Rates of stillbirth, neonatal death, and infant morbidity all rise after the expected due date has passed. This is best seen when perinatal mortality rates are analyzed from times before widespread intervention for postterm pregnancies. In two large Swedish studies shown in Figure 43-1, after reaching a nadir at � 7.2 4.0 c 2.32.4 ing to gestational age of all births in Sweden during 1943-1952 compared with those during 1977-1o978. The partially compressed scale is used for convenience in depiction. (Adapted from
Bakketeig, 1991; Lindell, 1956.)
TABLE 43-1 . Adverse Maternal and Perinatal Outcomes Associated with Postterm Pregnancy
NICU = neonatal intensive care unit.
39 to 40 weeks, the perinatal mortality rate rose as pregnancy duration exceeded 41 weeks. his trend is also reported for the United States (Cheng, 2008; MacDorman, 2009). As shown in
Table 43-1, the major cause of death in these studies includes gestational hypertension, prolonged labor with cephalopelvic disproportion, birth injuries, and hypoxic-ischemic encephalopathy. Similar outcomes were reported by Olesen and colleagues (2003) in 78,022 women with postterm pregnancies delivered before routine labor induction was adopted in Denmark. Moster and associates (2010) found higher rates of cerebral palsy in postterm births, and Yang and coworkers (2010) reported lower intelligence quotient (IQ) scores at age 6.5 years in children born :42 weeks' gestation. Conversely, autism was not associated with postterm birth (Gardener, 2011).
Alexander and colleagues (2000a) reviewed 56,317 consecutive singleton pregnancies delivered at :40 weeks between 1988 and 1998 at Parkland Hospital. Labor was induced in 35 percent of pregnancies completing 42 weeks. he rate of cesarean delivery for dystocia and fetal distress was signiicantly greater at 42 weeks compared with earlier deliveries. More newborns of postterm pregnancies were admitted to intensive care units. Importantly, the incidence of neonatal seizures and deaths was doubled at 42 weeks. Smith (2001) has challenged analyses such as these because the population at risk for perinatal mortality in a given week consists ofall ongoing pregnancies rather than just the births in a givenweek. He calculated perinatal mortality rates calculated using only births in a given week of gestation from 37 to 43 completedweeks comparedwith the cumulative probabilitythe perinatal index-of death when all ongoing pregnancies are included in the denominator. Using this computation, delivery at 38 weeks had the lowest risk index for perinatal death.
The postmature newborn is unique, and features include wrinkled, patchy, peeling skin; a long, thin body suggesting wasting; and advanced maturity in that the infant is open-eyed, unusually alert, and appears old and worried 43-2). Skin wrinkling can be particularly prominent on the palms and soles. The nails are typically long. Most postmature neonates are not technically
FIGURE 43-2 Postmaturity syndrome. Neonate delivered at 43 weeks' gestation with thick, viscous meconium coating the desquamating skin. Note the long, thin appearance and wrinkling of the hands.
growth restricted because their birthweight seldom falls below the 10th percentile for gestational age (Chap. 44, p. 847). On the other hand, severe growth restriction-which logically must have preceded completion of 42 weeks-may be present.