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Is Previous Bariatric Surgery Linked to Smaller Fetal Size and Birthweight?


  • While bariatric surgery has benefits, including an association with improved pregnancy outcomes, there have also been reports of greater prevalence of small babies
  • Maric et al. (BJOG, 2020) investigated the intrauterine fetal growth pattern and fetoplacental circulation in pregnancies following bariatric surgery


  • Prospective study
  • Participants
    • Pregnant women
    • Similar BMIs, with and without history of bariatric surgery
  • Study design
    • An oral glucose tolerance test (OGTT) was performed at 27 to 30 weeks
    • At three time-points (20 to 24w; 30 to 33w; 35 to 37w) in pregnancy, the following fetal biometric measurements were measured
      • AC
      • FL
      • EFW
      • Fetoplacental Dopplers
    • Birthweight (BW) was recorded
    • Variables were modelled after adjustment for maternal/pregnancy characteristics
      • Model estimates are reported as posterior means and quantile-based 90% credible intervals (CrI)
  • Primary outcome measurements
    • Fetal biometry
    • Fetoplacental Doppler
    • BW


  • 162 women included | No difference in mode of delivery
    • Bariatric surgery: 54
    • Control: 108
  • Compared with the no surgery control group, the bariatric surgery group had lower EFW, smaller AC and FL with differences increasing from earlier to later gestational time points
    • EFW at 35 to 37 weeks: Difference −120 g (90% Crl, −189 g to −51 g) lighter
    • AC at 35 to 37 weeks: Difference -6.1 mm (90% Crl, -10.0 to -2.1)
    • FL at 35 to 37 weeks: Difference -0.9 mm (90% Crl, -1.6 to -0.3)
    • No difference in HC
  • Infants born to mothers in the bariatric surgery group were lighter
    • −202 g (90% Crl, −330 g to −72 g)
    • Adjusted for maternal age, parity, smoking status, first trimester BMI, GDM status and and gestational age at delivery
  • There was no difference in the fetoplacental Doppler indices between groups
  • Maternal glucose levels
    • Were positively correlated with third-trimester EFW and BW
    • Fasting and 2 hour glucose levels were lower in the post‐bariatric vs no surgery group


  • Offspring of women who had previous bariatric surgery were smaller both during pregnancy and after birth vs women with comparable BMI who had no surgery
  • The authors suggest that the size difference may be related to lower maternal glucose levels in the bariatric surgery group
  • Fetoplacental circulation does not appear to be altered by maternal bariatric surgery

Learn More – Primary Sources:

Fetal growth and fetoplacental circulation in pregnancies following bariatric surgery: a prospective study