What weight gain should a pregnant woman aim for in each trimester based on her pre‑pregnancy body mass index (BMI)?

Weight Gain Recommendations by Trimester Based on Pre-Pregnancy BMI

Pregnant women should gain 1.4-2.3 kg during the first trimester regardless of BMI category, then follow BMI-specific weekly rates of 0.5-0.9 kg/week (normal weight), less than 0.5 kg/week (overweight), or approximately 0.4 kg/week (obese) during the second and third trimesters to achieve total gains of 12.5-18 kg (underweight), 11.5-16 kg (normal), 7-11.5 kg (overweight), or 5-9 kg (obese). 1

First Trimester Weight Gain (Weeks 0-13)

• All BMI categories should gain 1.4-2.3 kg during the first trimester, with steady and progressive gain throughout this period 2, 1
• Energy needs do not increase during the first trimester unless the woman begins pregnancy with depleted body reserves 2, 1
• Gaining more than 2.3 kg in the first trimester for normal-weight women signals potential excessive total weight gain and requires immediate counseling 3

Second and Third Trimester Weight Gain (Weeks 14-40)

Underweight Women (BMI <18.5 kg/m²)

• Total pregnancy goal: 12.5-18 kg (28-40 lbs) 1
• After the initial 1.4-2.3 kg in first trimester, aim for the higher end of the 0.5-0.9 kg/week range during second and third trimesters 1
• These women require greater total weight gain to reduce risk of small-for-gestational-age infants and preterm birth 1, 4

Normal Weight Women (BMI 18.5-24.9 kg/m²)

• Total pregnancy goal: 11.5-16 kg (25-35 lbs) 1
• Rate during second and third trimesters: 0.5-0.9 kg per week 2, 1
• This represents the standard reference range from which other categories are adjusted 1
• Women gaining more than 0.9 kg per week after the first trimester are at increased risk of excessive weight gain 3

Overweight Women (BMI 25-29.9 kg/m²)

• Total pregnancy goal: 7-11.5 kg (15-25 lbs) 1
• Rate during second and third trimesters: less than 50% of normal-weight rates (approximately 0.25-0.45 kg per week) 2, 1
• Should not exceed 11.5 kg total to minimize risks of gestational hypertension, pre-eclampsia, and large-for-gestational-age infants 3

Obese Women (BMI ≥30 kg/m²)

• Total pregnancy goal: 5-9 kg (11-20 lbs), with approximately 7 kg recommended 2, 1
• Rate during second and third trimesters: approximately 0.4 kg per week or less 1
• Should not exceed 9 kg total to reduce substantial risks of gestational diabetes, cesarean delivery, and macrosomia 3
• May require fewer than 300 additional kcal/day due to ample body fat stores 2

Nutritional Requirements to Support Appropriate Gain

• No additional calories needed in first trimester unless depleted body reserves are present 2, 1
• Add 300 kcal/day during second and third trimesters only for normal-weight women 2, 1
• Obese women may require only 100 kcal/day additional during second and third trimesters while still achieving successful pregnancy outcomes 2
• Protein intake: 0.75 g/kg/day plus an additional 10 g/day throughout pregnancy 2, 1
• Iron supplementation: 30 mg/day during second and third trimesters 2, 1
• Folic acid: 400 µg/day from fortified foods and/or supplements 2, 1

Critical Clinical Considerations

Monitoring and Early Intervention

• Establish baseline weight at the first prenatal visit to calculate pre-pregnancy BMI accurately 5, 3
• Implement regular weight checks at each prenatal visit with documentation of cumulative gain 5
• Discuss weight gain expectations early in pregnancy, as many women report not being aware of guidelines 2, 5

Risk Stratification

• Pre-pregnancy overweight or obesity is the strongest predictor of excessive gestational weight gain 1, 3
• Younger maternal age (adolescents and young women) is associated with higher weight gain 1, 3
• Multigravid women with high BMI may gain less weight (3.3 kg) compared to primigravid high BMI women (6.9 kg) 6

Consequences of Inappropriate Gain

• Excessive gain increases risks of: gestational hypertension, pre-eclampsia, gestational diabetes, large-for-gestational-age infants, cesarean delivery, and long-term maternal weight retention 1, 5, 3
• Inadequate gain (affecting 20% of women) increases risks of: preterm birth and small-for-gestational-age infants 1, 5
• Approximately 37% of pregnant women gain more than recommended, while only one-third gain within guidelines 3, 7

Common Pitfalls to Avoid

• Failing to provide specific BMI-based targets early in pregnancy leads to women relying on inaccurate information from family, friends, or internet sources 2, 5
• Not addressing the misconception of "eating for two"—only 300 kcal/day additional is needed in second and third trimesters, not double the calories 3
• Ignoring first-trimester weight patterns, as early excessive gain predicts overall high gestational weight gain 3
• Using stigmatizing language when discussing weight, which may cause women to decline weight management support 2, 3