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The Preferred Timing of Second-Trimester Obstetric Sonography Based on Maternal Body Mass Index

Division of Maternal-Fetal Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland USA.

Address correspondence and reprint requests to Michael E. Lantz, MD, PO Box 3487, Salisbury, MD 21802 USA. E-mail: mlantz{at}jhmi.edu.

Objective. To determine the preferred timing of sonographic screening of fetal anatomy based on the maternal body mass index (BMI). Methods. We abstracted the sonographic reports of 2303 gravidas undergoing routine fetal anatomic screening between 15 and 24 weeks’ gestation to determine the completeness of the study. Height and weight information was available on 1444 patients. The maternal BMI (weight [kilograms]/height [square meters]) was categorized as underweight (<19.8), normal weight (19.8–26.0), overweight (26.1–29.0), and obese (>29.0). Completion rates were compared by ² analysis. Multiple logistic regression was used to evaluate for independent predictors of a completed study. Results. Except for underweight women, completion rates for all BMI categories were significantly higher when the sonographic examinations were performed between 18 weeks and 19 weeks 6 days compared with those performed between 15 weeks and 17 weeks 6 days. Body mass index, estimated gestational age, and black race were independent predictors of a completed study. Conclusions. Except in underweight women, the 18- to 20-week interval appears to be superior to the 15- to 18-week interval when performing sonographic screening of the fetal anatomy.

Key Words: estimated gestational age • fetal anatomy • maternal body mass index • prenatal sonography

Abbreviations: BMI, body mass index