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IOM Guidelines

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Institute of Medicine Gestational Weight Gain Guidelines (2009)

The 2009 recommendations by the US Institute of Medicine (now National Academy of Medicine) specifying healthy gestational weight gain ranges by pre-pregnancy BMI category.

Definition

The IOM Guidelines refer to the 2009 report by the Institute of Medicine (now the National Academy of Medicine) titled "Weight Gain During Pregnancy: Reexamining the Guidelines." This report updated the 1990 IOM recommendations and established the gestational weight gain targets that are used worldwide by obstetricians, midwives, and maternal health researchers.

The guidelines stratify recommended total weight gain and weekly gain rates by pre-pregnancy BMI, recognising that a single universal target is inappropriate across the range of starting body compositions.

Key Things to Know

  • IOM targets use pre-pregnancy BMI — always anchor to weight before conception, not current pregnancy weight.
  • The Pregnancy BMI Calculator applies these guidelines and shows your on-track status in real time.
  • First trimester gain is not included in weekly rate targets — the 0.35–0.50 kg/week applies to the 2nd and 3rd trimesters only.
  • These are population-level guidelines, not individual prescriptions. Your OB-GYN may adjust based on foetal growth scans, clinical findings, and your specific nutritional status.

Related Calculators

Pregnancy BMI Calculator →Calculate your pre-pregnancy BMI and get IOM-recommended gestational weight gain range. Track your current pregnancy weight gain and stay on target for a healthy pregnancy.
BMI Calculator →Calculate your BMI instantly using kg/lbs and cm/ft. Includes BMI category and healthy weight range using WHO standards.

Related Terms

Gestational Weight GainGestational Weight Gain (GWG)BMIBody Mass IndexPre-eclampsiaPre-eclampsiaPreterm BirthPreterm Birth (Premature Birth)

Frequently Asked Questions

The IOM 2009 guidelines were developed primarily from Western population data. Some researchers argue Indian women may need adjusted targets because Indians tend to have higher body fat percentage at lower BMI values (the 'thin-fat Indian' phenotype). The Indian Council of Medical Research (ICMR) has not yet published separate BMI-based gestational weight gain guidelines for Indian women, so most Indian OB-GYNs apply IOM targets with clinical adjustment for individual patients.
Under-gaining below the IOM minimum is associated with preterm birth, intrauterine growth restriction (IUGR), and low birth weight. Over-gaining above the IOM maximum is linked to gestational diabetes, pre-eclampsia, large-for-gestational-age babies, and increased caesarean rates. Both deviations are gradients — 1 kg outside range is different from 8 kg outside. Discuss any significant deviation with your OB-GYN. Track your current gain with the [Pregnancy BMI Calculator](/pregnancy-bmi-calculator/).
The IOM 2009 report includes separate twin pregnancy guidelines: Normal BMI: 17–25 kg total; Overweight: 14–23 kg; Obese: 11–19 kg. These are significantly higher than singleton targets due to two foetuses, two placentas, and greater blood volume expansion. Underweight women carrying twins do not have a defined IOM range — individualised guidance from a maternal-foetal medicine specialist is recommended.