Applied Evidence

Isolated oligohydramnios at term: Is induction indicated?

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Two small, randomized controlled trials (RCTs) demonstrated an increase in amniotic fluid volume in women with oligohydramnios after oral hydration.11,13 Doi demonstrated significant increases in AFI in women with oligohydramnios beyond 35 weeks when given oral hydration with free water (increase of 3.8 cm ± 1.9; P<. 001) or hypotonic intravenous solution (increase of 2.8 cm ± 1.9; P<.001) (LOE: 3).11 Interestingly, this study did not demonstrate an increase in amniotic fluid volume with intravenous hydration with isotonic fluid.

Kirkpatrick demonstrated a 30% increase in amniotic fluid compared with controls in women of unspecified gestational age with oligohydramnios given 2 liters of oral water 2 to 5 hours before repeat amniotic fluid index (LOE: 3).13

A randomized trial in women with normal amniotic fluid demonstrated a 16% increase in amniotic fluid index 4 to 6 hours after hydration with 2 liters of oral water, compared with an 8% decrease after fluid restriction during the same period.8

A recent study of daily oral hydration in women with amniotic fluid volume <10% percentile showed increased amniotic fluid volume at 1 week, suggesting long-term benefit, although the study lacked an appropriate control group (LOE: 3).33

There are no studies of clinical outcomes such as fetal heart rate decelerations during labor, or neonatal outcomes. A Cochrane systematic review concluded that maternal hydration appears to increase amniotic fluid and may be beneficial in management of oligohydramnios; however, it recommended controlled trials to assess clinical outcome benefits (LOE: 3).34

Effect of hydration on amniotic fluid index

Kilpatrick32RCTN=40, AFI 2.1–6.0; population of patients referred for antenatal testingTreatment group drank 2 L water and repeat AFI same or next dayIncrease of 1.5 ± 1.4 cm (P<.01) in treatment groupGestational ages of subjects not stated3
Kilpatrick37RCTN=40, AFI 7–24 cm, gestational 28 weeksTreatment group instructed to drink 2 L and restricted group 0.1 L water. AFI repeated in 4–6 hIncrease of 3.0 ± 2.4 cm (P<.0001) in treatment group; decrease of 1.5 ± 2.7cm in controls (P <.02)Subjects had normal AFI at entry3
Flack36Prospective cohortN=20, 10 w/AFI <5 cm, 10 controls AFI >7, 3rd trimester2 L oral water over 2 h for treatment and control groups, repeat AFI at 2 hIncrease in 3.2 cm in AFI (95% CI, 1.1–5.3) in oligohydramnios group but not in normal AFI groupImproved uterine perfusion shown by increased uterine artery velocity only in oligohydramnios group3
Doi35RCTN=84, AFI <5, at least 35 wks; randomized three maternal hydration methods (2 L oral water, hypotonic saline IV, or isotonic saline IV)Hydration with 2 L fluid and AFI repeated in 1 h compared with controlsSignificant increases in AFI in oral water and hypotonic IV groups by 3.8 cm and 2.8 cm (P<.001) respectivelyIV isotonic solutions did not increase amniotic fluid volume in study population3
RCT, randomized controlled trial; AFI, amniotic fluid index; CI, confidence interval.

Management recommendations

The AFI has low specificity and positive predictive value for oligohydramnios, and there is scant evidence that isolated term oligohydramnios causes adverse fetal outcomes. We recommend that an AFI under 5 cm should prompt additional antenatal testing rather than immediate induction in low-risk term pregnancies (SOR: B).

Though we acknowledge the lack of high-quality studies with patient-oriented outcomes to support observation and maternal hydration, we have developed a management strategy that does not require immediate induction of labor in women with uncomplicated term pregnancies.

The following recommendations apply to women having oligohydramnios as defined by amniotic fluid volume of less than 5 cm and gestational age between 37 and 41 weeks.

Initial assessment

  1. Assess for premature rupture of membranes with a thorough history and a sterile speculum exam
  2. Reassess dating as oligohydramnios in post-dates pregnancy (>41 weeks) is an indication for induction (SOR: C)35
  3. Perform a nonstress test to assess fetal wellbeing
  4. Assess for IUGR with an ultrasound for estimated fetal weight and for the ratio of head circumference (HC) to abdominal circumference (AC). A comparison with prior ultrasounds can aid in assessing interval growth. An estimated fetal weight below the 10%, an elevated HC/AC ratio, or poor interval growth would suggest IUGR
  5. Arrange for an ultrasound anatomic survey for fetal anomalies, if not done previously
  6. Determine if preeclampsia, chronic hypertension, diabetes, or other maternal conditions associated with uteroplacental insufficiency are present.

Action steps

With any positive findings in the initial evaluation, proceed to labor induction, as the patient does not have isolated, term oligohydramnios (SOR: C). If the initial assessment is unremarkable and the AFI is less than 5, consider hydration with oral water and repeating the AFI 2 to 6 hours later (SOR: B).

Persistent oligohydramnios at term, particularly with a ripe cervix, may lead you to consider labor induction. Continued expectant management of isolated term oligohydramnios with twice weekly fetal surveillance may also be a reasonable option due to the paucity of evidence that oligohydramnios is associated with an adverse outcome in this scenario (SOR: C). Normal results with umbilical artery Doppler flow studies have been used to decrease the need for induction in high-risk pregnancies with oligohydramnios, and this technique may eventually have a role in isolated term oligohydramnios.36

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