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

J Ultrasound Med. 2020 Nov;39(11):2123-2130. doi: 10.1002/jum.15319. Epub 2020 May 8.


Objectives: 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 180/7 to 196/7 weeks.

Methods: 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 , 180/7 to 196/7 weeks; 25 to 29.9 kg/m2 , 190/7 to 206/7 weeks; 30 to 34.9 kg/m2 , 200/7 to 216/7 weeks; 35 to 39.9 kg/m2 , 210/7 to 226/7 weeks; and 40 kg/m2 or higher, 220/7 to 236/7 weeks. In period A, assessments were scheduled between 180/7 and 196/7 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.

Results: 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).

Conclusions: In pregnancies with obesity, a protocol delaying the initial assessment beyond 196/7 weeks based on the maternal BMI does not reduce the rate of inadequate visualization.

Keywords: body mass index; fetal anatomy; obesity; prenatal diagnosis; ultrasound.

MeSH terms

  • Body Mass Index
  • Female
  • Humans
  • Logistic Models
  • Obesity*
  • Pregnancy
  • Retrospective Studies
  • Ultrasonography, Prenatal*