Limitations of the fetal anatomic survey via ultrasound in the obese obstetrical population.

Objective: To evaluate limitations of the fetal anatomic survey in obese women.

Methods: Retrospective cohort study of obese gravidas with singleton gestations who had at least one, sonographic fetal evaluation at ≥ 14 weeks between January 2009 and March 2011. The impact of pre-pregnancy body mass index (BMI), placental location, prior cesarean scar and sonographer experience on ability to achieve an adequate ultrasound was evaluated using multilevel modeling. Ability to visualize specific fetal parts by BMI class and gestational age was also evaluated.

Results: There were 245 obese women (42% with class III obesity). Senior faculty (>20 years experience) were more likely to achieve adequate visualization (adjusted odds ratio [aOR] 3.27; 95% confidence interval [CI] 1.15-9.25) compared with junior faculty. Among women with BMI > 40.0, odds of inadequate views of the face and spine were 10.0 (95% CI 1.31-76.0) and 5.17 (95% CI 0.65-40.8), when compared with women with a BMI = 30-34.9. Odds for inadequate views of sex (OR 3.83; 95% CI 0.86-17.1) and extremities (OR 4.37; 95% CI 0.99-19.4) were similarly increased with a BMI ≥ 40. The optimal gestational age for a complete anatomic survey was 22-24 weeks (93% completion rate), with an OR of 41.3 (95% CI 7.89-215.8), compared with a survey at 14-16 weeks.

Conclusions: Attending sonographer experience is associated with improved visualization of fetal anatomy among obese gravidas. Face, spine, sex and extremity views are particularly difficult in the highest BMI category.