Gestational age at deliverya 35.1 ± 3.3 39.2 ± 2.0 <.001 Preterm birth, spontaneousa 49 (42) 1698 (6) <.001
Preterm birth, indicateda 20) 405 (2) <.001
Cesarean delivery for nonreassuring 10l(9) 1083 (4) <.001
Birthweight < 10th percentilea 61 (53) 3388 (12) <.001 <3rd percentilea 43 (37) 1130 (4) <.001 1) <.OOllb
Data expressed as No. (%) and mean ± standard deviation. aAnomalous infants excluded.
bThis difference was no longer significant after adjustment for gestational age at delivery. Data from 2011.
complicated 2 percent of pregnancies undergoing sonography at Parkland Hospital ater 34 weeks' gestation. Fetal malformation rates were elevated in those with oligohydramnios. Even in their absence, rates of stillbirth, growth restriction, nonreassUfing heart rate pattern, and meconium aspiration syndrome were higher than in nonafected pregnancies. Petrozella and associates (2011) similarly reported that an AFI :;5 em identiied between 24 and 34 weeks was associated with increased risks for stillbirth, spontaneous or medically indicated preterm birth, heart rate pattern abnormalities, and growth restriction (see Table 11-4). In one metaanalysis comprising more than 10,000 pregnancies, women with oligohydramnios had a twofold greater risk for cesarean delivery for fetal distress and a ivefold higher risk for an Apgar score <7 at 5 minutes compared with pregnancies with a normal AFI (Chauhan, 1999).
As discussed, evidence suggests that if oligohydramnios is defined as an AFI :;5 em rather than a single deepest pocket :;2 em, more pregnancies will be classiied as such. One review of trials encompassing more than 3200 high-risk and low-risk pregnancies compared outcomes according to which deinition was used (Nabhan, 2008). Rates of cesarean delivery, neonatal intensive care unit admission, umbilical artery pH <7.1, or Apgar score <7 at 5 minutes did not difer between groups. Using AFI criteria, however, twice as many pregnancies were diagnosed with oligohydramnios. In this group, there was a doubling of the labor induction rate and a 50-percent increase in the cesarean delivery rate for fetal distress. Kehl and colleagues (2016) performed a prospective trial with more than 1000 term pregnancies in which women with oligohydramnios, deined either by an AFI < 5 em or a single deepest pocket <2 em, were randomized to labor induction or expectant care. Signiicantly more pregnancies were diagnosed with oligohydramnios using the AFI criterion-10 percent compared with just 2 percent-when single deepest pocket was used. This led to a higher rate of labor induction in the AFI group, but no diference in neonatal outcomes.