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Obesity in Pregnancy: Classification and Clinical Implications


The prevalence of obesity in women of reproductive age (20 to 39) in the US is 39.7%. Prevalence is found to be lowest among non-Hispanic Asian women (17.2%) and higher in non-Hispanic White (39.8%), Hispanic (43.7%), and non-Hispanic black (56.9%) women (2017 to 2018 data). Obesity is commonly classified based on body mass index (BMI). BMI is defined as weight in kg divided by height in meters squared (kg/m2). Definitions are as follows

  • Underweight: BMI <18.5
  • Normal weight: BMI 18.5 to 24.9
  • Overweight:  BMI 25 to 29.9
  • Obesity class I: BMI 30 to 34.9
  • Obesity class II: BMI 35 to 39.9
  • Obesity class III: BMI ≥40


Potential Fetal and Maternal Complications

Antepartum effects

  • Increased risk of spontaneous abortion and recurrent miscarriage
  • Increased risk of stillbirth
  • Increased risk of fetal anomalies include:
    • Neural tube defects
    • Cardiovascular abnormalities
    • Cleft lip and palate
    • Anorectal atresia
    • Hydrocephalus
    • Limb reduction anomalies
  • Increased risk of maternal cardiac dysfunction, proteinuria, sleep apnea, fatty liver disease, gestational diabetes , preeclampsia

Intrapartum effects

  • Increased risk of
    • Cesarean sections
    • Failed trial of labor
    • Endometritis
    • Wound dehiscence
    • Deep venous thrombosis

Post-partum effects

  • Weight retention
  • Metabolic dysfunction
  • Pregravid obesity in future pregnancies
  • Early termination of breast feeding
  • Post-partum anemia
  • Depression

Fetal and childhood risks

  • Increased risk of neonatal and infant death
  • Macrosomia
  • Impaired growth
  • Metabolic syndrome
  • Childhood obesity

Management Considerations

Preconception Care

  • Behavioral interventions
    • Focus on diet and exercise to improve outcomes vs exercise alone
    • Encourage weight loss prior to pregnancy
  • Refer to behavioral counseling with interventions focused on nutrition, diet and exercise

Note: USPSTF recommends clinicians offer behavioral counseling interventions to promote healthy weight gain and preventing excess gestational weight gain in pregnancy to all pregnant women (see ‘Learn More – Primary Sources’ below) | Table 2 includes a comprehensive summary of behavioral counseling interventions

Prenatal Care

  • Calculate BMI to guide diet and exercise counseling at initial visit
  • Counsel patients about limitations of identifying structural anomalies with ultrasound in obese patients
  • Glucose intolerance
    • Assess for glucose intolerance risk factors including
      • ≥BMI 30 | Previous GDM | Impaired glucose metabolism
    • Recommend early glucose screening for those with risk factors (list for early screening factors can be found in ‘Related ObG Topics’ by tapping on ‘Updated ACOG Guidance on Gestational Diabetes’)
  • Weekly antenatal fetal surveillance
    • BMI of 35 to 39.9: Consider initiating weekly surveillance at 37w0d
    • BMI ≥40 or greater: Consider initiating weekly surveillance at 34w0d

Intrapartum Care

  • Labor pattern
    • First stage of labor may be prolonged in obese patients
    • Consider delaying cesarean delivery for labor arrest
  • Cesarean incision
    • Optimal skin incision is unclear
    • Vertical may be associated with increased complications
    • Supraumbilical incision may be helpful in the presence of a large panniculus
  • Prophylactic antibiotics prior to cesarean
    • Weight-based dosing may be considered
      • BMI ≥30 or weight ≥80 kg: 2 g cefazolin
    • Postoperative oral regimen in obese individuals who may not have received IV azithromycin
      • 500-mg oral cephalexin and 500-mg metronidazole every 8 hours for 48 hours
  • Skin cleansing prior to cesarean
    • Use an alcohol-based solution such as chlorhexidine–alcohol
  • Vaginal cleansing
    • Prior to both vaginal or cesarean delivery with either povidone–iodine or chlorhexidine gluconate

Postpartum Care

  • VTE mechanical prophylaxis
    • Recommended prior to and after cesarean delivery
    • CMQCC recommends mechanical prophylaxis for BMI >40 for vaginal birth
  • VTE chemoprophylaxis
    • LMW heparin: Enoxaparin 40 mg daily commonly used as prophylactic dose following surgery
    • Weight-based VTE chemoprophylaxis dosing may be considered in Class III obesity following cesarean
      • 0.5 mg/kg enoxaparin every 12 hours starting 12 hours after surgery (based on prospective cohort study)
    • Subcutaneous drains
      • Do not use routinely after cesarean due to increased risk for wound complications

Learn More – Primary Sources:

ACOG Practice Bulletin 230: Obesity in Pregnancy

ACOG Committee Opinion No. 548 :Weight Gain During Pregnancy

USPSTF: Behavioral Counseling Interventions for Healthy Weight and Weight Gain in Pregnancy