Acute oligohydramnios in postdate pregnancy.

The evaluation of amniotic fluid volume plays a major role in antepartum fetal surveillance. Although the definition of diminished amniotic fluid volume varies, this sign is considered by itself an indication for intervention in the near-term fetus. The interval of testing is predicated on the concept that amniotic fluid volume diminishes slowly (unquantified) as a result of developing hypoxia. We present six postterm pregnancies in which amniotic fluid volume diminished abruptly over 24 hours. Although one fetus died, the three babies delivered by cesarean section and the two babies delivered after a 2-day labor did well, despite obvious postmaturity syndrome, meconium staining, and variable decelerations. Apgar scores in the survivors were above 8, and pH results failed to confirm hypoxia. These data suggest the need to better understand the mechanisms regulating amniotic fluid volume.