Most pregnancy weight gain happens in the second and third trimesters, with very little expected in the first. If you start at a healthy weight (BMI 18.5 to 24.9), the total target is 25 to 35 pounds over the full pregnancy, but how that distributes across the three trimesters is uneven. Your first trimester accounts for just 1 to 4 pounds, while the bulk of the gain comes steadily over the final six months.
Total Targets Based on Pre-Pregnancy Weight
Your recommended total gain depends on your BMI before you became pregnant. The Institute of Medicine guidelines, used by most OB-GYN practices in the U.S., break it down like this:
- Underweight (BMI under 18.5): 28 to 40 pounds
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds
- Overweight (BMI 25 to 29.9): 15 to 25 pounds
- Obese (BMI 30 or higher): 11 to 20 pounds
These ranges exist because the risks of gaining too much or too little shift depending on where you start. A person who is underweight needs more stored energy to support fetal growth, while someone at a higher BMI already has those reserves.
First Trimester: 1 to 4 Pounds
During the first 13 weeks, most people don’t need to gain much weight at all. The typical range is about 1 to 4 pounds total for the entire trimester. Some people gain nothing, and some even lose a few pounds due to nausea and food aversions. That’s generally fine as long as you’re staying hydrated and eating when you can.
Your baby is still tiny at this point, smaller than a lime by week 13. The calorie demands of pregnancy haven’t ramped up yet, so you don’t need extra calories in the first trimester. Eating the same amount you normally would is enough for most people.
Second Trimester: About 1 Pound Per Week
This is when weight gain picks up noticeably. For someone at a normal pre-pregnancy BMI, the target is roughly 1 pound per week through weeks 14 to 27. That works out to about 12 to 14 pounds over the trimester. If you started overweight, the pace is closer to half a pound per week. Underweight individuals may aim for slightly more than a pound weekly.
The second trimester is when your blood volume expands significantly, the placenta grows to full size, and your baby goes from a few ounces to about 2 pounds. You’ll also start building the fat stores your body uses to fuel breastfeeding later. Calorie needs increase by about 300 to 350 extra calories per day during this period, roughly the equivalent of a yogurt parfait and a piece of fruit.
Third Trimester: Steady Gain, Then a Plateau
Weight gain in the third trimester continues at roughly the same weekly pace as the second, around 1 pound per week for normal-weight individuals. You can expect to gain another 8 to 14 pounds between week 28 and delivery. Many people notice the gain slows or stops in the final week or two before birth, which is normal.
Your baby is doing the most rapid growing during these last 12 weeks, going from about 2 pounds to an average of 7 to 8 pounds at birth. A significant portion of the weight you gain in the third trimester is the baby, plus increased amniotic fluid and additional blood volume. Swelling in your feet and legs can also add a few pounds of water weight that disappears quickly after delivery.
Where the Weight Actually Goes
If you gain 30 pounds during pregnancy, only about 7 to 8 of those pounds are baby. The rest supports the pregnancy in ways your body needs:
- Placenta: 1.5 to 2 pounds
- Amniotic fluid: about 2 pounds
- Increased blood volume: 3 to 4 pounds
- Uterine growth: about 2 pounds
- Breast tissue: 1 to 2 pounds
- Maternal fat and nutrient stores: 6 to 8 pounds
- Extra fluid in tissues: 3 to 4 pounds
Understanding this breakdown helps explain why the number on the scale can feel high even when your baby is still small. Much of that weight is blood, fluid, and tissue that your body sheds in the weeks after delivery.
Twin Pregnancy Targets
If you’re carrying twins, the recommendations are higher across the board. Normal-weight individuals should aim for 37 to 54 pounds total. Overweight individuals have a target of 31 to 50 pounds, and those with a BMI of 30 or above should aim for 25 to 42 pounds. The gain also tends to front-load more than in singleton pregnancies, with providers often encouraging steady weight gain from early in the second trimester rather than waiting for it to ramp up naturally.
Risks of Gaining Too Much or Too Little
Gaining more than the recommended range increases the chance of having a larger-than-average baby, which raises the likelihood of a cesarean delivery and can cause complications during labor. Excess gain is also linked to higher rates of gestational diabetes and high blood pressure during pregnancy. After delivery, the extra weight becomes harder to lose, and research consistently shows that excessive pregnancy gain is one of the strongest predictors of long-term weight retention.
Gaining too little carries its own risks. Inadequate weight gain is associated with low birth weight, meaning a baby born under 5 pounds 8 ounces. Low-birth-weight babies face higher rates of breathing problems, infections, and feeding difficulties in the newborn period. They’re also at greater risk for preterm birth. This is why the ranges exist as floors, not just ceilings.
Tracking Without Obsessing
Your provider will weigh you at each prenatal visit, which typically means monthly through week 28 and then every two weeks or weekly until delivery. That schedule gives you plenty of data points without the stress of daily weigh-ins at home. If you do weigh yourself between appointments, pick the same time of day (morning is most consistent) and the same scale. Don’t react to a single reading, because day-to-day fluctuations of 2 to 3 pounds are completely normal and usually reflect water retention, digestion, or timing.
The weekly targets are averages, not rules. You might gain 3 pounds one week and nothing the next. What matters is the overall trend across weeks, not any individual number. If your gain is consistently above or below the expected curve, your provider can adjust your nutrition plan or check for underlying causes like fluid retention or gestational diabetes.