Most women gain about 1 pound per week during the third trimester, though the exact target depends on your pre-pregnancy BMI. For a woman who started pregnancy at a normal weight, total pregnancy weight gain should fall between 25 and 35 pounds, with roughly a third of that arriving in the final 13 weeks. Here’s what to expect and what all that weight actually consists of.
Weekly and Total Targets by BMI
Weight gain recommendations are built around your BMI before pregnancy. The Institute of Medicine guidelines, endorsed by ACOG, break it down like this:
- Underweight (BMI under 18.5): 28 to 40 pounds total, roughly 1 to 1.3 pounds per week in the second and third trimesters
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds total, about 1 pound per week in the second and third trimesters
- Overweight (BMI 25 to 29.9): 15 to 25 pounds total, about 0.6 pounds per week in later trimesters
- Obese (BMI 30 or higher): 11 to 20 pounds total, about 0.5 pounds per week in later trimesters
These ranges cover the entire pregnancy, but since first-trimester gain is typically only 1 to 5 pounds, the third trimester carries a large share. If you’re at a normal pre-pregnancy weight, expect to gain somewhere around 10 to 14 pounds between weeks 28 and 40.
Where the Weight Actually Goes
The number on the scale can feel alarming if you don’t realize how little of it is body fat. A full-term baby accounts for 7 to 8 pounds on its own. The rest distributes across your body in ways that support the pregnancy:
- Placenta: about 1.5 pounds
- Amniotic fluid: about 2 pounds
- Uterus growth: about 2 pounds
- Breast tissue: 1 to 3 pounds
- Extra blood volume: 3 to 4 pounds
- Extra fluid volume: 2 to 3 pounds
- Fat stores: 6 to 8 pounds
That adds up to roughly 25 to 31 pounds for a normal-weight pregnancy. Much of this weight, especially blood volume, fluid, and amniotic fluid, increases most steeply in the third trimester. The fat stores your body lays down serve as energy reserves for labor and breastfeeding, not excess weight. Most of these pounds leave your body within the first few weeks postpartum as fluid levels normalize and the placenta, amniotic fluid, and extra blood are no longer needed.
Gaining Too Much or Too Little
Both ends of the spectrum carry real risks, which is why the recommended ranges exist in the first place.
Excessive Gain
Gaining well above the guidelines raises the chance of gestational diabetes, a larger-than-average baby at birth (called macrosomia), and a higher likelihood of needing a cesarean delivery. Babies born unusually large face their own risks during delivery, including shoulder injuries. Excess gain also makes it harder to return to a healthy weight after pregnancy, which affects long-term health.
Inadequate Gain
Gaining too little is equally concerning. Research across two large study groups found that women who gained less than about 0.66 pounds per week (under 0.3 kg/week) during the third trimester had 1.7 to 2.5 times the risk of having a full-term baby with a very low birth weight, under 5.5 pounds. Low gain doesn’t just mean a smaller baby; it’s associated with restricted fetal growth that can affect a newborn’s health in the first days and weeks of life.
If your weight seems to be plateauing or dropping in the third trimester and you’re not yet near your due date, it’s worth bringing up at your next appointment. A temporary dip from a stomach bug is different from consistently low gain over several weeks.
Calorie Needs in the Third Trimester
Supporting this growth doesn’t require eating dramatically more. Most normal-weight pregnant women need about 2,400 calories per day during the third trimester, which works out to roughly 300 extra calories above pre-pregnancy needs. That’s the equivalent of a yogurt with granola and fruit, or a slice of whole-grain toast with avocado and an egg.
The quality of those calories matters more than the number. Your baby is building bone, brain tissue, and fat reserves in the final weeks, so protein, calcium, iron, and omega-3 fatty acids do the heavy lifting. Gaining at a healthy rate doesn’t mean restricting food. It means eating consistently and choosing foods that deliver nutrients rather than empty calories. If you’re gaining faster than expected, small shifts like cutting back on sugary drinks or processed snacks are more effective than skipping meals, which can cause blood sugar swings.
Weight Gain With Twins
If you’re carrying twins, the numbers shift significantly. The CDC recommends a total gain of 37 to 54 pounds for women who started at a normal weight, 31 to 50 pounds for overweight women, and 25 to 42 pounds for obese women. Weekly gain in the third trimester is higher, often over 1.5 pounds per week for normal-weight mothers of twins. Tracking your weight weekly and comparing it to your provider’s target range helps catch deviations early, since twin pregnancies leave less room for error.
Sudden Weight Changes to Watch For
A slow, steady upward trend is normal. What’s not normal is a sudden jump of several pounds in a day or two, especially when paired with swelling in your face or hands. Rapid weight gain from fluid retention can signal preeclampsia, a condition involving dangerously high blood pressure. Mild ankle swelling is common and harmless in the third trimester, but sudden puffiness in the face, tight rings on your fingers, or a sharp spike on the scale warrants a call to your provider.
On the other end, losing 1 to 3 pounds very close to your due date is often a sign that labor is approaching. This small drop comes from shifting fluid levels as your body prepares for delivery, and it’s considered a normal prelabor change rather than a cause for concern.
Week-to-Week Fluctuations Are Normal
Your weight won’t increase in a perfectly smooth line. Water retention, bowel habits, meal timing, and even the time of day you step on the scale can cause swings of 1 to 3 pounds from one check to the next. What matters is the overall trend across weeks, not any single weigh-in. If you’re tracking at home, weighing yourself at the same time of day in similar clothing gives you the most consistent picture. A week where you gain 2 pounds followed by a week where you gain nothing typically averages out to the expected rate and isn’t a reason to worry.