Oligohydramnios: A Reason to Deliver?

Abtract & Commentary

By John C. Hobbins, MD, Professor of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora, CO, is Associate Editor for OB/GYN Clinical Alert.

Dr. Hobbins reports no financial relationships relevant to this field of study.

Synopsis:A recent study suggested that intervening in isolated oligohydramnios between 35 and 37 weeks is associated with higher rates of inductions, cesarean sections, and preterm birth as compared with expectant management.

Source: Melamed N, et al. Perinatal outcome in pregnancies complicated by isolated oligohydramnios before 37 weeks. Am J Obstet Gynecol 2011;205:241.e1-241.e6.

In an otherwise normal preterm pregnancy, is oligohydramnios a reason to deliver? This question has popped up repeatedly, and an article in the September issue of the American Journal of Obstetrics and Gynecology addressed this conundrum.

In a retrospective study,1 the authors reviewed data from 1996 through 2007 involving patients who had ultrasound evaluations prior to 36 weeks of gestation. Of the 21,718 patients reviewed, 980 (4.5%) were noted to have oligohydramnios (amniotic fluid index [AFI] < 5 cm). Of these, 108 (10.9%) were judged to be "isolated." Each of these patients was compared with three controls who had normal AFIs and were matched for gestational age. The isolated oligohydramnios group then was subdivided into those having intervention vs those having expectant management.

The average age at the time the oligohydramnios was found was 32 weeks in both oligohydramnios groups. In the intervention group, the average gestational age of delivery was 36 weeks vs 38.9 weeks in the expected management group. There were no differences between oligohydramnios and controls regarding the incidence of preeclampsia or intrauterine growth restriction (IUGR), and there were no cases of intrauterine demise in either group. In 10% of the oligohydramnios group, the AFI reverted to normal. In the oligohydramnios group, there was a significantly higher rate of preterm birth (26.9% vs 12.3%), induction of labor (50% vs 5.6%), induction failure (33% vs 6.4%), and cesarean birth (47.2% vs 16.9%). Not surprisingly, there was a higher rate of combined neonatal morbidity.

Interestingly, when comparing the intervention group to the expectant management group, the authors found that the intervention group (78) had higher rates of every morbid outcome (as listed above) compared to the expectant management group (30). Although there was a lower mean birth weight and a higher rate of meconium-stained amniotic fluid in the expectantly managed group, the overall rate of neonatal morbidity was the same as controls.

The authors concluded that "adverse pregnancy outcome in cases of isolated oligohydramnios diagnosed prior to 37 weeks appears to be related to a considerable degree of iatrogenic prematurity."

Commentary

Oligohydramnios, in general, is definitely associated with adverse outcome, mostly because it is a byproduct of conditions which, of themselves, are responsible for the adverse fallout. In IUGR, oligohydramnios results mainly from the fetus sparing his/her brain at the expense of renal plasma flow. Fetal surveillance today is so much more sophisticated with regard to the fetal circulation that an indirect assessment of amniotic fluid volume has taken on much less importance as an indicator of when to deliver a given patient. In rupture of membranes, oligohydramnios is the rule, but we use other parameters to dictate when to intervene. In renal abnormalities, such as lower urinary tract obstruction, the presence of oligohydramnios only tells us that there is an impediment to urinary flow. Oligohydramnios is simply an accompaniment to a possible problem, but certainly is not the culprit itself. When it is isolated, it is not necessarily associated with anything adverse, and may even be only a fleeting finding (as it was in 10% in the above study). This is not surprising since amniotic fluid volume varies on a day-to-day basis.

A study by Zhang et al had similar results.2 The authors focused on 113 women with isolated oligohydramnios, and found no difference in outcomes between these women and those with normal amniotic fluid volumes.

Also, oligohydramnios may be overdiagnosed depending on how it is defined. Magann et al found that in high-risk patients having biophysical profiles, the rate of oligohydramnios differed depending if AFI (38%) vs largest single vertical pocket (16%) was used.3 This translated into a 30% vs 15% rate of induction, and a cesarean section rate of 13% vs 7%, respectively, with no difference in outcomes. Based on this information, many providers have abandoned the AFI in favor of the largest single vertical pocket method.

I chose this article to discuss because of a statement made in a Society for Maternal-Fetal Medicine mini-debate, published in the same issue of the American Journal of Obstetrics and Gynecology.4 The debate focused on whether isolated oligohydramnios is reason alone to deliver patients between 34 and 37 weeks. The author, who was assigned to take the proactive stance in isolated oligohydramnios, wrote that "currently adverse outcome with expectant management is indefensible and a potential source of litigation." This warning was issued in spite of the above article in the same journal and the author's acknowledgement that "there are no current ACOG Practice Bulletins on this topic or no RCTs."

I would argue that invoking the threat of a lawsuit is not enough to justify blanket intervention in patients with isolated oligohydramnios, especially given the recently well-publicized association between late preterm birth and increased rates of cesarean section and neonatal morbidity.5 Today's nuanced forms of monitoring should allow us to identify those fetuses in this gestational age range that need to be delivered, and, just as importantly, which fetuses might benefit from being left alone.

References

  1. Melamed N, et al. Perinatal outcome in pregnancies complicated by isolated oligohydramnios before 37 weeks. Am J Obstet Gynecol 2011;205:241.e1-241.e6.
  2. Zhang J, et al. Isolated oligohydramnios is not associated with adverse perinatal outcome. BJOG 2004;111:220-225.
  3. Magann EF, et al. Biophysical profile with amniotic fluid volume assessments. Obstet Gynecol 2004;104:5-10.
  4. Chauhan SP. SMFM Debates. Oligohydramnios at 34 0/7 – 36 6/7 weeks: Observe or delivery. Am J Obstet Gynecol 2011;205:163-164.
  5. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol 2008;111:35-41.