(644) Indicated versus universal third trimester ultrasound examination in low-risk pregnancies: a pre- and post-intervention trial

In low-risk pregnancies, third trimester ultrasound examination (USE) are indicated if there is discordance between fundal height vs. gestational age. The primary objective was to compare the composite neonatal adverse outcomes (CNAO) with routine care vs. universal third trimester USE in low-risk pregnancies. The secondary objective was to compare the composite maternal adverse outcomes (CMAO).

Study Design:

Our multi-site quality improvement trial included low-risk women, defined as without medical or fetal indications for USE in the third trimester. Compared to routine care in pre-implementation, in the post-implementation period all patients were scheduled for USE at 36-37 weeks. Clinicians intervened based on abnormalities identified with these USE. CNAO was a composite of Apgar score < 5 at 5 min, birth trauma, intubation for >24 hours, seizure, sepsis, meconium aspiration syndrome, IVH, PVL, NEC, or death. CMAO included chorioamnionitis, wound infection, PPH, blood transfusion, DVT, ICU admission, or death. We used Bayesian statistics to estimate a sample size of 600 individuals in each arm to detect >75% probability of any risk reduction in CNAO, (80% power; 50% risk reduction with USE). Posterior probability of risk reduction, posterior median relative risk (pRR) with 95% credible intervals (CrI), and number needed to treat (NNT) were calculated.

Results:

The primary outcome occurred in 15 of 568 (2.6%) individuals in the pre- and 12 of 661 (1.8%) in the post-intervention group, with an 83% posterior probability of risk reduction in CNAO (pRR 0.69, 95% CrI 0.34-1.42). CMAO occurred in 8.6% in the pre- and 6.5% in post-intervention group, with a 90% posterior probability of risk reduction in CMAO (pRR of 0.74, 95% CrI 0.49-1.15). The NNT to reduce CNAO was 121, to reduce CMAO was 46, and to reduce primary CD was 43 (Table).

Conclusion:

Among low-risk pregnancies, compared to routine care with indicated USE, implementation of a universal third-trimester USE at 36-37 weeks was associated with an improvement in composite neonatal and maternal adverse outcomes.