Most pregnant women should gain between 11 and 40 pounds total, depending on their pre-pregnancy weight. The range is wide because your starting body mass index (BMI) is the single biggest factor in determining your personal target. A woman who begins pregnancy underweight needs to gain significantly more than a woman who begins at a higher weight.
Recommended Weight Gain by BMI
The guidelines used by most doctors in the United States come from the Institute of Medicine (IOM), and they’re endorsed by the American College of Obstetricians and Gynecologists. They break down like this for a single baby:
- Underweight (BMI under 18.5): 28 to 40 pounds
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds
- Overweight (BMI 25.0 to 29.9): 15 to 25 pounds
- Obese (BMI 30.0 to 39.9): 11 to 20 pounds
Your BMI before pregnancy is what matters here, not your BMI at your first prenatal visit. If you’re not sure of yours, you can calculate it by dividing your weight in pounds by your height in inches squared, then multiplying by 703. Or just plug your numbers into any online BMI calculator.
When the Weight Should Come On
Weight gain during pregnancy isn’t evenly spread across all nine months. In the first trimester, most women gain only 1 to 4 pounds total. Some women lose weight early on due to nausea, and that’s generally not a concern as long as the pattern picks up later.
The real gains happen in the second and third trimesters, when you’re building blood volume, growing a placenta, and the baby is putting on the bulk of its weight. During those final two trimesters, a normal-weight woman typically gains about a pound per week. Overweight women aim for closer to half a pound per week, while underweight women may need slightly more than a pound. These are averages. Week to week, your weight will fluctuate based on fluid retention, meals, and other factors that have nothing to do with how the pregnancy is progressing.
Where the Weight Actually Goes
If you’re gaining 30 pounds and the baby weighs 7 or 8 of those, you might wonder what accounts for the rest. The answer is that pregnancy reshapes nearly every system in your body, and all of it weighs something.
A rough breakdown for a typical pregnancy looks like this: the baby accounts for about 7 to 8 pounds. The placenta adds around 1.5 pounds. Amniotic fluid contributes about 2 pounds. Your uterus grows to roughly 2 pounds heavier than its pre-pregnancy size. Breast tissue adds 1 to 3 pounds. Your blood volume increases by 3 to 4 pounds, and additional fluid in your tissues accounts for another 2 to 3 pounds. The remaining 6 to 8 pounds is fat your body stores as an energy reserve for labor, recovery, and breastfeeding.
That fat storage is intentional. Women who start pregnancy underweight tend to store more fat (around 13 pounds), while women who start at a higher weight store less. Women who begin pregnancy obese and gain within the recommended range may actually lose a small amount of body fat over the course of the pregnancy, even as total weight increases from everything else.
Weight Gain Targets for Twins
Carrying twins changes the math significantly. The IOM guidelines for twin pregnancies are:
- Normal weight: 37 to 54 pounds
- Overweight: 31 to 50 pounds
- Obese: 25 to 42 pounds
For triplets or higher-order multiples, there isn’t enough data to set official targets. Your provider will monitor your gain individually. With twins, the weekly pace is faster too. Normal-weight women carrying twins aim for roughly 1 to 1.4 pounds per week over the course of the pregnancy, while overweight women target about 0.8 to 1.4 pounds and obese women about 0.7 to 1.1 pounds per week.
Risks of Gaining Too Much
Going well above the recommended range isn’t just a cosmetic concern. Excessive weight gain during pregnancy is linked to pregnancy-related high blood pressure (including preeclampsia), gestational diabetes, and having a baby that’s larger than normal for its gestational age. A very large baby increases the odds of a difficult delivery, shoulder injuries during birth, and a higher likelihood of cesarean section.
There’s also the longer-term picture. Women who gain more than recommended are more likely to retain that weight after delivery, which raises the risk of entering a future pregnancy at a higher BMI. That compounds the risks for each subsequent pregnancy. Excessive gain can also make it harder to establish breastfeeding, though the reasons for that link aren’t fully understood.
Risks of Gaining Too Little
Gaining less than the guidelines recommend carries its own set of problems, particularly for the baby. Women who fall short of the recommended range are roughly twice as likely to have a low-birth-weight infant and about 1.5 to 1.8 times more likely to deliver preterm (before 37 weeks). In developed countries, the risk of a very small baby is even more pronounced, with some research showing a threefold increase in low birth weight among women with inadequate gain.
Preterm and low-birth-weight babies face higher rates of breathing problems, feeding difficulties, and longer hospital stays after delivery. This is why providers track weight gain at every prenatal appointment. If you’re consistently falling below your target, your provider may look at whether you’re eating enough calories, whether nausea is limiting your intake, or whether there’s an underlying issue affecting nutrient absorption.
What Healthy Gain Looks Like in Practice
The guidelines are ranges, not exact targets, and your body won’t gain weight in a perfectly smooth line. A week where you gain two pounds followed by a week where you gain nothing is completely normal. What matters is the overall trend across weeks and months, not any single weigh-in.
You don’t need to eat for two in the literal sense. In the first trimester, most women don’t need any extra calories at all. In the second trimester, an additional 300 to 350 calories per day covers the increased demand. By the third trimester, that rises to about 400 to 500 extra calories. For reference, 300 calories is roughly a cup of yogurt with some fruit and granola.
If you’re gaining faster than expected, small adjustments to portion sizes and swapping calorie-dense snacks for more filling, nutrient-rich options can slow the pace without restricting your diet. If you’re not gaining enough, adding calorie-dense but nutritious foods like nuts, avocado, cheese, and whole grains can help bridge the gap. The goal in either case is steady, gradual progress toward your range, not a dramatic correction in either direction.