Most women should gain about 1 pound per week during the third trimester, which works out to roughly 11 to 13 pounds over the final three months of pregnancy. That rate varies based on your pre-pregnancy BMI, and the range is wider than many people expect. Here’s what the numbers actually look like and where all that weight goes.
Weekly Rate by BMI Category
The third trimester is when weight gain accelerates the most. Your baby is growing rapidly, your blood volume is still expanding, and your body is storing energy for labor and breastfeeding. The recommended weekly pace during this stretch depends on your BMI before pregnancy:
- Underweight (BMI under 18.5): about 1 to 1.3 pounds per week
- Normal weight (BMI 18.5 to 24.9): about 1 pound per week
- Overweight (BMI 25 to 29.9): about half a pound per week
- Obese (BMI 30 or higher): about half a pound per week
These weekly rates apply throughout the second and third trimesters. Because most women gain only 1 to 4 pounds during the first trimester, the bulk of total pregnancy weight arrives in the last two trimesters, with the third trimester accounting for a large share.
Total Weight Gain Targets
To figure out whether your third trimester gain is on track, it helps to know the full-pregnancy targets. The CDC’s current guidelines for a single baby break down like this:
- Underweight: 28 to 40 pounds total
- Normal weight: 25 to 35 pounds total
- Overweight: 15 to 25 pounds total
- Obese: 11 to 20 pounds total
If you’re carrying twins and started at a normal weight, the target jumps to 37 to 54 pounds for the entire pregnancy. Twin pregnancies typically require a faster rate of gain in the third trimester to support two growing babies.
Where the Weight Actually Goes
One reason third trimester gain feels so dramatic is that nearly everything is getting bigger at once. By delivery, a typical breakdown looks like this: the baby accounts for about 7.5 pounds, the placenta adds 1.5 pounds, and amniotic fluid contributes around 2 pounds. That’s only about 11 pounds combined.
The rest is your body doing its job. Your blood volume alone increases by roughly 4 pounds to keep the placenta supplied with oxygen and nutrients. Breast tissue grows, your uterus expands, and your body stores some fat as a fuel reserve for postpartum recovery and milk production. This is why gaining 25 to 35 pounds for a 7- or 8-pound baby makes biological sense.
What Happens if You Gain Too Little
Falling significantly below the recommended range carries real risks. A large meta-analysis published in The BMJ, drawing on data from 1.6 million women, found that gaining below guidelines was linked to a 63% higher likelihood of preterm birth and a 49% higher chance of delivering a baby that was small for gestational age. The risk of low birth weight nearly doubled, and there was also a modest increase in respiratory distress for the newborn.
These risks held across all BMI categories. Even women who started pregnancy at a higher weight saw worse outcomes when they gained too little. Restrictive eating or intentional dieting in the third trimester is not the time to try to minimize the number on the scale.
What Happens if You Gain Too Much
Gaining well above the guidelines carries a different set of concerns. Excess weight gain is associated with larger-than-average babies, which increases the chance of a difficult delivery or cesarean section. It can also make it harder to lose weight after pregnancy, and some research ties excessive gain to a higher risk of gestational diabetes and high blood pressure during pregnancy.
That said, a week or two of faster gain doesn’t necessarily mean you’re off track. Fluid retention is extremely common in the third trimester, and a sudden jump on the scale often reflects water, not fat. Weight can fluctuate by several pounds in a single day depending on hydration, sodium intake, and how much swelling you’re experiencing.
Calorie Needs in the Third Trimester
The caloric cost of the third trimester is smaller than most people assume. You need roughly 2,400 calories per day if you were at a normal weight before pregnancy, which works out to about 300 extra calories beyond what you’d eat when not pregnant. That’s roughly the equivalent of a cup of yogurt with some fruit and granola, or a small sandwich.
Quality matters more than quantity at this stage. Your baby’s brain is developing rapidly, bones are hardening, and iron demands are at their peak. Protein, iron-rich foods, calcium, and omega-3 fats do more for healthy weight gain than simply eating more of whatever is available. If you’re gaining faster than expected, the fix is usually adjusting the types of food rather than cutting portions drastically.
When Weight Gain Patterns Shift Suddenly
Steady, gradual gain is the pattern to aim for. A sudden spike of several pounds in a week, especially if it comes with swelling in your face or hands, headaches, or vision changes, can signal preeclampsia rather than normal weight gain. That’s a situation worth calling your provider about promptly.
On the other end, some women notice their weight plateaus or even dips slightly in the final week or two before labor. This is common and usually reflects a shift in fluid balance as your body prepares for delivery. A short stall at 38 or 39 weeks is very different from chronically low gain throughout the trimester.
Your provider will track your weight at every prenatal visit during the third trimester. If your trajectory is consistently above or below the expected curve, they can help you adjust your eating plan or investigate whether something else is going on. The goal isn’t to hit a perfect number every single week. It’s to stay within a reasonable range over the full 12 to 13 weeks of the trimester.