Most women gain about 1 pound per week during the third trimester, putting total third-trimester weight gain somewhere between 8 and 15 pounds depending on pre-pregnancy BMI. This is the fastest period of weight gain in pregnancy, driven largely by rapid fetal growth and increases in blood volume, amniotic fluid, and maternal fat stores.
Where the Weight Actually Goes
The third trimester is when the bulk of pregnancy weight piles on because everything is growing at once. Your baby alone gains roughly 176 grams (about 6 ounces) per week from around 24 weeks onward, arriving at a typical birth weight of 7 to 8 pounds. But the baby is only part of the picture. The total weight gained across pregnancy breaks down roughly like this:
- Baby: 7 to 8 pounds
- Fat stores: 6 to 8 pounds
- Increased blood volume: 3 to 4 pounds
- Amniotic fluid: 2 pounds
- Placenta: 1.5 pounds
Much of the blood volume expansion, amniotic fluid increase, and fetal growth happens in the final 12 weeks. That’s why the scale moves faster in the third trimester than it did earlier, even if your eating habits haven’t changed much. Fat stores also continue building during this period, providing energy reserves your body will draw on during labor and breastfeeding.
Recommended Gain Based on Your Starting Weight
The total recommended weight gain for your entire pregnancy, set by the Institute of Medicine and endorsed by ACOG, depends on your pre-pregnancy BMI. The third trimester typically accounts for about a third to nearly half of the total, since the first trimester contributes relatively little (often just 1 to 5 pounds).
- 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
If you’re carrying twins and started at a normal weight, the total target jumps to 37 to 54 pounds. Overweight women carrying twins are guided toward 31 to 50 pounds, and obese women toward 25 to 42 pounds. Twin pregnancies tend to deliver earlier, so the third trimester may be shorter, but weekly gains are higher because two babies are growing simultaneously.
Calorie Needs in the Third Trimester
Supporting this growth doesn’t require eating dramatically more. Most women need about 2,400 calories per day during the third trimester, which works out to roughly 300 extra calories beyond what you’d normally eat. That’s the equivalent of a handful of nuts with a piece of fruit, or a slice of whole-grain toast with peanut butter. The modest increase surprises many people, but most of the weight gain is driven by biological processes (expanding blood supply, growing a placenta) rather than by calories consumed.
When Weight Gain Happens Too Fast
A pound a week is typical. Gaining significantly more than that over a sustained period raises the odds of complications. Women who gain above the recommended range have a notably higher risk of cesarean delivery, particularly those who started pregnancy at a normal or underweight BMI. Excess gain also makes it harder to return to your pre-pregnancy weight. In a large Danish study of nearly 61,000 women, those who gained 44 pounds or more during pregnancy were 6.2 times more likely to retain at least 11 extra pounds six months after delivery compared to women who stayed within guidelines. About 25 percent of women who gained that much moved up an entire BMI category and stayed there at least six months postpartum.
There’s also a difference between gradual excess gain and sudden spikes. Gaining more than 3 to 5 pounds in a single week can signal preeclampsia, a serious blood pressure condition. That kind of rapid gain is usually caused by fluid retention rather than fat. Damaged blood vessels leak fluid into surrounding tissue, causing visible swelling in the hands, face, and feet. If you notice puffiness that comes on quickly alongside a sharp jump on the scale, that warrants immediate medical attention.
When Weight Gain Is Too Low
Gaining less than recommended carries its own risks. Inadequate weight gain is associated with premature birth and low birth weight, defined as a baby weighing less than 5.5 pounds at delivery. It can also mean your body isn’t building the fat stores it needs for labor, recovery, and milk production. Some women gain less in certain weeks due to appetite changes, heartburn, or simply running out of room in their abdomen as the baby grows. Occasional slow weeks are normal. A persistent pattern of little or no gain over several weeks is what raises concern.
What Normal Fluctuations Look Like
Day-to-day weight in the third trimester can swing by 2 to 4 pounds based on water retention alone. Your blood volume is at its peak, your kidneys are processing more fluid, and hormonal shifts cause your body to hold onto water unpredictably. Eating a salty meal, standing for long periods, or even changes in weather can affect how much fluid you retain on any given day.
Because of this, weekly averages matter more than daily weigh-ins. If you’re tracking at home, weighing yourself at the same time of day, wearing similar clothing, gives the most consistent picture. The overall trend across weeks is what matters, not what happens between Monday and Tuesday. A steady upward slope of about a pound per week, give or take, is exactly what healthy third-trimester weight gain looks like.