Serial Third-Trimester Ultrasonography Compared With Routine Care in Uncomplicated Pregnancies: A Randomized Controlled Trial.

Objective: Among uncomplicated pregnancies, serial third-trimester ultrasound examinations identified significantly more cases with a composite of fetal growth or amniotic fluid abnormalities (27%) than did routine fundal height measurements (8%).

Methods: Women without complications between 24 0/7 and 30 6/7 weeks of gestation were randomized (NCT0270299) to either routine care (control arm) or ultrasound examination every 4 weeks (intervention arm). The primary outcome was a composite of abnormalities of fluid volume and growth: oligohydramnios or polyhydramnios; fetal growth restriction; or large for gestational age. The secondary outcome was the presence of composite maternal or neonatal morbidity among the two groups. A total of 206 participants was needed to have 80% power to detect an increase in the primary composite outcome from 10% in control to 25% in the intervention group (baseline rate 10%; two-tailed; α=0.05; loss to follow-up 5%). All women were included in the intent-to-treat analysis. Fisher exact, χ tests, or two-sample t tests were used to assess group differences.

Results: From July 11, 2016, to May 24, 2017, 852 women were screened for eligibility and 206 were randomized as follows: 102 in routine care and 104 in serial ultrasound examinations. The two groups were comparable in baseline characteristics. The primary composite outcome was significantly higher among women who were in the ultrasound examination group than the routine care group (27% vs 8%; relative risk 3.43, 95% CI 1.64-7.17); five women (95% CI 3-11) were needed to identify at least one of the composite ultrasound abnormalities. Although we were underpowered to detect a significant difference, the following secondary endpoints occurred with similar frequency in the ultrasound examination group than the routine care group: induction resulting from abnormal ultrasound examination findings (14% vs 6%), cesarean delivery in labor (5% vs 6%), and prespecified composite maternal morbidity (9% in both groups) and composite neonatal morbidity (1% vs 4%).

Conclusion: Among uncomplicated pregnancies between 24 0/7 and 30 6/7 weeks of gestation, serial third-trimester ultrasound examinations were significantly more likely to identify abnormalities of fetal growth or amniotic fluid than measurements of fundal height and indicated ultrasound examination. No differences in maternal and neonatal outcomes were noted, although we were underpowered for these endpoints.

Clinical Trial Registration: ClinicalTrials.gov, NCT02702999.