Most people gain about 1 pound per week during the second trimester, putting total second-trimester weight gain somewhere around 12 to 14 pounds. That said, the healthy range is wider than many people expect, and your starting weight, whether you’re carrying multiples, and your individual metabolism all shift the target.
Week-by-Week Rate of Gain
The second trimester spans weeks 13 through 27, and weight gain picks up noticeably compared to the first trimester, when many people gain only 2 to 4 pounds total. Studies show an average gain of about 0.45 kg (1 pound) per week during the second trimester, though the normal range runs from roughly 0.3 to 0.7 kg (0.7 to 1.5 pounds) per week. Early in the trimester, around weeks 13 to 20, gain tends to be on the lower end. From weeks 20 to 30 it picks up, averaging 0.7 to 1.4 pounds per week.
If you gained very little in the first trimester due to nausea, you may see a faster ramp-up now. If you gained more than expected early on, your weekly rate may be slightly lower. Neither pattern is unusual.
What the Guidelines Recommend by Pre-Pregnancy BMI
The total amount of weight you should gain across pregnancy depends on your BMI before you became pregnant. These are the Institute of Medicine targets for total pregnancy weight gain:
- 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
Roughly half of total pregnancy weight gain happens during the second trimester, since the third trimester rate is slightly lower (closer to 0.9 pounds per week on average). So for a normal-weight person aiming for 25 to 35 pounds overall, roughly 12 to 16 of those pounds will arrive between weeks 13 and 27.
Where the Weight Actually Goes
It can feel like the number on the scale is climbing fast, but very little of the second-trimester gain is body fat. For a full pregnancy weight gain of about 27.5 pounds (12.5 kg), the weight at term breaks down roughly like this: the baby accounts for about 5.3 pounds, the placenta about 1.2 pounds, amniotic fluid about 1.7 pounds, the uterus about 1.8 pounds, breast tissue about 0.7 pounds, and increased blood volume about 2.8 pounds. Extra fluid in your tissues adds another 3 to 10 pounds depending on whether you experience swelling.
Altogether, the products of conception (baby, placenta, and amniotic fluid) make up about 35 percent of total weight gain. The rest is your body building the infrastructure to support the pregnancy: more blood, larger fluid reserves, and energy stores for breastfeeding. During the second trimester specifically, your blood volume is expanding rapidly and the baby is growing from under an ounce at week 13 to nearly 2 pounds by week 27.
Calorie Needs in the Second Trimester
Supporting this growth doesn’t require eating dramatically more. The recommended increase during the second trimester is about 300 to 400 extra calories per day compared to your pre-pregnancy intake, bringing the typical daily target to around 2,200 calories. For context, that’s roughly a snack-sized addition: a Greek yogurt with fruit, a handful of nuts and a piece of cheese, or a peanut butter sandwich. The first trimester requires almost no caloric increase, and the third trimester bumps the target to roughly 2,400 calories per day.
Quality matters more than quantity. Your body needs more iron, folate, calcium, and protein during this period. Protein needs rise to about 71 grams per day, and iron demands nearly double because of the expanding blood supply.
If You’re Carrying Twins
Weight gain targets are significantly higher for twin pregnancies. The recommended total gain is 35 to 45 pounds, with a weekly target of about 1.5 pounds per week during the second and third trimesters. That puts second-trimester gain for a twin pregnancy closer to 20 to 22 pounds. If you’re carrying multiples and gaining less than a pound a week during this period, it’s worth discussing with your provider.
Risks of Gaining Too Much or Too Little
Gaining well above the guidelines increases your risk of gestational diabetes, which can cause the baby to grow larger than normal and complicate delivery. Excessive gain also raises the likelihood of preeclampsia, a condition marked by high blood pressure that can become serious if untreated. After delivery, excess weight gained during pregnancy is harder to lose and is linked to higher long-term obesity risk.
Gaining too little carries its own problems. Insufficient weight gain in the second trimester is associated with smaller babies and, in some cases, preterm birth. The baby’s most rapid organ development and bone growth happen during this period, so consistent, steady gain matters.
A few weeks of faster or slower gain are normal. Weight gain during pregnancy rarely follows a perfectly smooth line. Water retention, meal timing, and even the time of day you step on the scale can swing the number by a pound or two. The overall trend across weeks is more meaningful than any single weigh-in.