Most women should gain about 1 pound per week during the second trimester, which works out to roughly 12 to 14 pounds over those 13 weeks. The exact target depends on your pre-pregnancy BMI, whether you’re carrying one baby or multiples, and how much you gained in the first trimester. Here’s how to figure out where you should land.
Weekly Targets by BMI
The overall recommended weight gain for your entire pregnancy is based on your BMI before you became pregnant:
- 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
Most of this gain happens during the second and third trimesters. Research shows an average gain of about 1 pound per week during the second trimester, with the observed range running from 0.7 to 1.4 pounds per week depending on the individual. Women with a higher pre-pregnancy BMI should aim for the lower end of that range, while underweight women can expect to gain closer to the higher end.
In practical terms, if you’re a normal-weight woman who gained 3 to 5 pounds in the first trimester, you’d aim for roughly a pound a week through weeks 14 to 27, putting you at about 16 to 18 pounds total by the end of the second trimester. If you’re overweight, your weekly pace might be closer to 0.5 to 0.7 pounds per week during this stretch.
Where the Weight Actually Goes
It can feel strange to gain a pound a week when your baby is still measured in ounces for much of the second trimester. But the weight isn’t all baby. Your body is building an elaborate support system, and much of the second trimester gain goes toward that infrastructure.
By the end of pregnancy, the typical weight breakdown looks like this: the baby accounts for 7 to 8 pounds, the placenta adds about 1.5 pounds, and amniotic fluid contributes another 2 pounds. Your blood volume increases by 3 to 4 pounds, extra fluid adds 2 to 3 pounds, your uterus grows by about 2 pounds, and breast tissue adds 1 to 3 pounds. Fat stores, which your body lays down primarily to fuel breastfeeding, account for 6 to 8 pounds.
The blood volume expansion and fluid increases ramp up significantly during the second trimester, which is a big part of why weight gain accelerates compared to the first trimester.
Twins Change the Numbers
If you’re carrying twins, the overall target is 35 to 45 pounds for the full pregnancy. That translates to roughly 1.5 pounds per week during the second and third trimesters, noticeably more than the singleton target. The higher recommendation reflects the greater demands of growing two babies, two amniotic sacs, and a larger placenta (or two), along with a bigger increase in blood volume.
What Happens if You Gain Too Much
Gaining more than the recommended amount raises the risk of gestational diabetes. In normal-weight women, each meaningful jump above the predicted gain increases the odds of developing gestational diabetes by roughly 24%. The pattern holds for women who start pregnancy at a higher weight as well. Babies born to mothers with gestational diabetes tend to be larger than average, which can complicate delivery and increase the chance of a cesarean section.
Excessive gain also makes it harder to lose the weight after delivery. Women who gain well above the guidelines are more likely to retain that weight a year postpartum, which can raise baseline health risks for future pregnancies.
What Happens if You Gain Too Little
Insufficient weight gain carries its own set of problems. The clearest risk is restricted fetal growth, where the baby doesn’t reach their full growth potential in the womb. Research from a large study in Bangladesh found that inadequate weight gain nearly doubled the odds of a full-term baby being born at low birth weight (under 5.5 pounds). It also increased the odds of the baby being small for gestational age by about 40%.
Too-low gain in the later trimesters has also been linked to a higher risk of preterm birth. If you’re consistently gaining less than half a pound per week in the second trimester and you started at a normal or underweight BMI, it’s worth discussing with your provider.
Calorie Needs in the Second Trimester
You don’t need to eat dramatically more to hit these targets. The second trimester calls for roughly 300 to 350 extra calories per day compared to your pre-pregnancy intake. That’s about the equivalent of a cup of yogurt with fruit and a handful of nuts, or an extra small meal. The first trimester requires little to no extra calories, and the third trimester bumps the need up to about 450 extra calories per day.
Quality matters more than quantity. Protein supports the rapid tissue building happening in the second trimester, and iron needs increase as your blood volume expands. If you’re gaining faster than expected despite eating normally, it’s often fluid retention rather than overeating, especially later in the second trimester when swelling becomes more common.
Week-to-Week Fluctuations Are Normal
Your weight will not increase in a smooth, linear line. You might gain 2 pounds one week and nothing the next. Daily weight can swing by 1 to 3 pounds based on water retention, sodium intake, and bowel habits alone. What matters is the overall trend across weeks, not any single weigh-in.
Your provider should be tracking your weight at every prenatal visit, plotting it against your expected trajectory. If you want to monitor at home, weighing yourself once a week at the same time of day (ideally morning, before eating) gives you the most consistent picture. Checking daily is more likely to cause unnecessary anxiety than provide useful information.
If your gain veers significantly above or below the target for two to three consecutive weeks, that’s a pattern worth bringing up at your next appointment. A single off week is rarely meaningful.