1How Much Weight Should You Gain During Pregnancy?
Healthy gestational weight gain (GWG) depends primarily on your pre-pregnancy body mass index (BMI). The Institute of Medicine (IOM) — now the National Academy of Medicine — published evidence-based guidelines in 2009 that remain the global clinical standard. These guidelines are endorsed by ACOG, WHO, and NICE.
The recommendations differ for singleton and twin pregnancies because twins place substantially higher nutritional and metabolic demands on the body. Women carrying twins require greater weight gain across all BMI categories to support optimal fetal growth.
| Pre-pregnancy BMI | BMI Category | Singleton Gain | Twin Gain | Rate (2nd & 3rd Tri) |
|---|---|---|---|---|
| <18.5 | Underweight | 28–40 lb (12.5–18 kg) | 50–62 lb (23–28 kg)* | 1.0–1.3 lb/wk (0.45–0.6 kg) |
| 18.5–24.9 | Normal weight | 25–35 lb (11.5–16 kg) | 37–54 lb (17–25 kg) | 0.8–1.0 lb/wk (0.35–0.45 kg) |
| 25.0–29.9 | Overweight | 15–25 lb (7–11.5 kg) | 31–50 lb (14–23 kg) | 0.5–0.7 lb/wk (0.23–0.32 kg) |
| ≥30.0 | Obese | 11–20 lb (5–9 kg) | 25–42 lb (11–19 kg) | 0.4–0.6 lb/wk (0.18–0.27 kg) |
*Limited data for underweight women with twin pregnancies. Consult your healthcare provider.
First Trimester Weight Gain
During the first trimester (weeks 1–13), total weight gain is modest regardless of BMI. Most guidelines suggest a total of 1–4 lb (0.5–2 kg) over the entire first trimester. Weight gain accelerates in the second trimester as the placenta, amniotic fluid, and fetal tissues grow rapidly. Some women lose weight in the first trimester due to nausea and vomiting — this is generally not a concern if weight gain recovers in the second trimester.
Where Does the Weight Go?
The total weight gained during pregnancy is distributed across many components — not just the baby. For a woman gaining approximately 30 lb (13.6 kg):
- Baby: ~7–8 lb (3.2–3.6 kg)
- Placenta: ~1.5 lb (0.7 kg)
- Amniotic fluid: ~2 lb (0.9 kg)
- Uterus growth: ~2 lb (0.9 kg)
- Breast tissue: ~2 lb (0.9 kg)
- Blood volume increase: ~4 lb (1.8 kg)
- Fluid and tissue: ~4 lb (1.8 kg)
- Maternal fat stores: ~7 lb (3.2 kg)
2References
Last medical review: May 2025 · RxMedCalc Clinical Editorial Team.
3Frequently asked questions
How much weight should I gain during pregnancy?
According to IOM 2009 guidelines: underweight (BMI <18.5): 28–40 lb (12.5–18 kg); normal weight (BMI 18.5–24.9): 25–35 lb (11.5–16 kg); overweight (BMI 25–29.9): 15–25 lb (7–11.5 kg); obese (BMI ≥30): 11–20 lb (5–9 kg).
How much weight should I gain per week during pregnancy?
In the first trimester, total gain of 1–4 lb (0.5–2 kg) is typical. From the second trimester onward, normal-weight women should gain approximately 1 lb (0.45 kg) per week. Overweight women should aim for about 0.6 lb/week and obese women about 0.5 lb/week.
What happens if I gain too much weight during pregnancy?
Excessive gestational weight gain increases the risk of gestational diabetes, preeclampsia, caesarean delivery, large-for-gestational-age babies, and difficulty losing weight after delivery. It also raises the child's long-term risk of obesity.
Can I diet during pregnancy?
Calorie restriction during pregnancy is not recommended. However, eating a balanced diet, avoiding excessive added sugars and ultra-processed foods, and gentle physical activity are safe and recommended for all BMI categories to support healthy weight gain.
Medical disclaimer: This calculator is for educational and clinical decision-support purposes only. It does not replace clinical judgment or specialist consultation. RxMedCalc is not liable for clinical decisions made solely on this tool.