Delay of Fetal Anatomy Ultrasound Assessment Based on Maternal Body Mass Index Does Not Reduce the Rate of Inadequate...

To determine whether delay of initial anatomy ultrasound based on the maternal body mass index (BMI) reduces the rate of inadequate visualization compared to standard timing at 18^0/7 to 19^6/7 weeks.

A retrospective study of singleton anatomy assessments was conducted at a tertiary care center in the 2-year period before (A, 2012-2014) and after (B, 2014-2016) protocol initiation. Assessments in period B were scheduled on the basis of the BMI in the first trimester: lower than 25 kg/m² , 18^0/7 to 19^6/7 weeks; 25 to 29.9 kg/m² , 19^0/7 to 20^6/7 weeks; 30 to 34.9 kg/m² , 20^0/7 to 21^6/7 weeks; 35 to 39.9 kg/m² , 21^0/7 to 22^6/7 weeks; and 40 kg/m² or higher, 22^0/7 to 23^6/7 weeks. In period A, assessments were scheduled between 18^0/7 and 19^6/7 weeks. The rate of inadequate visualization and repeated assessments in periods A and B were compared. Multivariable logistic regression, per-protocol, and BMI subgroup analyses were completed.

In total, 3491 pregnancies in period A and 3672 in period B were included. In period B, 74% were scheduled per protocol; however, this rate decreased for higher-BMI categories (52% for BMI ≥40 kg/m² ). The inadequate visualization rate was slightly higher in period B versus A (16.9% versus 15.0%; P = .03) and exceeded 35% for a BMI of 40 kg/m² or higher, with or without delay. After adjusting for maternal age and fetal presentation, period B had small increased odds of inadequate visualization versus period A (adjusted odds ratio, 1.2; 95% confidence interval, 1.02-1.38). Repeated assessment rates were similar in periods B and A (14.0% versus 13.1%; P = .25).

In pregnancies with obesity, a protocol delaying the initial assessment beyond 19^6/7 weeks based on the maternal BMI does not reduce the rate of inadequate visualization.