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Do obese women without comorbid conditions need a growth ultrasound during pregnancy?

      Objective

      It is common to perform growth ultrasounds for women with obesity. This poses a dilemma for busy units due to increasing prevalence, sonographers injury, and increased time of examinations. Our hypothesis is that additional growth ultrasounds are not necessary for women with obesity to predict fetal growth restriction (FGR) or small for gestational age (SGA) infants.

      Study Design

      We performed a retrospect chart review of 7,620 anatomy (76805) and targeted (76811) exams. Data was paired with corresponding 28 and 32 week growth evaluations and birth weight percentile using the Fenton 2013 newborn chart. We compared baseline characteristics using chi2, Fischer’s exact as indicated. Chi2 and logistic regression controlling for confounders was performed for each gestational age and birthweight.

      Results

      Women with a prepregnancy BMI ≥30 were less likely to experience FGR at 28 weeks (OR 0.43 95%CI 0.27-0.68 p=0.0), 32 weeks (OR 0.54 95%CI 0.36-0.81 p= 0.0), and SGA (OR 0.50 95% CI 0.33-0.77 p=0.0). There was a significant difference in maternal age between groups (the FGR group found to be on average 2.5 years younger) but no difference in confounders such as chronic hypertension, pregestational diabetes, or race. Logistic regression controlling for maternal age demonstrated women with a prepregnancy BMI ≥30 were significantly less likely to have FGR at 28 weeks (aOR0.40 95%CI 0.26-0.62 p=0.0) or 32 weeks (aOR 0.51 95%CI 0.34-0.76 p=0.0) or SGA (aOR 0.50 95%CI 0.33-0.75).
      A secondary analysis by class of obesity did not show significant differences aside from Class 3 obesity (BMI ≥40) which was associated with decreased FGR at 28 and 32 weeks (aOR 0.32 95%CI 0.16-0.57 p=0.0) and SGA (aOR 0.30 CI 0.13 - 0.61 p=0.0). This effect remained significant when controlling for diabetes and chronic hypertension given increased risk.

      Conclusion

      Our review showed that, in our patient population, prepregnancy obesity was associated with lower rates of SGA and FGR. This calls into question the routine practice of performing repeated growth ultrasounds in patients with obesity but no additional risk factors for FGR.
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