The amount of weight you should gain during pregnancy depends on your pre-pregnancy body mass index (BMI). For a woman starting at a healthy weight (BMI 18.5 to 24.9), the target is 25 to 35 pounds total. Women who start underweight should gain more, and women who start overweight or obese should gain less. These ranges, originally set by the Institute of Medicine and endorsed by both the CDC and the American College of Obstetricians and Gynecologists, remain the standard used in clinical practice today.
Recommended Weight Gain by BMI
Your pre-pregnancy BMI is the single biggest factor in determining your target. Here are the current guidelines 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
These are total gains from conception to delivery. The ranges exist because there’s no single magic number. A woman with a BMI of 25.1 has different needs than one at 29.8, even though both fall in the “overweight” category. Where you fall within the range is something to discuss with your prenatal care provider based on your overall health, age, and how the pregnancy is progressing.
How Fast Should the Weight Come On?
Weight gain isn’t evenly distributed across all nine months. During the first trimester, most women gain only 1 to 4 pounds total. Some gain nothing, or even lose a little due to nausea. That’s normal and not a cause for concern.
The real gains happen in the second and third trimesters. If you started at a healthy weight or were underweight, you should aim for roughly 1 pound per week from that point until delivery. If you started overweight or obese, a slower pace of about half a pound per week is appropriate during those same months.
These weekly targets are averages. Your weight will naturally fluctuate from day to day and week to week based on fluid retention, meals, and bowel habits. A single weigh-in that seems high or low doesn’t mean anything on its own. The overall trend over several weeks is what matters.
Weight Gain Recommendations for Twins
Carrying multiples changes the math significantly. For twins, the recommended total gains are:
- Normal weight (BMI 18.5 to 24.9): 37 to 54 pounds
- Overweight (BMI 25.0 to 29.9): 31 to 50 pounds
- Obese (BMI 30 or higher): 25 to 42 pounds
For underweight women carrying twins, and for anyone carrying triplets or more, there aren’t firm published ranges. These pregnancies need individualized guidance from a care team.
Where the Weight Actually Goes
It’s worth understanding that pregnancy weight gain isn’t just body fat. At full term, the baby typically weighs 6 to 8 pounds. The placenta adds another 1.5 pounds, and amniotic fluid accounts for about 2 pounds. Your blood volume increases by roughly 3 to 4 pounds, and your uterus grows by about 2 pounds. Breast tissue adds another pound or two. Increased fluid in your tissues accounts for several more pounds. The remainder, typically 5 to 8 pounds in a normal-weight pregnancy, is stored fat that your body reserves for breastfeeding and postpartum recovery.
This breakdown explains why gaining “too little” isn’t just about cosmetic concerns. Many of these components are biologically necessary to support a healthy pregnancy and delivery.
What Happens if You Gain Too Much
Gaining above the recommended range carries measurable risks. A large meta-analysis covering 1.6 million women found that exceeding the guidelines was associated with a 37% higher chance of cesarean delivery, a 37% higher risk of high blood pressure disorders during pregnancy, and a 78% increased likelihood of delivering a baby weighing over 8 pounds 13 ounces (a condition called macrosomia). Babies born to mothers who gained excessively were also 26% more likely to need time in the neonatal intensive care unit.
Excess gain also makes it harder to return to your pre-pregnancy weight. Women who overshoot the guidelines are more likely to retain that weight long-term, which raises the risk of complications in future pregnancies and contributes to chronic health issues like type 2 diabetes and heart disease.
What Happens if You Gain Too Little
Insufficient weight gain poses its own serious risks, particularly for the baby. A systematic review of over 3.4 million women found that low total weight gain increased the risk of preterm birth before 37 weeks by 64%. The risk climbed steeply with severity: women with very low gain had nearly four times the risk of delivering before 32 weeks, when prematurity complications are most dangerous.
Low gain also nearly doubled the risk of having a baby with low birth weight (under 5 pounds 8 ounces). Low birth weight babies face higher rates of breathing problems, feeding difficulties, and developmental challenges. The pattern held across both developing and developed countries, suggesting it’s driven by biology rather than access to nutrition alone.
How to Track Your Weight at Home
The CDC recommends weighing yourself once a week throughout pregnancy. For the most consistent readings, weigh yourself without shoes, in lightweight clothing, using the same scale, ideally on the same day and at the same time each week. Morning before eating tends to give the most reliable numbers.
Recording your weight each week and graphing it can help you spot trends early. If you notice you’re consistently above or below the expected pace for several weeks in a row, that’s useful information to bring to a prenatal visit. A single off week is almost always just fluid shifts, especially in the third trimester when swelling in your feet and ankles can add several pounds of water weight overnight.
Keep in mind that these guidelines apply to your total gain from the start of pregnancy to delivery. If you’re unsure of your starting weight, your first prenatal visit weight is typically used as the baseline. Weight loss or restrictive dieting during pregnancy is not recommended for any BMI category. Even for women with obesity, the goal is controlled, slower gain rather than no gain or weight loss.