For a woman starting pregnancy at a normal weight, the recommended total gain is 25 to 35 pounds. But that number shifts depending on your pre-pregnancy BMI, whether you’re carrying multiples, and how far along you are. The guidelines used across the U.S. come from the Institute of Medicine and are endorsed by both ACOG and the CDC.
Recommended Ranges by Pre-Pregnancy BMI
Your target weight gain depends on your body mass index before pregnancy. The ranges break down into four categories:
- Underweight (BMI below 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 or higher): 11 to 20 pounds
These ranges exist because women who start pregnancy at a higher weight already have more energy reserves stored as body fat. Gaining too far above or below these targets carries real health consequences for both mother and baby.
Where the Weight Actually Goes
If you gain 30 pounds during pregnancy, only a fraction of that is body fat. The rest is your body building and sustaining new tissue, expanding your blood supply, and growing a human. Here’s the approximate breakdown:
- Baby: 7 to 8 pounds
- Placenta: 1.5 pounds
- Amniotic fluid: 2 pounds
- Uterus growth: 2 pounds
- Breast tissue: 1 to 3 pounds
- Increased blood volume: 3 to 4 pounds
- Extra fluid volume: 2 to 3 pounds
- Fat stores: 6 to 8 pounds
That fat isn’t wasted weight. Your body stores it to fuel breastfeeding and recovery after delivery. The blood and fluid increases are necessary to support the placenta and keep your organs functioning while your body does significantly more work than usual.
How Gain Typically Spreads Across Trimesters
Weight gain during pregnancy isn’t linear. In the first trimester, most women gain only 1 to 4 pounds total. Some gain nothing. Some actually lose weight, particularly if morning sickness is severe. Nausea and vomiting affect up to 70% of pregnancies, and in most cases a small loss or no gain during those early weeks is perfectly fine.
The exception is a condition called hyperemesis gravidarum, which is typically diagnosed when a woman loses 5% or more of her pre-pregnancy weight and shows signs of dehydration. If you weighed 150 pounds before pregnancy, that threshold would be a loss of about 7.5 pounds. This level of weight loss can affect the baby’s birth weight and cause problems with thyroid function, liver health, and fluid balance.
The bulk of weight gain happens in the second and third trimesters, when the baby is growing fastest. For women at a normal pre-pregnancy BMI, a steady pace of about 1 pound per week during those later months is a reasonable target. Women who were overweight before pregnancy generally aim for closer to half a pound per week. These are averages, not rules. Week-to-week fluctuations are common and expected, especially as fluid retention increases late in pregnancy.
Weight Gain for Twin Pregnancies
Carrying twins changes the targets significantly. The IOM recommends:
- Normal weight: 37 to 54 pounds
- Overweight: 31 to 50 pounds
- Obese: 25 to 42 pounds
There are no established guidelines for underweight women carrying twins, or for any woman carrying triplets or higher-order multiples. The data simply aren’t sufficient to set firm targets for those pregnancies, so weight management in those cases is handled individually.
Risks of Gaining Too Much
Gaining above the recommended range is the more common pattern in the U.S. Excess weight gain raises the risk of gestational diabetes, preeclampsia (dangerously high blood pressure during pregnancy), and having a larger-than-average baby. A large baby increases the likelihood of a cesarean delivery and can cause complications during labor. After delivery, excess gestational weight gain makes it harder to return to your pre-pregnancy weight, and retained weight between pregnancies compounds the risk for future ones.
The risks aren’t just short-term. Babies born larger than average to mothers with gestational diabetes have a higher chance of developing obesity and metabolic problems later in childhood.
Risks of Gaining Too Little
Gaining below the guidelines carries its own set of concerns. The clearest risk is delivering a baby who is small for gestational age, meaning the baby’s weight falls below the 10th percentile for how far along the pregnancy is. A large meta-analysis published in The BMJ found that severely inadequate weight gain was associated with a 44% higher risk of having a small-for-gestational-age baby compared to women who gained within the recommended range. Moderately low gain also increased the risk, though to a lesser degree.
For younger mothers under 20, insufficient weight gain also raised the risk of preterm birth. Babies born too small or too early face higher rates of breathing problems, difficulty regulating body temperature, and feeding challenges in the newborn period.
Practical Ways to Stay on Track
You don’t need to weigh yourself daily. A check-in at each prenatal appointment is usually enough to spot trends. What matters more than any single weigh-in is the overall trajectory. A sudden jump of several pounds in a week late in pregnancy, for instance, could signal fluid retention related to preeclampsia rather than actual weight gain, and your provider will want to evaluate that.
Calorie needs don’t increase as much as most people assume. In the first trimester, you don’t need any extra calories at all. In the second trimester, an additional 340 calories per day is the general recommendation, rising to about 450 extra calories per day in the third trimester. That’s roughly the equivalent of a yogurt and a piece of fruit, not “eating for two” in any dramatic sense.
If you’re gaining faster than expected, small adjustments to portion sizes and swapping calorie-dense snacks for more filling options (vegetables, whole grains, lean protein) can shift the trend without any kind of restrictive dieting. Pregnancy is not the time to cut calories aggressively. If you’re gaining too slowly despite eating regularly, your provider may look for underlying causes like unmanaged nausea, thyroid changes, or simply not eating enough to meet the increased demands of the second half of pregnancy.