Weight Gain In Pregnancy — What’s Recommended?
Welcome back for another episode! Today, we’re talking about a key topic in prenatal care: maternal weight gain in pregnancy.
Before we jump in, a quick reminder: There’s still one more chance to attend my live training, “The Intern’s Guide to Managing Labor.”
I’ll walk you through how to calculate, implement, and use labor curves to manage inductions and augmentations from start to finish. I’ve already hosted two sessions, and the feedback has been great—people found it super helpful. If you want in, check out the link in the show notes or head to subscribepage.io/interntraining.
Where Do These Guidelines Come From?
A few decades back, in 1990, the Institute of Medicine (IOM) came out with recommendations for how much weight should be gained during pregnancy. These were updated in 2009, and that’s what I’ll be referencing today.
So why were these guidelines created? Over time, it became clear from the literature that both too little and too much weight gain during pregnancy came with risks. Women who started pregnancy with a low BMI and gained too little weight were more likely to deliver preterm, have small-for-gestational-age (SGA) infants, or experience perinatal mortality. But when those same women gained too much weight, they faced higher risks of delivering large-for-gestational-age (LGA) infants and retaining more weight postpartum.
So the IOM developed standardized parameters to guide clinical counseling and (ideally) improve outcomes.
BMI Categories: A Quick Review
Before diving into the recommendations, let’s revisit the World Health Organization’s BMI classifications:
Underweight: <18.5 kg/m²
Normal weight: 18.5–24.9 kg/m²
Overweight: 25–29.9 kg/m²
Obese (Class I): 30–34.9 kg/m²
Obese (Class II): 35–39.9 kg/m²
Obese (Class III): ≥40 kg/m²
While we categorize obesity into three classes, current weight gain recommendations apply to all obesity classes as a single group due to limited data.
Recommended Weight Gain by BMI
Here are the IOM guidelines for singleton pregnancies:
Underweight (BMI: <18.5 kg/m²): 28–40 lbs
Normal weight (BMI: 18.5–24.9 kg/m²): 25–35 lbs
Overweight (BMI: 25–29.9 kg/m²): 15–25 lbs
Obese (BMI: >30 kg/m²): 11–20 lbs
You might wonder why the minimum recommendation for obese patients isn’t even lower. That’s because these values mostly reflect physiologic pregnancy changes—including about 12–14 lbs of water, 2 lbs of protein, and a modest amount of fat.
Also, some studies show that gaining less than recommended can increase the risk of SGA infants—even in overweight or obese patients. That said, if fetal growth is appropriate, pushing weight gain just to meet these numbers isn’t backed by evidence.
What About Twins?
The 2009 IOM update also includes weight gain recommendations for twin pregnancies:
Normal weight (BMI: 18.5–24.9 kg/m²): 37–54 lbs
Overweight (BMI: 25–29.9 kg/m²): 31–50 lbs
Obese (BMI: >30 kg/m²): 25–42 lbs
There's no data yet to guide recommendations for higher-order multiples (triplets or more).
