Obesity and Pregnancy

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Definition and Epidemiology

  • Obesity - classified by BMI 

    • Prevalence of obesity has increased to 34.0% in women 20-39 years in 2010  

ACOG PB 230

Effect of Obesity on Pregnancy 

  • Pregnancy Loss 

    • Increased risk of SAB (1.2 OR) and recurrent miscarriage (OR 3.5) 

    • Also have increased risk of pregnancies affected by neural tube defects, hydrocephaly, and other anomalies 

  • Pregnancy Complications 

    • Antepartum

      • Medical issues: increased risk of cardiac dysfunction, proteinuria, sleep apnea, nonalcoholic fatty liver disease 

      • Pregnancy issues: increased risk of gestational diabetes, preeclampsia, stillbirth 

        • Risk of stillbirth increases with increasing obesity

          • OR 1.71 for BMI 30-34.9

          • OR 2.0 for BMI 35.0-39.9

          • OR 2.48 for BMI >40

          • OR 3.16 for BMI > 50

        • Of note, the practice bulletin does point out that black pregnant people with obesity have a higher risk of stillbirth than white pregnant people - discusses that while this is not a biological reason, is a proxy for likely negative influence of racism on health 

    • Intrapartum

      • Increased risk of cesarean delivery, failed trial of labor, endometritis, wound rupture/dehiscence, and venous thrombosis  

      • Decreased likelihood of VBAC after TOLAC 

    • Postpartum Complications - increased risk of future metabolic dysfunction 

    • Fetal complications - increased risk of growth abnormalities 


  • How Can We Manage Obesity Before And During Pregnancy 

  • Pre-pregnancy Counseling 

    • Discussion of control of obesity with weight loss (either surgical or non-surgical) 

    • Even small weight loss can be associated with improved outcomes (even 5-10%) 

    • Can try motivational interviewing 

      • Encourage diet, exercise, and behavior modification 

    • Medications 

      • Not recommended pre-pregnancy or during pregnancy 

  • During Pregnancy 

    • Recommended weight gain 

      • Overweight: recommend 15-25 lb weight gain 

      • Obese: recommend 11-20 lb weight gain 

      • There is a lack of data regarding short-term and long-term maternal and newborn outcomes, no recommendation for lower targets for pregnant women with more severe degrees of obesity 

    • Congenital Anomalies

      • As previously discussed, increased risk of congenital anomalies, but detection of these anomalies is significantly decreased with increasing maternal BMI 

      • Cell-free DNA test failures are also more frequent in patients that are obese. This is because a minimum fetal fraction of 2-4% usually is needed. The median fetal fraction between 10-14 weeks is around 10%, but with increasing BMI, it’s associated with decreased fetal fraction. 

      • Can consider repeating screening if it’s because of early gestation, but not recommended if there are ultrasound findings of anomalies 

    • Metabolic Disorders - screen for glucose intolerance and OSA at first antenatal visit with history, exam, and labs 

      • Sleep medicine evaluation 

      • Can consider early glucose screening; if negative, repeat at usual time of 24-28 weeks 

    • Stillbirth and Antepartum fetal testing 

      • This is going to be different based on your institution 

      • Can consider weekly testing after 37 weeks for BMI 35-39.9 

      • Can consider weekly testing after 34 weeks for BMI >40 

  • Intrapartum 

    • Many studies that show an increased risk of C-section among overweight and obese women 

      • There are studies that show an increased length of time in labor; another study showed that maternal BMI was not associated with longer second stage 

      • Maybe consider allowing more time in first stage of labor before C-section in obese individuals? 

      • Remember that pregnant women with higher BMI have a higher rate of complications with elective repeat cesarean section - so not a reason to not TOLAC them! 

    • Some considerations during labor 

      • Consider anesthesia consult - especially if OSA. An epidural may be technically more difficult to place 

      • Antibiotics - may need to increase the amount of Ancef before C-section (remember usual is 2g). Increase to 3g if >120 kg 

  • Postpartum 

    • There is an increased risk of VTE in obese women, so definitely use your SCDs and encourage early mobilization  

    • In very high risk groups, discuss pharmacologic thromboprophylaxis 

      • Dose can be BMI stratified

        • BMI < 40: 40 mg Lovenox daily 

        • If BMI 40-59.9: 40 mg BID 

        • If BMI 60 or greater: 60 mg BID