Expected Weight Gain in First Trimester of Pregnancy
A normal-weight woman should gain 1.4-2.3 kg (3.1-5.1 pounds) during the first trimester of pregnancy, with weight gain recommendations varying based on pre-pregnancy BMI. 1
Weight Gain Recommendations by Pre-Pregnancy BMI
Weight gain during pregnancy should follow a pattern based on a woman's pre-pregnancy BMI:
Underweight women (BMI <19.8):
- Total recommended gain: Up to 18 kg (40 lbs)
- First trimester: 1.4-2.3 kg
Normal weight women (BMI 19.8-26):
- Total recommended gain: 11.5-16 kg (25-35 lbs)
- First trimester: 1.4-2.3 kg
Overweight women (BMI 26-29):
- Total recommended gain: <50% of normal weight recommendations
- First trimester: Approximately 0.7-1.2 kg
Obese women (BMI >30):
- Total recommended gain: 7 kg (15 lbs)
- First trimester: Minimal gain recommended
Trimester-Specific Patterns
Recent research challenges traditional assumptions about first trimester weight gain. A prospective study found that contrary to previous reports, mean maternal weight and body composition values remain unchanged in the first trimester of pregnancy 2. This suggests that significant weight gain may not begin until after 14 weeks gestation.
Energy Requirements During First Trimester
Unless a woman begins pregnancy with depleted body reserves, energy needs do not typically increase during the first trimester 1. The additional caloric requirements (approximately 300 kcal/day) are generally only needed during the second and third trimesters to support:
- Increases in maternal blood volume
- Growth of breast, uterus, and adipose tissue
- Placental growth
- Fetal growth
- Amniotic fluid production
Clinical Implications
- Weight gain should be steady and progressive throughout pregnancy 1
- First trimester weight gain is typically minimal compared to later trimesters
- Weight monitoring should begin early in pregnancy using accurate measurements, not self-reported pre-pregnancy weights 2
- Calculation of BMI and gestational weight gain should be based on accurate early pregnancy measurements 2
Potential Pitfalls in Weight Management
- Failing to establish an accurate baseline weight early in pregnancy
- Not adjusting weight gain expectations based on pre-pregnancy BMI
- Overlooking the importance of quality nutrition despite minimal caloric increase needs in first trimester
- Not recognizing that excessive first trimester weight gain may indicate risk for exceeding total recommended weight gain
Proper weight gain during pregnancy is important for optimal maternal and fetal outcomes, as both inadequate and excessive weight gain are associated with adverse pregnancy outcomes including gestational diabetes, pre-eclampsia, and delivery complications 1.