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

Practical obstetrics info for your women's healthcare practice

What Is The ‘One-Step’ GDM Screening Approach?


There is no debate that all pregnant women should be screened for Gestational Diabetes Mellitus (GDM) between 24 and 28 weeks. However, there are two different approaches to screening for GDM. ACOG currently prefers the traditional ‘two-step’ approach, using an initial screen that, if positive, requires an additional confirmatory test. Alternatively, there is the option of the International Association of Diabetes and Pregnancy Study Groups that recommend a ‘one-step’ approach as follows

  • Perform a 75 g oral glucose tolerance test on all women, after an overnight fast, not previously found to have overt diabetes or GMD earlier in pregnancy
  • Diagnose GDM when one or more of the following plasma glucose values are exceeded
    • Fasting ≥ 92 mg/dL (5.1 mmol/l)
    • 1-hour ≥ 180 mg/dL (10.0 mmol/l)
    • 2-hour ≥ 153 mg/dL (8.5 mmol/l)
  • Early screening for overt diabetes in women at high risk for type 2 diabetes is recommended by this professional group at the first prenatal visit to allow for early detection and management for complications such as fetal anomalies and potential microvascular disease in the mother
    • If fasting plasma glucose is ≥92 mg/dL (≥5.1 mmol/l) but < 126 mg/dL (7.0 mmol/l) diagnose GDM
    • Overt diabetes as per standard cut-offs


Unfortunately, with the obesity epidemic and more sedentary lifestyles, GDM is increasing as well, and being observed in younger age groups. Complications are significant, including birth trauma to both mother and child. Treatment including diet, increased exercise and if necessary medications can be effective, if GDM is identified in time to implement these changes to achieve best results.


  • ACOG and consensus panel convened by the NIH do not recommend the ‘one-step’ approach, but rather the ‘two-step’ approach
    • Centers can adopt ‘one-step approach’ if more clinically applicable for a particular population
  • The ‘one-step’ screening approach will result in increased diagnosis of GDM
  • The controversy relates to whether with the increased costs and resources necessitated by the ‘one-step’ approach will result in improved outcomes
  • Targeting obesity and improved nutrition can also address macrosomia risks
  • The ADA recognizes ‘2 step’ Carpenter and Coustan approach or ‘1 step’ approach (see Related ObG Topics below) to both be valid for GDM diagnosis

Learn More – Primary Sources:

International Association of Diabetes and Pregnancy Study Groups Recommendations on the Diagnosis and Classification of Hyperglycemia in Pregnancy

NIDDK– Test Criteria for Prediabetes, Diabetes, and Gestational Diabetes

ACOG Practice Bulletin No. 190: Gestational Diabetes Mellitus

ADA Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes—2020