(550) Incidence of fetal growth and fluid abnormalities diagnosed by serial ultrasounds in patients with obesity

Obesity affects nearly 40% of pregnant patients.  ACOG recommends periodic growth and fluid evaluation for patients with certain comorbidities. It is unclear whether obesity, in the absence of other comorbidities, is an indication for serial ultrasound assessment. Despite this, many institutions routinely recommend serial ultrasounds for patients with obesity.  The primary objective of this study was to determine the incidence of fetal growth and fluid abnormalities in patients who underwent ultrasound assessment for the indication of maternal obesity.

Study Design:

This is a retrospective cohort study including subjects who delivered between 2019-2023 in an academic medical center where patients with obesity routinely undergo serial ultrasounds. Subjects with a singleton gestation and a pregravid (PG) body mass index (BMI) > 30.0 kg/m² were included.  Exclusion criteria included coexisting maternal, placental/umbilical cord, and fetal conditions. The results were compared by obesity class as defined by the subject’s PG BMI.

Results:

4279 subjects with obesity were screened and 1185 were included. There were 566 subjects with Class I, 351 with Class II and 268 with Class III Obesity. Demographic characteristics were similar amongst the three groups. Subjects with Class III Obesity were more likely to have an amniotic fluid abnormality (20.2%) when compared to subjects with Class I (12.3%, OR 1.82, p=0.003) and Class II Obesity (12.3% OR 1.81 p=0.008).  Mild polyhydramnios was the most common fluid abnormality amongst all groups. A growth abnormality was diagnosed in 21.9%, 27.9% and 26.9% of subjects with Class I, II and III Obesity, respectively. Suspected large for gestational age fetal weight was more common than fetal growth restriction in all groups.

Conclusion:

Among patients with uncomplicated obesity, suspected fetal growth and amniotic fluid abnormalities are common. However, when noted, these findings are often transient and resolve prior to delivery. Additional research is needed to determine the optimal frequency and timing of ultrasound assessment for patients with obesity.