Most women gain about 1 pound per week during the third trimester, putting total third-trimester weight gain in the range of 10 to 15 pounds. That makes these final 13 weeks the fastest period of weight gain in pregnancy, driven largely by your baby’s rapid growth, expanding blood volume, and fluid retention. Your starting BMI, whether you’re carrying multiples, and individual physiology all shift that number up or down.
Where the Weight Actually Goes
Third-trimester gain can feel alarming if you’re watching the scale climb a pound or more each week. But very little of it is body fat. Here’s a rough breakdown of where pregnancy weight accumulates across the full nine months:
- Baby: 6.5 to 8.5 pounds at full term
- Fat stores: 6 to 8 pounds
- Increased blood volume: 3 to 4 pounds
- Extra fluid volume: 2 to 3 pounds
- Amniotic fluid: about 2 pounds
- Uterus: about 2 pounds
- Placenta: about 1.5 pounds
- Breast tissue: 1 to 3 pounds
A large share of this accumulates in the third trimester specifically. Your baby roughly triples in weight between week 28 and delivery, gaining an average of about 175 grams (a little over 6 ounces) per week. Fetal growth during these months is essentially linear, meaning the baby puts on a consistent amount each week. At the same time, your blood volume peaks, your body stores additional fluid, and the placenta and amniotic fluid reach their final volumes.
Fluid retention alone can be significant. In women with normal or mild leg swelling, extra fluid outside the bloodstream accounts for roughly 13% of total pregnancy weight gain. Some women retain more than 11 pounds of fluid, which explains why the scale sometimes seems to jump overnight.
Recommended Total Gain by BMI
There are no official third-trimester-only targets. Instead, the CDC provides total pregnancy weight gain recommendations based on your pre-pregnancy BMI, and you can estimate how much of that falls in the final months. Most women gain 2 to 5 pounds total during the first trimester and then roughly a pound per week after that, so third-trimester gain typically represents about a third to nearly half of the total.
- 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
For twins, the numbers are substantially higher. A woman at a normal pre-pregnancy weight carrying twins is advised to gain 37 to 54 pounds total, while an overweight woman with twins should aim for 31 to 50 pounds.
Calorie Needs in the Third Trimester
Your body needs roughly 450 extra calories per day during the third trimester to support fetal growth and the demands of your expanding blood supply. That’s a bit more than the second trimester, which calls for about 340 extra calories daily. To put it in perspective, 450 calories is roughly a peanut butter sandwich with a glass of milk. The gain isn’t about eating for two in any dramatic sense; it’s about consistently adding modest fuel throughout the day.
Risks of Gaining Too Much
Weight gain above recommended ranges raises the risk of pregnancy-related high blood pressure, including preeclampsia and eclampsia. It is also strongly associated with a higher chance of cesarean delivery and with having a large-for-gestational-age baby, which can lead to complications during delivery such as shoulder dystocia.
The effects extend beyond delivery. Women who gain above guidelines tend to retain more weight in the postpartum period, and that retention often carries into subsequent pregnancies. Over time this can shift you into a higher BMI category, increasing your long-term risk for type 2 diabetes and cardiovascular disease.
Risks of Gaining Too Little
Gaining below guidelines carries its own concerns. Inadequate weight gain is linked to delivering a smaller baby and to preterm birth. It’s also moderately associated with difficulty initiating breastfeeding after delivery. If you’re struggling to gain, your provider will likely look at your nutrition, nausea management, and overall calorie intake to find practical ways to close the gap.
When Sudden Gain Is a Warning Sign
Steady, gradual gain is normal. A sudden spike is not. Gaining more than 3 to 5 pounds in a single week may be an early sign of preeclampsia, a serious condition involving high blood pressure and potential organ damage. This type of rapid gain is usually caused by sudden fluid retention rather than fat, and it often comes with other symptoms like severe headaches, vision changes, or swelling in the face and hands. If you notice a sharp, unexpected jump on the scale, contact your provider promptly.
What Comes Off After Delivery
About 11 to 13 pounds typically drop immediately with delivery. That accounts for the baby, the placenta, amniotic fluid, and some blood and fluid loss. Over the following few weeks, another 4 to 5 pounds generally come off as your body sheds retained fluid and your uterus contracts back toward its original size. So within a month of delivery, most women have lost roughly 15 to 18 pounds without any active effort. The remaining weight, mostly fat stores and residual fluid, comes off more gradually over the months that follow.