.5% when based on menstrual dating to 2.6% whether the myometrial contractile and cervical softening mechanismswhen early ultrasound examination was used. In a subsequent study are at fault, it is clear from the abundant data currently available thatby Gardosi and colleagues,3 the post-term delivery rate among women the timing of parturition is determined by complex interactions at thedated by LMP was 9.5% but decreased to 1.5% if ultrasound dating maternal-fetal interface.was used. In their study, 71.5% of “post-term” inductions as dated byLMP were not post-term according to ultrasound studies. This ﬁndingis consistent with the observations of Taipale and Hiilesmaa,4 whoperformed ultrasound examinations at 8 to 16 weeks’ gestation in Risk Factors17,221 women. When ultrasound biometric criteria rather than the Primiparity has long been known to be more frequently associatedLMP were used to determine gestational age, the number of post-term with post-term gestation than multiparity. However, there also appearspregnancies fell from 10.3% to 2.7%. Although a second-trimester to be an increased frequency of recurrence among women who have
614 CHAPTER 32 Post-term Pregnancyhad a previous post-term pregnancy. One large cohort study from 6Denmark has demonstrated that women who delivered post-term in Stillbirththeir ﬁrst pregnancy had an almost threefold increase in the incidence Neonatal deathof subsequent post-term pregnancy, compared with those whose ﬁrst Postneonatal deathdelivery was at term.11 These ﬁndings were recently conﬁrmed by 5Kistka and coworkers12 in a study of 368,633 births in Missouri, in Mortality per 1000 ongoing pregnancieswhich mothers with an initial post-term birth were at increased riskfor a subsequent post-term pregnancy (relative risk [RR], 1.88; 95%conﬁdence interval [CI], 1.79 to 1.97). These ﬁndings also suggest the 4possibility of a genetic predisposition, inasmuch as the risk of recur-rent post-term pregnancy in the Danish study was not observed if theﬁrst and second children had different fathers. 3Perinatal Risks 2Morbidity and MortalityAlmost all reports up to the present time, even those with inherentlimitations imposed by inaccuracies in gestational age determination, 1suggest an increase in perinatal morbidity and mortality when preg-nancy goes beyond 42 weeks’ gestation. One of the earliest and mostfrequently cited studies was provided by the National Birthday Trust 0of Britain in 1958, which undertook a detailed examination of more 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43than 17,000 births in the United Kingdom from March 3 to March 9 Gestational age (weeks)of that year.13 Their data demonstrated that the perinatal mortality ratebegan to increase after 42 weeks’ gestation, doubling by about 43 weeks, FIGURE 32-1 Perinatal mortality as a function of gestational age.and was four to six times higher at 44 weeks than at term. A more The rates of stillbirth, neonatal, and postneonatal death increase with advancing gestational age beyond 41 weeks. The perinatal mortalityrecent study showed that the risks begin to accelerate between 41 and is expressed per 1000 ongoing pregnancies. (From Hilder L, Costeloe42 weeks and rise more sharply after that point (Fig. 32-1).14 Numerous K, Thilaganathan B: Prolonged pregnancy: Evaluating gestation-other reports have conﬁrmed this increase in risk.15-17 Alexander and speciﬁc risks of fetal and infant mortality. BJOG 1998;105:169-173.)associates18 retrospectively evaluated outcomes of more than 27,000pregnancies with 41 or 42 weeks’ gestation, compared with approxi-mately 29,000 completed at 40 weeks’ gestation. Length of labor, inci-dence of prolonged second-stage labor, forceps use, and cesarean pared with term infants,17,23 and birth injuries can occur as a result ofdelivery were all increased with the longer gestation period. It is not difﬁcult forceps deliveries and shoulder dystocia. Morbidity alsoclear, however, whether the observed increase in complications was due includes cephalohematomas, fractures, and brachial plexus palsy.24to prolonged gestation, routine use of induction at 42 weeks, or Study of fetal growth characteristics in 7000 post-term infants con-both. ﬁrmed a gradual shift toward higher birth weights and greater head In a more recent Norwegian study, in which 17,493 pregnancies circumference between 273 and 300 days of gestational age.25 Thesewith conﬁrmed dates by second-trimester ultrasound were analyzed, ﬁndings were further reinforced by a study of 519 pregnancies extend-1336 were found to be post-term. The post-term group had twice the ing beyond 41 weeks, in which 23% of the newborns weighed moreperinatal mortality rate (CI, 0.9 to 4.6); the RR of having an Apgar than 4000 g and 4% weighed more than 4500 g.26score lower than 7 at 5 minutes was 2.0 (CI, 1.2 to 3.3), and the RR of Although the majority of post-term infants are appropriately grownrequiring neonatal intensive care was 1.6 (CI, 1.3 to 2.0).19 Another or macrosomic, the risk of a small-for-gestational-age (SGA) infant isprospective cohort study of 27,514 pregnancies from the same country also increased in post-term pregnancy. In a population-based study ofdemonstrated that maternal and fetal risks were lowest at 39 weeks’ 510,029 singleton pregnancies from the Swedish Birth Registry, the rategestation, with increasing rates of maternal and neonatal complica- of SGA infants increased from 2.2% in term infants to 3.8% in post-tions, as well as operative deliveries, as pregnancy proceeded past term infants.27term.20 Similar ﬁndings were reported in a Danish population.21 Meconium Staining andAbnormal Fetal Growth Pulmonary AspirationSince the report of Clifford22 and his description of the postmature- Almost all studies of post-term gestation report a markedly higherdysmature neonate with wasting of subcutaneous tissue, meconium incidence of meconium-stained amniotic ﬂuid, compared with termstaining, and peeling of skin, many have focused their attention on the pregnancies, and the greater risk of meconium aspiration syndrome inproblems of the undernourished post-term fetus. In fact, only 10% to these infants is well recognized.17 Among those infants deﬁned by20% of true post-term fetuses exhibit any of the ﬁndings described by ultrasound-estimated fetal growth curves to be appropriately sized forClifford. Macrosomia is actually a far more common complication, gestational age (AGA), those delivered post-term had a threefold higherbecause, under most circumstances, the fetus continues to grow in incidence of meconium aspiration and twice the risk of an Apgar scoreutero. Twice as many post-term fetuses weigh more than 4000 g, com- of less than 4 at 5 minutes, compared with term AGA infants.27 The
CHAPTER 32 Post-term Pregnancy 615presence of oligohydramnios further complicates the risks of meco- However, a cohort study done in Sweden showed no correlationnium staining because of the lack of ﬂuid to dilute the meconium, between an AFI of less than 5 cm and adverse outcome.38 Similarly,which results in thicker, more tenacious material in the oropharynx Divon and associates,39 in a longitudinal assessment of AFI in 139and lower in the respiratory tract. women with post-term pregnancy, found an increased frequency of abnormal fetal heart rate tracings and meconium staining but no other signiﬁcant adverse fetal outcome. Alﬁrevic and colleagues40 compared both methods with respect to pregnancy intervention in post-termFetal Evaluation and pregnancies and found more frequent abnormal AFIs than abnormalManagement vertical pocket depths, leading to more inductions and fetal monitor- ing but no difference in perinatal outcome. Morris and colleagues41When one considers the rapidly accelerating risk of fetal morbidity and conducted a prospective, double-blinded, cohort study to determinemortality between 42 and 43 weeks’ gestation and again between 43 whether an AFI of less than 5 cm or a single vertical pocket of less thanand 44 weeks’ gestation (see Fig. 32-1), it becomes apparent that no 2 cm was superior in predicting adverse perinatal events. They foundhistorically derived or laboratory-measured fetal age provides the pre- the AFI to be signiﬁcantly more associated with birth asphyxia andcision required in the management of the post-term pregnancy. Tra- meconium aspiration, but with poor sensitivity. More recently, Zhangditional landmarks, such as LMP, uterine size, and ﬁrst auscultation of and associates,42 using data from the Routine Antenatal Diagnosticfetal heart tones, can miscalculate gestational age by 2 weeks or more. Imaging with Ultrasound (RADIUS) study, compared a large popula-Even sensitive sonographic determinations, such as crown-to-rump tion of women screened by ultrasound to control subjects and observedlength in the ﬁrst trimester, demonstrate a range of several days. In that women with isolated oligohydramnios had no greater adversefact, in any given gestation, the actual fetal age is known only if the perinatal events or impaired growth. Another study comparing the twotime of ovulation and conception have been studied, as in ovulation techniques showed that the single vertical pocket method used forinduction and in vitro fertilization. Therefore, a gravida thought to be antepartum surveillance led to less frequent diagnosis and interventionat 41 to 42 weeks or further in gestation, in current practice, either for oligohydramnios, but without any difference in adverse perinatalis induced and delivered or undergoes meticulous antenatal outcomes.43monitoring. Given these disparate ﬁndings, it is not difﬁcult to understand why there is no consensus as to the reliability or superiority of either tech- nique for identiﬁcation of the fetus at risk in prolonged pregnancy.Antenatal Fetal Monitoring Therefore, it is reasonable to conclude that an AFI of less than 5 cm,Despite the lack of randomized clinical trials, it is generally accepted particularly if it has been falling sharply over a short time interval, orthat careful antepartum and intrapartum fetal monitoring can virtu- the absence of a single identiﬁable vertical pocket of greater than 2 cm,ally eliminate fetal post-term mortality and reduce fetal morbidity.28-32 indicates that delivery is warranted. Conversely, it is also reasonable toHowever, a careful evidence-based literature analysis concluded that consider that the ﬁnding of a normal amniotic ﬂuid volume impliesdata were insufﬁcient to determine whether routine antenatal surveil- little fetal risk.lance before 41 weeks’ gestation improves outcome or which type of There does not appear to be any value in monitoring Doppler ﬂowmonitoring and frequency are most appropriate.33 Consequently, most velocity in fetal vessels, inasmuch as there is no correlation betweenobstetricians initiate antenatal testing at 41 weeks’ gestation and repeat the ﬁndings and outcome.44 Zimmerman and associates45 demon-the testing twice weekly. This testing consists of either a biophysical strated that the sensitivity of umbilical artery velocimetry for predict-proﬁle (BPP) or a nonstress test and assessment of amniotic ﬂuid ing poor outcome was 7%.volume. In a study of 307 women whose pregnancies had proceeded beyond294 days, a normal twice-weekly BPP that included normal amniotic Fetal Monitoring versusﬂuid volume resulted in no perinatal mortalities, and morbidity was Induction of Laborequivalent to that observed in a comparison group undergoing elective Even though antenatal monitoring can virtually eliminate perinatallabor induction with a favorable cervix.32 Based on a cumulative expe- mortality in the post-term gestation, some morbidity—includingrience with 19,221 high-risk pregnancies, the same investigative group meconium staining, increased cesarean delivery for a diagnosis of fetalrecommended delivery if amniotic ﬂuid volume decreases.34 distress, and macrosomia with its associated complications—still The technique used to assess amniotic ﬂuid volume and its role in exists. Although the frequency of morbid events is very low, theevaluation of the prolonged gestation remains controversial because of continuing concern has been addressed by an alternative approach—conﬂicting studies regarding which of the two tests of volume (amni- that of cervical ripening followed by induction at 41 or 42 weeks’otic ﬂuid index [AFI] or single vertical pocket) is the better predictor gestation.of outcome and the possibility that the AFI may lead to too many Comparison of these two management approaches in several ran-unnecessary interventions. Oligohydramnios is thought to be a marker domized controlled trials has yielded generally similar results. Hannahfor fetal complications, including umbilical cord compresssion, hypox- and coauthors46 studied 3407 women with uncomplicated pregnanciesemia, and meconium aspiration, as well as fetal heart rate abnormali- at 41 or more weeks’ duration, who were randomly assigned toties and risk of neonatal admission to an intensive care unit.35-37 either elective induction after cervical ripening with prostaglandin E2Bochner and coworkers36 observed an almost 24-fold increase in cesar- (PGE2) gel or serial antenatal monitoring (fetal kicks, nonstress test,ean delivery for the indication of fetal distress when the maximum amniotic ﬂuid). In the monitored group, labor was induced only ifvertical amniotic ﬂuid pocket depth was less than 3 cm. The incidence there was evidence of compromised fetal status. The authors observedof meconium-stained amniotic ﬂuid in the post-term gestation was a lower rate of cesarean delivery for a diagnosis of fetal distress in the37% among those women with adequate amniotic ﬂuid volume but induction group but no signiﬁcant difference between the two groupsincreased to 71% if the amniotic ﬂuid volume was decreased.31 in fetal mortality or morbidity. The same investigators subsequently
616 CHAPTER 32 Post-term Pregnancyreported that routine induction was more cost-effective than serial including a signiﬁcant risk of postpartum hemorrhage and an increasedantenatal monitoring.47 The Maternal-Fetal Medicine Network pro- risk of cesarean delivery.spectively evaluated 440 patients, comparing induction with serial The Bishop score,53 or some suitable modiﬁcation of it, can be usedmonitoring.48 They observed no fetal deaths in either group, and rates as a guide to select the most appropriate induction technique. This isof neonatal morbidity and cesarean delivery were similar. A more especially true in primigravid women. If the Bishop score is lower thanrecent study from Norway, in which 254 women at 41 weeks’ gestation 5, amniotomy and oxytocin infusion are associated with an unaccept-were randomly assigned to an induction or expectant manage- ably high incidence of unsuccessful inductions as well as fetal andment group, found no differences in neonatal outcomes or mode of maternal complications.54 In these circumstances, cervical ripeningdelivery.49 should be undertaken before uterine contractions are provoked. Given These combined trials have led to the conclusion that neither the rapidly increasing use of transvaginal ultrasound (TVUS) to assessapproach has a substantive advantage over the other. A small advantage cervical length and dilatation and its usefulness in the diagnosis ofto the induction approach was suggested by the recent Cochrane preterm labor, it is not unreasonable to apply this technology to cervi-Review of 19 studies, which determined that a policy of labor induc- cal assessment in post-term pregnancy. One study of 240 women,tion at 41 weeks resulted in fewer fetal deaths, although the differences comparing TVUS with digital cervical examination using receiverand absolute risk were extremely small (1 in 2986 versus 9 in 2953; operating characteristic (ROC) curves, demonstrated that a cervicalodds ratio, 0.3; CI, 0.9 to 0.99). There was no signiﬁcant difference in length of 28 mm was a better predictor of induction success (vaginalthe cesarean section rate.50 delivery within 24 hours) than the Bishop score.55 However, conﬂicting Nevertheless, in terms of physician preferences in the United States, ﬁndings were reported by Chandra and associates.56induction at 41 weeks has become the mode of practice and the debate The most frequently used current cervical ripening techniquesmoot. A recent survey of 1000 randomly selected members of the include chemical agents such as PGE2 (dinoprostone, trade namesAmerican College of Obstetricians and Gynecologists revealed that Prepidil and Cervidil Rx), administered vaginally or intracervically,73% routinely induce low-risk women at 41 weeks. For women who and misoprostol (Cytotec Rx), administered vaginally or orally. Bothdecline induction, approximately 65% of physicians initiate antenatal appear to be effective in improving the Bishop score and to result intesting twice weekly at 41 weeks.51 It is clear that medical induction shorter labor times and possibly fewer failed inductions. Misoprostol,rates have increased sharply in the United States. Between 1980 and in doses of 25 μg given vaginally every 4 hours, appears to be slightly1996, the rate of induction doubled (from 12.9% to 25.8%), the most more effective that dinoprostone but is associated with a higher fre-common indication being that of the post-term pregnancy.52 quency of uterine tachysystole. A recent review of randomized trials performed between 1987 and 2005 compared the two agents and con- ﬁrmed that misoprostol was superior to dinoprostone at any dose andManagement Summary route of administration in terms of achieving vaginal delivery withinIt seems appropriate to recommend the following steps to evaluate and 24 hours. There was no difference in the rate of cesarean delivery.57manage the post-term gestation: This study conﬁrmed an earlier Cochrane database review which con- cluded that the use of vaginal misoprostol is more effective than con-1. Although there is insufﬁcient evidence because of the low-risk ventional methods of cervical ripening and labor induction. Compared nature of either approach, current obstetric practice dictates that with placebo, oxytocin, or intracervical or vaginal PGE2, misoprostol labor induction be offered between 41 and 42 weeks’ gestation in resulted in increased cervical ripening, decreased use of oxytocin, and the presence of a favorable cervix. increased rates of vaginal delivery. However, misoprostol also caused2. If the cervix is unfavorable, alternate approaches include either an increased rate of uterine hyperstimulation.58 cervical ripening followed by induction of labor or twice-weekly Vaginal inserts such as balloon catheters also have their advocates fetal monitoring. Delivery should be accomplished promptly if for cervical ripening. A systematic review concluded that these mechan- there is evidence of fetal compromise. ical dilators do not compare favorably with chemical inducing agents3. It is prudent to use the BPP, or some modiﬁcation of the BPP, to in terms of delivery success rates but are associated with less uterine determine antenatal fetal condition. hypercontactility.59Methods of Labor Induction Developmental Effects ofThe issue of labor induction and cervical ripening agents is addressedin detail in Chapter 36 and is summarized brieﬂy here. Post-term Gestation Because normal labor depends on efﬁcient myometrial contrac- Studies on the development of children from prolonged pregnanciestions acting on a compliant cervix to efface and dilate it, methods of are difﬁcult to evaluate because investigators have not separated neo-labor induction must take into account both components of the uterus. nates asphyxiated in utero and growth-restricted (dysmature) post-If the cervix is already soft, effaced, and partially dilated, intravenous term neonates from otherwise normally born neonates. A study ofinfusion of oxytocin may be sufﬁcient to stimulate contractions. Con- neonatal behavior among 106 dysmature infants revealed an increasedventional practice requires amniotomy to be performed as a ﬁrst step, number of illnesses and sleep disorders as well as diminished socialbecause this procedure maximizes the effectiveness of oxytocin. If the competence during the ﬁrst year of life (Vineland Social Maturitycervix is unripe, oxytocin will not cause it to ripen, and amniotomy Scale). Also, and not unexpectedly, the incidence of fetal distress wasis inappropriate. Although labor contractions can be stimulated by high, and those babies who were asphyxiated in utero had a higheroxytocin, such a result is futile, because many hours of such contrac- incidence of abnormal neurologic signs in the neonatal period.60 Alltions are required to produce any sort of change in the cervix, and the infants had signs of desquamation of skin and wasting of subcutaneousensuing prolonged labor can lead to an increase in obstetric morbidity, tissue, however, and the group of children studied was not compared
CHAPTER 32 Post-term Pregnancy 617with any post-term children who did not have these physical ﬁndings 14. Hilder L, Costeloe K, Thilaganathan B: Prolonged pregnancy: Evaluatingat birth. gestation-speciﬁc risks of fetal and infant mortality. BJOG 105:169-173, Field and coworkers61 studied a group of 40 dysmature offspring, 1998.all of whom had parchment-like skin and long, thin bodies. At birth, 15. Nakano R: Post-term pregnancy: A ﬁve year review from Osaka National Hospital. Acta Obstet Gynecol Scand 51:217, 1972.their Brazelton interaction and motor scores were lower than in 16. Sachs BP, Friedman EA: Results of an epidemiological study of post-dateterm controls, and at 4 months they scored lower on the Denver pregnancy. J Reprod Med 31:162, 1986.Developmental Scale. By 8 months, the Bayley motor scores of the 17. Eden R, Seifert L, Winegar A, et al: Perinatal characteristics of uncompli-post-term subjects were equivalent to those of control infants, but their cated post-date pregnancies. Obstet Gynecol 69:296, 1987.mental scores were slightly lower. This study differed in at least one 18. Alexander JM, McIntire DD, Leveno UJ: Forty weeks and beyond:signiﬁcant way from that of Lovell60: The Apgar scores at 5 minutes in Pregnancy outcomes by week of gestation. Obstet Gynecol 96:291, 2000.the two groups were identical, thus partially correcting for in utero 19. Nakling J, Backe B: Pregnancy risk increases from 41 weeks of gestation.asphyxia. Acta Obstet Gynecol 85:663-668, 2006. In a large retrospective review, Zwerdling23 observed that post-term 20. Heimstad R, Romundstad PR, Eik-Nes SH, et al: Outcomes of pregnanciesinfants weighing less than 2500 g had a neonatal mortality rate seven beyond 37 weeks of gestation. Obstet Gynecol 108:500-508, 2006. 21. Olesen AW, Westergaard JG, Olsen J: Perinatal and maternal complicationstimes that of post-term infants as a whole. This ﬁnding conﬁrmed the related to post-term delivery: A national regiser-based study, 1978-1993.additional risk of the dysmature growth pattern in some post-term Am J Obstet Gynecol 189:222-227, 2003.infants. The increased mortality rate was observed up to 2 years of age, 22. Clifford SH: Postmaturity—with placental dysfunction. J Pediatr 44:1, 1954.but at 5 years the data on growth and intelligence in Zwerdling’s study 23. Zwerdling MA: Factors pertaining to prolonged pregnancy and its outcome.population revealed no differences between prolonged-gestation and Pediatrics 40:202, 1967.normal-gestation children. These ﬁndings were conﬁrmed in a pro- 24. Usher RH, Boyd ME, McLean FH, et al: Assessment of fetal risk in post-datespective study in which 129 children born of prolonged pregnancy pregnancies. Am J Obstet Gynecol 158:259, 1988.were compared with 184 term controls.62 At 1 year and again at 2 years 25. McLean FH, Boyd ME, Usher RH: Post-term infants: Too big or too small?of age, there were no differences between the two groups with respect Am J Obstet Gynecol 164:619, 1991.to intelligence scores, physical milestones, or intercurrent illnesses. 26. Pollack RN, Hauer-Pollack G, Divon MY: Macrosomia in post-dates preg- nancy: The accuracy of routine ultrasonographic screening. Am J Obstet One recent cohort study from Denmark linked hospital records of Gynecol 167:7, 1992.277,435 pregnancies delivering at term or beyond to cases of childhood 27. Clausson B, Cnattingius S, Axelsson O: Outcomes of post-term births: Theepilepsy. The researchers found a slight increase in the incidence of role of fetal growth restriction and malformations. Obstet Gynecol 94:758,epilepsy as a function of gestational age at or after 43 weeks, but only 1999.among those infants delivered by cesarean section or other operative 28. Hauth JC, Goodman MT, Gilstrap LC III, et al: Post-term pregnancy.delivery.63 The risk was not observed after 1 year of life. Whether this J Obstet Gynecol 56:467, 1980.ﬁnding reﬂects a problem unique to advanced gestational age or com- 29. Freeman RK, Garite TJ, Modanlou H, et al: Postdate pregnancy: Utilizationplications that required expedient delivery is unclear. of contraction stress testing for primary fetal surveillance. Am J Obstet Gynecol 140:128, 1981. 30. Eden R, Gergely RZ, Schifrin BS, et al: Comparison of antepartum testing schemes for the management of the postdate pregnancy. Am J ObstetReferences Gynecol 144:683, 1982. 1. Ballantyne JW: The problem of the postmature infant. J Obstet Gynaecol 31. 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Olesen AW, Thomsen SG: Prediction of delivery date by sonography in ington, DC, ACOG, 2004. the ﬁrst and second trimesters. Ultrasound Obstet Gynecol 28:292-297, 34. Manning FA, Morrison I, Harman CR, et al: Fetal assessment based on fetal 2006. biophysical proﬁle scoring: Experience in 19,221 referred high risk preg- 6. Bennett KA, Crane JM, O’Shea P, et al: First trimester ultrasound screening nancies. II: An analysis of false negative deaths. Am J Obstet Gynecol is effective in reducing post-term labor induction rates: A randomized 157:880, 1987. controlled trial. Am J Obstet Gynecol 190:1077-1081, 2004. 35. Leveno KJ, Quirk JG, Cunningham FG, et al: Prolonged pregnancy: I. 7. Holm LW: Prolonged pregnancy. Adv Vet Sci 11:159, 1967. Observations concerning the causes of fetal distress. Am J Obstet Gynecol 8. France JT, Liggins GC: Placenta sulfatase deﬁciency. J Clin Endocrinol 150:465, 1984. 29:138, 1969. 36. 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