What is the definition of excessive weight gain in pregnancy?

Definition of Excessive Gestational Weight Gain

Excessive gestational weight gain is defined as weight gain during pregnancy that exceeds the Institute of Medicine (IOM) reference ranges based on pre-pregnancy body mass index (BMI): >18 kg for underweight women, >16 kg for normal weight women, >11.5 kg for overweight women, and >9 kg for obese women. 1

BMI-Specific Thresholds for Excessive Weight Gain

The definition is stratified by pre-pregnancy BMI category, as follows:

• **Underweight women (BMI <18.5 kg/m²)**: Excessive gain is >12.5-18 kg total 1, 2
• Normal weight women (BMI 18.5-24.9 kg/m²): Excessive gain is >11.5-16 kg total 1, 2
• Overweight women (BMI 25-29.9 kg/m²): Excessive gain is >7-11.5 kg total 1, 2
• Obese women (BMI ≥30 kg/m²): Excessive gain is >5-9 kg total 1, 2

Alternative Quantitative Definition

Some studies use a simplified threshold definition where excessive gestational weight gain is defined as gaining ≥35 pounds (approximately 16 kg) for normal-weight women and ≥25 pounds (approximately 11.5 kg) for overweight women, regardless of the lower end of the range. 3

Clinical Context and Prevalence

Approximately 40% of normal-weight women and 60% of overweight women gain excessive weight during pregnancy, with the highest rates occurring among younger women (≤19 years old) and nulliparous women. 3 Women with pre-pregnancy overweight or obesity are at consistently higher risk for exceeding these guidelines. 1, 4

Why This Definition Matters for Outcomes

The IOM reference ranges were established because exceeding them is independently associated with serious maternal and neonatal complications that directly impact morbidity and mortality:

Short-term maternal risks:

• Gestational diabetes mellitus 1, 5
• Hypertensive disorders of pregnancy including pre-eclampsia 1, 5
• Higher cesarean section rates 1, 6
• Birth complications and longer hospital stays 1

Short-term neonatal risks:

• Large-for-gestational-age infants 1, 7
• Macrosomia 1, 5, 7
• Neonatal hypoglycemia 1

Long-term consequences:

• Postpartum weight retention and maternal obesity 1
• Increased maternal risk for type 2 diabetes mellitus 1, 5
• Childhood obesity in offspring 1, 7
• Perpetuation of intergenerational obesity cycle 1

Important Clinical Pitfall

The definition is based on total pregnancy weight gain, not rate of gain, though monitoring weekly gain patterns (0.5-0.9 kg/week in second and third trimesters for normal-weight women) helps identify women at risk for exceeding total thresholds. 2, 8 Many clinicians fail to track cumulative weight gain against BMI-specific targets throughout pregnancy, missing opportunities for early intervention. 4

Special Populations

Women carrying multiple gestations (twins, triplets) require higher weight gain targets than these singleton pregnancy thresholds, though the specific definition of "excessive" for multiples is less well-established. 1, 2