Abnormal amniotic fluid volume as a screening test prior to targeted ultrasound

The purpose of this study was to examine (1) the association between amniotic fluid volume (AFV) and sonographically detected fetal structural anomalies, and (2) the effectiveness of using abnormal AFV as a screening test prior to patient referral for a targeted ultrasound.

For singleton pregnancies in the 2nd and 3rd trimester frequencies of individual anomalies and odds ratios were calculated for each category of amniotic fluid volume relative to the frequency of anomalies with normal volume. The anomaly detection rate and frequency of referral for targeted ultrasound on the basis of abnormal amniotic fluid volume were calculated.

15,959 (92.0%) of patients had normal amniotic fluid volume, 537 (3.1%) decreased, 544 (3.1%) increased, 167 (1.0%) oligohydramnios, and 141 (0.8%) polyhydramnios. There were 365 (2.1%) fetuses with major structural anomalies. 1.8% of patients with normal AFV had anomalies. Anomalies were significantly more frequent in all categories of abnormal fluid: decreased (3.2%, OR 1.74, 95% CI 1.06-2.86), increased (5.7%, OR 3.22, 95% CI 2.2-4.71), oligohydramnios (9.0%, OR 5.26, 95% CI 3.09-9.05), and polyhydramnios (5.7%, OR 3.21, 95% CI 1.56-6.6). Referral for targeted ultrasound based on any abnormal AFV volume compared to only oligohydramnios or polyhydramnios increased the overall anomaly detection rate by nearly three-fold (19.5% vs. 6.3%), with minimal changes in the number of referrals per anomaly detected (13.4 vs.

Referral for targeted ultrasound in the presence of even minor abnormalities of amniotic fluid would significantly improve anomaly detection with minimal increase in referrals.