Most women gain about 1 pound per week during the third trimester, though the exact target depends on your pre-pregnancy BMI. Over the final 13 weeks of pregnancy, that adds up to roughly 8 to 14 pounds for most women, making the third trimester the period of fastest weight gain in the entire pregnancy.
Weekly Targets by Pre-Pregnancy BMI
The Institute of Medicine guidelines, endorsed by the American College of Obstetricians and Gynecologists, break recommended weight gain into categories based on your BMI before you became pregnant. These weekly rates apply to both the second and third trimesters, since most weight gain in the first trimester is minimal (typically 1 to 4 pounds total).
- Underweight (BMI below 18.5): About 1 to 1.3 pounds per week, with a total pregnancy goal 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 goal of 25 to 35 pounds.
- Overweight (BMI 25 to 29.9): About 0.5 to 0.7 pounds per week, with a total pregnancy goal of 15 to 25 pounds.
- Obese (BMI 30 or higher): About 0.4 to 0.6 pounds per week, with a total pregnancy goal of 11 to 20 pounds.
These are averages, not precision targets. Your weight will fluctuate day to day based on fluid retention, meals, and how recently you used the bathroom. What matters is the overall trend across weeks, not the number on any single morning.
Where the Weight Actually Goes
The third trimester is when your baby does most of its growing, going from about 2 pounds at week 28 to a typical birth weight of 7 to 8 pounds. But the baby only accounts for part of what the scale shows. Here’s the approximate breakdown of total pregnancy weight gain:
- Baby: 7 to 8 pounds
- Placenta: 1.5 pounds
- Amniotic fluid: 2 pounds
- Increased blood volume: 3 to 4 pounds
- Breast tissue growth: 1 to 3 pounds
- Uterine growth: 2 pounds
- Maternal fat stores: 6 to 8 pounds
The fat stores serve a biological purpose: they’re fuel reserves your body builds for labor, postpartum recovery, and breastfeeding. Much of this fat is deposited earlier in pregnancy, so what you’re gaining in the third trimester is largely baby, fluid, and blood volume. That’s why the scale can jump noticeably in the final weeks even if your eating habits haven’t changed.
Twin Pregnancies Have Different Targets
If you’re carrying twins, the guidelines are substantially higher. A total gain of 35 to 45 pounds is consistent with healthy full-term twin delivery, which works out to about 1.5 pounds per week during the second and third trimesters. For women carrying twins who started pregnancy overweight, the total target is typically 31 to 50 pounds, though your provider will tailor this based on how the pregnancy is progressing.
Calorie Needs in the Third Trimester
The third trimester requires the most energy of any stage in pregnancy, but the increase is smaller than many people expect. Most women need about 2,400 calories per day in the third trimester, which is roughly 200 more than the second trimester and about 300 more than their pre-pregnancy intake. That extra 300 calories is roughly a cup of yogurt with fruit and granola, or a handful of nuts with a piece of cheese.
The quality of those calories matters more than hitting an exact number. Your baby is building bone, brain tissue, and fat reserves during these final months, so protein, iron, calcium, and omega-3 fatty acids all play a larger role than they did earlier in pregnancy. If you’re gaining faster than expected, the solution is rarely to restrict food intake. It’s more useful to look at what you’re eating and whether liquid calories, processed snacks, or large portions have crept in.
What Happens if You Gain Too Much
Gaining well above the recommended range is linked to having a larger-than-average baby, which increases the likelihood of a cesarean delivery and can cause complications during vaginal birth. Excessive gain also makes it harder to return to your pre-pregnancy weight afterward. Research consistently shows that women who exceed the guidelines retain significantly more weight at one year postpartum compared to women who stay within range.
Rapid weight gain in the third trimester, particularly more than 2 to 3 pounds in a single week, can also be a sign of fluid retention related to preeclampsia. If the gain is sudden and accompanied by swelling in your face or hands, headaches, or vision changes, that’s worth a same-day call to your provider. Gradual gain that’s simply on the higher end is less urgent but still worth discussing at your next appointment.
What Happens if You Gain Too Little
Inadequate weight gain is associated with lower birth weight and a higher chance of delivering a baby that’s small for gestational age. Babies born underweight face greater risks of feeding difficulties, trouble regulating body temperature, and longer hospital stays. For women with a higher pre-pregnancy BMI, the relationship is more nuanced. Some research suggests that very limited weight gain in obese women may reduce cesarean delivery rates and the chance of having an overly large baby, but it also raises the risk of the baby being too small. It’s a balance that depends heavily on individual circumstances.
Common reasons for low gain in the third trimester include severe heartburn or reflux making meals uncomfortable, the baby pressing on your stomach and reducing appetite, or simply not eating enough protein and calorie-dense foods. Eating smaller, more frequent meals often helps when large meals feel impossible.
Tracking Your Weight at Home
Your provider weighs you at every prenatal visit, which in the third trimester typically means every two weeks and then weekly after 36 weeks. If you want to track at home, weigh yourself no more than once a week, at the same time of day, in similar clothing. Daily weighing tends to cause unnecessary anxiety because normal fluid shifts in late pregnancy can swing the scale by 2 to 4 pounds in a single day.
The pattern you’re looking for is a fairly steady upward trend. A week or two of plateau is normal and not a concern. A sudden spike of several pounds in a few days warrants attention, not because of the weight itself, but because it can signal fluid retention. Similarly, losing weight in the third trimester without trying, or consistently gaining nothing over several weeks, is something to bring up with your provider so they can check that the baby’s growth is on track.