Pregnancy Weight Gain: How Much Is Healthy?

Recommended pregnancy weight gain isn't a single number — it depends heavily on your pre-pregnancy body mass index and whether you're carrying one baby or multiples. This guide breaks down the official Institute of Medicine guidelines, explains why the targets vary so much by starting weight, and covers the health risks on both ends of the range.

By the FitCalcHub Editorial Team — Updated September 2026 — 8 min read

IOM 2009 Pregnancy Weight Gain Guidelines by BMI

The most widely used pregnancy weight gain guidelines come from the U.S. Institute of Medicine (IOM, now the National Academy of Medicine), updated in 2009. Recommended total gain for a singleton pregnancy is based on your pre-pregnancy BMI category — the higher your starting BMI, the lower the recommended additional weight gain, because higher pre-pregnancy body fat stores already provide additional energy reserve for pregnancy and lactation.

Pre-Pregnancy BMI Category	BMI (kg/m²)	Recommended Total Gain (Singleton)
Underweight	<18.5	12.5–18 kg (28–40 lb)
Normal weight	18.5–24.9	11.5–16 kg (25–35 lb)
Overweight	25–29.9	7–11.5 kg (15–25 lb)
Obese	≥30	5–9 kg (11–20 lb)

Not sure where your pre-pregnancy BMI falls? Use our BMI Calculator with your pre-pregnancy weight, then apply your Pregnancy Weight Gain Calculator to see your full recommended range and trimester-by-trimester pacing.

Based on: Institute of Medicine (US) and National Research Council (US) Committee to Reexamine IOM Pregnancy Weight Guidelines; Rasmussen KM, Yaktine AL, eds. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press; 2009. PubMed ↗

Singleton vs Twin Pregnancy: Different Targets

Twin and higher-order multiple pregnancies require substantially more total weight gain to support healthy fetal growth for each baby. The IOM provides separate provisional guidance for twin pregnancies, since less research exists for multiples compared to singleton pregnancies:

Pre-Pregnancy BMI Category	Recommended Total Gain (Twins)
Normal weight	17–25 kg (37–54 lb)
Overweight	14–23 kg (31–50 lb)
Obese	11–19 kg (25–42 lb)

Risks of Gaining Too Much or Too Little Weight

Both ends of the range carry documented risks, which is why the guidelines exist as a range rather than a single target:

Gaining too little is associated with higher risk of low birth weight, preterm birth, and a baby small for gestational age.
Gaining too much is associated with higher risk of gestational diabetes, preeclampsia, cesarean delivery, a baby large for gestational age, and greater difficulty returning to pre-pregnancy weight postpartum.
Both extremes are associated with a somewhat higher risk of the child developing obesity later in life, according to observational research, though many other factors also contribute.

Weight gain pacing matters as much as the total: most guidelines recommend a modest 0.5–2 kg gain in the first trimester, followed by roughly 0.35–0.5 kg per week in the second and third trimesters for normal-weight individuals (lower weekly pace for higher BMI categories).

How to Use the Pregnancy Weight Gain Calculator

Enter your pre-pregnancy weight and height (or BMI directly) plus whether you're carrying a singleton or twins into our Pregnancy Weight Gain Calculator to get your personalised total range and an approximate weekly pacing guide. This is a general educational reference — always follow your obstetric provider's individualised guidance over general population recommendations, since they account for your specific health history and any pregnancy complications.

For guidance on safe activity levels alongside healthy weight gain, see our Exercising Safely During Pregnancy guide.

Frequently Asked Questions

How much weight should I gain during pregnancy?

Recommended total weight gain depends on your pre-pregnancy BMI: 12.5-18 kg if underweight, 11.5-16 kg if normal weight, 7-11.5 kg if overweight, and 5-9 kg if obese, based on IOM 2009 guidelines for singleton pregnancies.

Why do heavier women need to gain less weight during pregnancy?

Higher pre-pregnancy BMI is associated with greater existing energy reserves, so less additional weight gain is needed to support a healthy pregnancy. The guidelines aim to balance adequate fetal growth against the higher risks of gestational diabetes and other complications associated with excess gain at higher starting weights.

How much weight gain is recommended for twin pregnancies?

For twin pregnancies, IOM provisional guidance recommends 17-25 kg for normal pre-pregnancy weight, 14-23 kg for overweight, and 11-19 kg for obese categories — substantially more than singleton pregnancy targets to support the growth of two babies.

What happens if I gain too little weight during pregnancy?

Gaining less than the recommended range is associated with higher risk of low birth weight, preterm birth, and a baby that is small for gestational age.

What happens if I gain too much weight during pregnancy?

Gaining more than the recommended range is associated with higher risk of gestational diabetes, preeclampsia, cesarean delivery, a baby large for gestational age, and more difficulty returning to pre-pregnancy weight after birth.

How much weight should I gain per week during pregnancy?

Most guidelines recommend a modest 0.5-2 kg total gain in the first trimester, followed by approximately 0.35-0.5 kg per week in the second and third trimesters for normal-weight individuals, with a lower weekly pace recommended for higher pre-pregnancy BMI categories.

Should I use my pre-pregnancy weight or current weight to calculate my target?

Use your pre-pregnancy weight and BMI to determine your recommended total gain range. Your current weight during pregnancy is then compared against your pre-pregnancy starting point to track progress against that target.

Are pregnancy weight gain guidelines the same for everyone?

The IOM guidelines are general population recommendations based on pre-pregnancy BMI and number of babies. Individual health conditions, pregnancy complications, and your obstetric provider's specific guidance should always take precedence over general guidelines.

Does gaining outside the recommended range affect the baby's long-term health?

Observational research links both excessive and insufficient pregnancy weight gain to a somewhat higher risk of the child developing obesity later in life, though many other genetic and environmental factors also contribute, and this should not be a source of excessive worry over a single measurement.

This article is part of our complete General Health Guide.

Medical Disclaimer: This article is for educational purposes only and is not medical advice. Always follow your obstetric provider's individualised guidance on weight gain, nutrition, and pregnancy management, which accounts for your specific health history and any complications.

Scientific References

Institute of Medicine (US) and National Research Council (US) Committee to Reexamine IOM Pregnancy Weight Guidelines; Rasmussen KM, Yaktine AL, eds. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press; 2009. PubMed ↗
American College of Obstetricians and Gynecologists. "Weight Gain During Pregnancy." Committee Opinion No. 548. Obstet Gynecol. 2013;121(1):210-212. PubMed ↗