Most women gain about 1 pound per week during the third trimester, which works out to roughly 12 pounds over the final 12 weeks of pregnancy. The exact target depends on your pre-pregnancy BMI and whether you’re carrying one baby or more. Here’s what the numbers look like and where all that weight actually goes.
Weekly and Total Targets by BMI
The guidelines used by most providers come from the Institute of Medicine and are endorsed by the American College of Obstetricians and Gynecologists (reaffirmed in 2023). They set both a total pregnancy gain and an expected weekly rate for the second and third trimesters. The third trimester rate is essentially the same as the second trimester rate, so if you’ve been gaining steadily since week 13, the pace shouldn’t feel different.
- Underweight (BMI under 18.5): about 1 to 1.3 pounds per week, with a total pregnancy gain of 28 to 40 pounds.
- Normal weight (BMI 18.5 to 24.9): about 0.8 to 1 pound per week, with a total pregnancy gain of 25 to 35 pounds.
- Overweight (BMI 25 to 29.9): about 0.5 to 0.7 pounds per week, with a total pregnancy gain of 15 to 25 pounds.
- Obese (BMI 30 or higher): about 0.4 to 0.6 pounds per week, with a total pregnancy gain of 11 to 20 pounds.
These are ranges, not rigid targets. 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 the trimester, not any single weigh-in.
Where the Weight Actually Goes
It’s easy to assume all third trimester weight is baby weight, but the baby accounts for only about half the total. A typical breakdown at delivery looks like this: the baby weighs 7 to 8 pounds, the placenta adds about 1.5 pounds, and amniotic fluid contributes around 2 pounds. Your body also stores 6 to 8 pounds of fat, which serves as an energy reserve for breastfeeding. On top of that, your blood volume, uterus, and breast tissue all expand, adding several more pounds.
The third trimester is when the baby does most of its growing, roughly tripling in weight from about 2 pounds at week 28 to 7 or 8 pounds at birth. So while your scale may jump noticeably during these weeks, a large share of that gain is your baby filling out.
What Happens if You Gain Too Much
Gaining well above the recommended range increases the chance of having a larger-than-average baby (over 8 pounds 13 ounces), which can complicate delivery and raise the likelihood of a cesarean birth. Excess gain also makes it harder to lose weight postpartum and raises the risk of gestational diabetes and high blood pressure during pregnancy. These risks scale gradually. Going a few pounds over the range is not the same as going 20 pounds over.
What Happens if You Gain Too Little
Insufficient gain in the third trimester carries its own risks. A study in The Journal of Nutrition found that women who gained less than about 0.75 pounds per week during the third trimester nearly doubled their risk of preterm delivery, regardless of BMI category. Being underweight before pregnancy compounded the effect, also roughly doubling preterm risk on its own. Low gain can also result in a smaller baby, which is linked to longer hospital stays and feeding difficulties after birth.
If your appetite drops in the last few weeks (common as the baby crowds your stomach), eating smaller, more frequent meals can help you stay on track without forcing large portions.
Calorie Needs in the Third Trimester
The CDC recommends adding about 450 calories per day above your pre-pregnancy intake during the third trimester, up from about 340 extra calories in the second trimester. That 450-calorie increase is roughly equivalent to a peanut butter sandwich and a glass of milk. You don’t need to count precisely, but it helps to know the number is more modest than the “eating for two” cliché suggests.
Quality matters more than quantity. Protein supports the baby’s rapid growth, iron keeps up with your expanded blood supply, and calcium builds the baby’s skeleton. If you’re gaining at the right pace, your calorie intake is probably fine.
Weight Gain With Twins or Multiples
Carrying more than one baby changes the targets significantly. For twins, the recommended total pregnancy gain (not just third trimester) breaks down by BMI:
- Normal weight: 37 to 54 pounds total
- Overweight: 31 to 50 pounds total
- Obese: 25 to 42 pounds total
For triplets, the total target is roughly 58 to 75 pounds, and it climbs from there with higher-order multiples. Much of this gain is front-loaded compared to singleton pregnancies, with providers often aiming for aggressive early gain because twins tend to arrive earlier. A normal-weight woman carrying twins might be expected to reach 37 to 54 pounds by weeks 38 to 40, gaining steadily through the third trimester at a faster clip than she would with a single baby.
Week-to-Week Fluctuations Are Normal
Your weight in the third trimester can swing by 2 to 4 pounds in a single day based on water retention, how recently you ate, and whether your feet are swollen. Many women notice a bigger jump around weeks 34 to 36 as blood volume peaks, then a slight plateau or even a small dip in the final week or two before delivery. None of this is cause for concern on its own.
If you want to track your trend accurately, weigh yourself at the same time of day (morning, after using the bathroom, before eating) and look at the pattern over two to three weeks rather than reacting to any single number. Your provider will also track your weight at prenatal visits, which typically happen every two weeks from week 28 to 36 and then weekly until delivery.