Healthy Pregnancy Weight Gain: IOM Guidelines
The Institute of Medicine (IOM) published evidence-based gestational weight gain guidelines based on pre-pregnancy BMI. Gaining within the recommended range reduces risks of complications for both mother and baby.
Recommended Total Gain (Singleton Pregnancy)
- Underweight (BMI <18.5): 12.5–18.0 kg (28–40 lb)
- Normal weight (BMI 18.5–24.9): 11.5–16.0 kg (25–35 lb)
- Overweight (BMI 25–29.9): 7.0–11.5 kg (15–25 lb)
- Obese (BMI ≥30): 5.0–9.0 kg (11–20 lb)
Twin Pregnancy
- Normal weight: 17–25 kg
- Overweight: 14–23 kg
- Obese: 11–19 kg
Gain by Trimester
Weight gain is not linear. Most guidelines recommend:
- First trimester: 0.5–2 kg total (fetus is tiny; nausea often limits intake)
- Second and third trimesters: ~0.35–0.5 kg per week for normal-weight women
Where the Weight Goes
Of 13 kg total gain: fetus ~3.3 kg, placenta ~0.7 kg, amniotic fluid ~0.8 kg, uterus ~0.9 kg, breasts ~0.5 kg, blood volume ~1.4 kg, body fluids ~1.8 kg, maternal fat stores ~3.5 kg.
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