Most people gain about 1 pound per week during the third trimester, which adds up to roughly 12 to 14 pounds over those final three months. That rate can vary based on your pre-pregnancy weight, how much you’ve already gained, and whether you’re carrying one baby or multiples. The third trimester is when weight gain accelerates the most, driven largely by your baby’s rapid growth and your body’s preparation for delivery.
Recommended Total Gain by Pre-Pregnancy BMI
The guidelines used today were established in 2009 and remain the current standard. They base your total recommended weight gain on your body mass index before pregnancy, not on trimester-by-trimester targets. For a single pregnancy:
- 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 to 29.9): 15 to 25 pounds total
- Obese (BMI 30 or higher): 11 to 20 pounds total
Since most people gain only 2 to 5 pounds during the first trimester and roughly a pound per week in the second, the third trimester typically accounts for about a third to nearly half of the total. If you started at a normal weight and are on track to gain 30 pounds overall, you might expect around 12 of those pounds to appear in the final 13 weeks.
For twin pregnancies, total targets are significantly higher. Normal-weight individuals carrying twins are recommended to gain 37 to 54 pounds, with overweight individuals aiming for 31 to 50 pounds. The weekly rate in the third trimester for multiples often exceeds 1.5 pounds.
Where the Weight Actually Goes
The number on the scale can feel surprising, but most of that third-trimester weight isn’t body fat. Here’s a typical breakdown of pregnancy weight gain by the time you deliver:
- Baby: 7 to 8 pounds
- Placenta: 1.5 pounds
- Amniotic fluid: 2 pounds
- Uterus growth: 2 pounds
- Increased blood volume: 3 to 4 pounds
- Extra body fluid: 2 to 3 pounds
- Breast tissue: 1 to 3 pounds
- Fat stores: 6 to 8 pounds
Your baby alone gains roughly 5 pounds during the third trimester, going from around 2 pounds at week 28 to 7 or 8 pounds at birth. That single factor explains a huge chunk of what you see on the scale. Blood volume, fluid retention, and the growing placenta account for much of the rest. The fat stores your body builds serve as energy reserves for labor and breastfeeding.
Why the Scale Jumps Around
Don’t be alarmed if your weight fluctuates by 2 or 3 pounds from one day to the next during the third trimester. Fluid retention increases significantly in the final weeks. Your body carries an extra 5 to 7 pounds of blood and fluid by the end of pregnancy, and how much you notice on any given day depends on salt intake, how long you’ve been on your feet, the temperature, and even the time of day you step on the scale.
Some weeks you may gain 2 pounds, other weeks nothing. The overall trend matters more than any single weigh-in. Your provider will track the pattern across appointments rather than reacting to one number.
Risks of Gaining Too Much
Gaining well above the recommended range in the third trimester is linked to having a larger-than-average baby, which increases the likelihood of a cesarean delivery. Excessive gain also makes it harder to return to your pre-pregnancy weight afterward. Postpartum weight retention is one of the strongest predictors of long-term weight gain, so the pounds added beyond what your body needs don’t simply disappear after birth.
The third trimester requires only about 300 extra calories per day compared to your pre-pregnancy intake, bringing most people to roughly 2,400 calories daily. That’s less than many people assume. It’s the equivalent of a peanut butter sandwich or a cup of yogurt with fruit, not eating for two in any literal sense.
Risks of Gaining Too Little
Insufficient weight gain in the third trimester carries its own concerns. Research from a large study in Bangladesh found that inadequate third-trimester gain nearly doubled the odds of having a baby born at low birth weight and significantly increased the risk of the baby being small for gestational age. Other research has linked poor third-trimester gain to a higher risk of preterm birth.
If you’re struggling to gain weight because of nausea, loss of appetite, or food aversions that have persisted into the third trimester, it’s worth flagging with your provider. Small, frequent, calorie-dense meals often help more than trying to force larger ones.
When a Sudden Jump Is a Warning Sign
A steady pound-per-week pattern is normal. A sudden gain of more than 3 to 5 pounds in a single week is not. That kind of rapid increase, especially if it comes with swelling in the face or hands, headaches, or vision changes, can be a sign of preeclampsia, a serious blood pressure condition that develops in the second half of pregnancy. Preeclampsia causes the body to retain fluid rapidly, which shows up as dramatic, overnight weight gain rather than the gradual climb you’d expect. If you notice this pattern, contact your provider promptly rather than waiting for your next scheduled appointment.