Gaining weight is an important (and inevitable) part of any healthy pregnancy, but how much you gain and when can vary from one new mom to the next. Gaining too much — or too little — can be dangerous for you and the baby.

Overshooting your target weight gain can result in you having a large baby or health complications during delivery, and the more you put on, the more you’ll have to lose to get back to your pre-pregnancy weight. But gaining too little can also put you and your baby risk. Not putting on enough weight during pregnancy can increase the chances of your baby being born early or underweight — both of which can lead to potentially serious consequences. Knowing what range is healthy for you and your baby is key.

Your pre-pregnancy weight is important.

How much your doctor recommends you gain during pregnancy will likely depend on how much you weighed before you were pregnant. A new mom who’s overweight will need to gain less weight than a mom who is a healthy weight, for example. To figure this out, health professionals often use a body mass index (or BMI) to determine whether someone is a healthy weight, underweight, or overweight and then use that to ballpark how much you should aim to gain during pregnancy. Generally speaking, new moms pregnant with only one baby should follow the following guidelines:

  • Underweight (BMI less than 18.5): 28-40 pounds  
  • Normal weight (BMI 18.5-24.9): 25-35 pounds
  • Overweight (BMI 25.0-29.9): 15-25 pounds
  • Obese (BMI greater than 30): 11-20 pounds

It should be noted that BMI isn’t perfect. Someone could be lean and buff yet still clock in as “overweight” on the BMI chart, and a person with a high percentage of body fat might still have a score that says they’re a healthy weight. That’s why it’s so important to talk to your doctor about how much weight gain is right for you during every pregnancy.

Weight gain can vary by type of pregnancy and even by trimester.

It makes sense that women pregnant with multiple birth babies (twins, triplets, etc.) will need to gain more weight than moms of single-birth babies. After all, your body is doing more work growing more babies — and that work takes energy. But it’s not just how many babies are growing — but also the stage they’re in that matters. While a normal weight pregnant woman should try to gain 25-35 pounds during the course of the pregnancy, that weight gain is largely concentrated in the second and third trimesters at a rate of about a pound a week, with little to no weight gain during the first few months of pregnancy.

Weight isn’t everything.

While weight gain is certainly an important factor in pregnancy, other things matter, too, such as eating a well-balanced diet and getting in physical activity. It’s important to talk to your doctor or midwife about any questions or concerns you might have about how much (or little) weight you’re gaining. He or she can help you determine whether you’re on the right track or what strategies you can use to help keep you within your target weight range.