Third trimester ultrasound accuracy and delivery outcome in obese and morbid obese pregnant women

Objective: Several studies have highlighted the negative impact of maternal obesity on ultrasound accuracy for fetal weight estimation (EFW). However, the evidence is conflicting. We aimed in our study to find if the ultrasound accuracy for EFW would differ or decrease in obese and morbid obesity classes. We also studied the mode of delivery within the same cohort.

Methods: It is a retrospective study of obese patients with recorded BMI ≥30?kg/m², class I and II (BMI: 30–39.9?kg/m²) compared with extreme obese class III (BMI ≥40?kg/m²), who gave birth after 28-week gestation of viable singleton, who had an ultrasound within 7 d of delivery with reported normal amniotic fluid and no major fetal anomaly; the EFW was consistently measured through Hadlock regression formula in the period of 2014–2015 inclusive. Differences between the EFW and actual birth weight (ABW) were assessed by percentage error, accuracy in predictions within ±10% of error and the Pearson correlation coefficient were used to correlate EFW with the ABW. The study’s secondary outcome was to study the mode of delivery and the rate of cesarean section in obese and morbid obese patients.

Results: Total 106 cases fulfilled our criteria. Class I and II as the first group (n?=?53). Class III as the second group (n?=?53). Maternal and birth characteristics were similar. The Pearson correlation coefficient equal 1 in both groups. The overall mean absolute difference (MAD) in grams of the whole obese cohort was 242?±?213. The MAD was 242?±?202 and 242?±?226?g for the first and second group, respectively (p?=?1.0). The overall mean absolute percentage error (MAPE) in this obese cohort was 8%. The MAPE for the first and second group, respectively were 8 and 7% (p?=?0.4). The overall rate of cesarean delivery was 60% (64/106) with no differences between the obese and morbid obese BMI classes. Sixty-six percentage (42/64) of these cesarean cases was for repeat cesarean section.

Conclusion: Despite what has been previously reported about the negative impact of maternal obesity on EFW accuracy, we could not demonstrate this relationship in our obese cohort (MAPE <10%). In addition, we could not illustrate a significant difference in ultrasound accuracy across various obesity classes. However, we found a significantly increased rate of delivery by repeated cesarean section in this obese cohort.