Effect of increased body mass index on first-trimester ultrasound examination for aneuploidy risk assessment

OBJECTIVE: To estimate whether body mass index (BMI) affects the evaluation of nuchal translucency or the nasal bone during first-trimester ultrasound examination for aneuploidy risk assessment. METHODS:: Six hundred ninety-four women with singleton gestations undergoing first-trimester aneuploidy risk-assessment ultrasound examinations were identified. Weight categories were defined as normal (body mass index [BMI] less than 25), overweight (25-29.9), and obese (at or above 30). χ², χ² for trend, Student t test, one-way analysis of variance, and Pearson correlation were used for statistical analysis where appropriate to estimate the effect of BMI on first-trimester ultrasound examination. P<.05 was considered statistically significant. RESULTS:: Increasing BMI was significantly associated with an inadequate nasal-bone assessment (3% compared with 12.7%, P<.001), increased ultrasound examination time (15.23±8.09 minutes compared with 17.01±7.97 minutes, P=.028), and an increased need to perform a transvaginal ultrasound examination (23% compared with 41.8%, P<.001). Prior abdominal surgery was not significantly associated with nasal-bone assessment inadequacy (7.8% compared with 4.4%, P=.125), the need to perform transvaginal ultrasound examination (33.6% compared with 28.6%, P=.279), or longer examination time (16.22±8.6 minutes compared with 15.92±7.8 minutes, P=.704). CONCLUSION:: In singleton pregnancies, increased BMI is not associated with suboptimal visualization of nuchal translucency, but it is associated with a longer time to perform the first-trimester ultrasound examination for aneuploidy risk assessment, increased need for transvaginal ultrasound examination for nuchal-translucency visualization, and a lower likelihood of obtaining an adequate nasal-bone image. Previous abdominal surgery did not affect the ability to visualize the nasal bone.