Applied Evidence

Isolated oligohydramnios at term: Is induction indicated?

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References

No studies have directly addressed whether labor induction improves outcomes. A meta-analysis of 18 studies examining outcomes of pregnancies with AFI <5 cm found an increased risk of cesarean delivery for fetal distress and low Apgar scores at 5 minutes. Most of these studies, however, had high-risk patients including IUGR (level of evidence [LOE]: 2).21

A recent study of high-risk patients failed to detect a difference in the incidence of nonreactive nonstress tests, meconium-stained amniotic fluid cesarean delivery for fetal distress, low Apgar scores, or infants with a cord pH of <7.10 when oligohydramnios (AFI <5.0 cm) was present (LOE: 1).2 The patients with oligohydramnios were all induced, while many of the other high-risk patients were expectantly managed. The study therefore provides no guidance on the safety of expectant management for patients with oligohydramnios. To eliminate the potential effect of induction versus expectant management the same authors performed a case-control study of 79 high-risk women with AFI <5 cm matched to 79 women with the same high-risk pregnancy complication who had an AFI >5 cm at the time of induction (LOE: 2).23 They failed to detect any significant differences in neonatal outcomes between the groups.

Studies of the “borderline” AFI (between 5 cm and 8 cm) may also demonstrate an association with adverse neonatal outcomes if researchers include fetuses with IUGR or malformations. In one retrospective case review of 214 women with AFI of 5 cm to 10 cm, the only statistically significant finding was an association with IUGR.3 The authors recommended antepartum surveillance twice a week for mothers with borderline AFI, but they did not comment on induction (LOE: 2). Correspondence regarding this study argued that this recommendation was not supported by the evidence and would lead to unnecessary antenatal testing.24

Studies of isolated oligohydramnios

Investigators have conducted studies (Table 1) excluding fetuses with intrauterine growth restriction or anomalies to try to determine if isolated oligohydramnios is associated with poorer outcomes.25-30

Rainford’s study of outcomes in exclusively term, low-risk patients failed to show significant outcome differences in Apgar scores, NICU admissions, or rates of cesarean delivery for non-reassuring fetal heart rate monitoring (LOE: 2).29 This study was limited due to its retrospective design. The authors comment that the relatively good outcomes in the oligohydramnios group may be due to the widespread practice of inducing such patients.

In a case-control study by Conway, 183 low-risk, term parturients with oligohydramnios were matched to 183 women of similar gestational age and parity who presented in spontaneous labor. The patients with isolated oligohydramnios were induced and showed an increased cesarean delivery rate. The increased rate of cesarean delivery was not due to nonreassuring fetal surveillance and was attributed to the induction process (LOE: 2).25

An analysis of woman diagnosed with isolated oligohydramnios (AFI <5) at any gestational age in the multicenter prospective RADIUS trial demonstrated similar perinatal outcomes and fetal growth compared with pregnancies with a normal amniotic fluid (LOE: 2).30

The only randomized clinical trial of labor induction vs expectant management for term isolated oligohydramnios showed similar outcomes in each group. But this study was small (n=61) and has only been published as an abstract.31

TABLE 1
Isolated oligohydramnios and perinatal outcomes

StudyDesignStudy number n vs controlsPatient-oriented outcomesCommentLOE
PopulationSignificant findingsNon-significant findings
Garmel19Prospective cohortN=187Increased preterm birth (OR=3.23; 95% CI, 1.4–7.3) in oligohydramnios groupIUGR, asphyxia, death, NICU admitDelivery recommended at 37 weeks2
17–37 week with subnormal EFW (>10%)65 AFI <8 cm vs 122 AFI >8 cm
Conway18Prospective cohortN=366Increased CS rate (OR=2.7 95% CI, 1.3–5.4) in oligohydramnios groupCS for fetal distress; all neonatal outcomesTreatment group induced, controls spontaneous2
Term, isolated oligohydramnios undergoing induction183 AFI <5 cm vs 183 AFI >5 cm
Roberts21Prospective cohortN=206Increased IUGR (OR=5.2; 95% CI, 1.6–22), induction (OR=34.4, 95% CI, 4–1425.5), NICU admit (OR=9.8; 95% CI, 1.3–432)Fetal distress requiring CSUsed >5%ile to exclude IUGR. Included some high-risk pts (diabetes or hypertension)2
3rd trimester, isolated oligohydramnios103 AFI 3%ile (N=103) vs matched control
Rainford22Retrospective cohortN=232Induction rate for AFI <5 = 98% vs 51% AFI >5 P<.001; increased meconium staining in controls without oligohydramniosNICU 2 admissions, 5-minute Apgar scores 2
37–41 week, low-risk. AFI within 4 days of deliveryAFI <5 (n=44) vs >5 (n=188)
Zhang23Retrospective nested cohortN=6657Malpresentation (RR=3.5, 95% CI 1.8–6.60)Fetal growth, CS, low Apgar, overall neonatal morbidityBenefit of routine ultrasound was the primary study outcome study endpoint2
Term or near-term, low-riskAFI <5 (n=86) vs >5 (n=6571)
AFI, amniotic fluid index; CI, confidence interval; CS, cesarean section; EFW, estimated fetal weight; IUGR, intrauterine growth restriction; LOE, level of evidence; NICU, neonatal intensive care unit; OR, odds ratio; RR, relative risk.

Effect of maternal hydration

Maternal hydration status and plasma osmolality have an affect on amniotic fluid volume (Table 2). Maternal hydration with oral water or intravenous hypotonic solutions has been shown to increase amniotic fluid volume.8,11-13 Oral hydration with hypotonic fluid has been demonstrated to increase fetal urine production in one observational study.32 Another observational study demonstrated increased amniotic fluid volume and uteroplacental perfusion without alteration of fetal urine production suggesting the possibility that transmembranous fluid shifts from the placenta to the amniotic cavity may be involved.12

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