Most women gain about 1 pound per week during the third trimester, which means roughly 12 to 14 pounds between week 28 and delivery. That number varies based on your pre-pregnancy weight, though. The third trimester is when your baby is growing fastest, your blood volume peaks, and your body is storing fluid and energy for labor and breastfeeding, so this is typically the period with the steepest weight gain.
Total Pregnancy Targets by BMI
The CDC bases its weight gain recommendations on your pre-pregnancy BMI. About half of total pregnancy weight gain happens in the third trimester, so you can use these overall targets to estimate where you should be heading into the final stretch:
- Underweight (BMI under 18.5): 28 to 40 pounds total
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds total
- Overweight (BMI 25.0 to 29.9): 15 to 25 pounds total
- Obese (BMI 30.0 to 39.9): 11 to 20 pounds total
If you started pregnancy at a normal weight and have gained about 15 to 20 pounds by the end of the second trimester, you’re looking at gaining another 10 to 15 pounds over the final 12 weeks. Women who were overweight before pregnancy typically gain less per week in the third trimester, closer to half a pound to three-quarters of a pound.
What That Weight Actually Is
The number on the scale during the third trimester can feel alarming, but very little of it is body fat. By the time you deliver, the baby alone accounts for 6 to 8 pounds. The placenta adds about 1.5 pounds. Amniotic fluid contributes roughly 2 pounds. Your blood volume increases by about 3 to 4 pounds, and your body retains several extra pounds of fluid in your tissues, which is why swelling in the feet and ankles is so common late in pregnancy. Your uterus, which started the size of a pear, now weighs about 2 pounds on its own. Breast tissue growth adds another pound or two.
Some fat storage is normal and expected. Your body builds reserves to fuel labor and postpartum recovery. This usually accounts for 5 to 9 pounds of total pregnancy weight gain, and much of it accumulates in the second and third trimesters.
Week-by-Week Patterns
Weight gain in the third trimester isn’t perfectly steady. Many women notice a burst of gain between weeks 28 and 35, when the baby is putting on about half a pound per week. During weeks 36 to 40, the rate often slows slightly as the baby’s growth plateaus and some women even lose a pound or two right before labor as fluid shifts occur.
It’s also normal for the scale to jump 2 or 3 pounds in a single week and then barely move the next. Day-to-day fluctuations of 1 to 3 pounds are almost always water retention, not actual tissue gain. Eating a salty meal, standing for long periods, or being slightly dehydrated can all cause temporary spikes. Weighing yourself at the same time of day, in similar clothing, gives you a more reliable trend.
Twin Pregnancies
If you’re carrying twins, the targets are significantly higher. A woman who started at a normal weight should gain 37 to 54 pounds total, according to the CDC. For overweight women carrying twins, the range is 31 to 50 pounds. Much of that additional gain happens in the third trimester, when two babies are growing simultaneously and fluid volumes are even greater.
The CDC provides week-by-week tracking charts for twin pregnancies specifically, with a shaded target zone. If your weight falls outside that zone in either direction, small adjustments to diet and activity can help, but you should not try to lose weight during pregnancy.
When Gain Is Too Low
Gaining less than expected in the third trimester raises real concerns. Low maternal weight gain is linked to babies being born smaller than expected for their gestational age, a condition that can lead to complications after birth. For underweight and normal-weight women, the association is strongest. Inadequate gain in underweight women also increases the risk of preterm birth.
Weight loss during pregnancy carries even more serious risks, including stillbirth and neonatal death. If you’re struggling to gain weight because of nausea, food aversions, or appetite loss late in pregnancy, that’s worth flagging at a prenatal visit. Small, frequent, calorie-dense meals (nuts, avocado, full-fat dairy, smoothies) can help when large meals feel impossible.
When Gain Is Higher Than Expected
Gaining more than the recommended range isn’t uncommon. About half of pregnant women in the U.S. gain more than guidelines suggest. Excess gain in the third trimester increases the chance of a larger baby, which can complicate delivery, and makes it harder to return to your pre-pregnancy weight afterward. It also raises the risk of gestational diabetes and preeclampsia if those conditions haven’t already been screened for.
That said, a single high week on the scale doesn’t mean you’ve gained too much. Rapid weight gain of more than 2 pounds in a week, especially if it comes with swelling in the face or hands, headaches, or vision changes, can be a sign of preeclampsia and needs prompt evaluation. Gradual gain that’s a few pounds above target is a different situation entirely and is usually managed with modest dietary adjustments.
Calorie Needs in the Third Trimester
Your body needs roughly 450 extra calories per day in the third trimester compared to your pre-pregnancy intake. That’s more than the second trimester (about 340 extra calories) and substantially more than the first trimester, when calorie needs barely change. To put 450 calories in perspective, that’s a cup of Greek yogurt with granola and a banana, or a peanut butter sandwich with a glass of milk.
The quality of those calories matters more than hitting an exact number. Protein needs increase significantly in the third trimester because the baby is building muscle and organ tissue rapidly. Iron needs are also higher because of expanded blood volume. If you’re eating regular meals and snacks with a mix of protein, whole grains, and produce, you’re likely meeting the mark without counting anything.