How much weight should I gain during my pregnancy?

Just as there's no such thing as one-size-fits-all maternity wear, there's no such thing as a one-size-fits-all pregnancy weight gain recommendation. Your doctor or midwife will take a number of different factors into account when helping you to come up with a pregnancy "gain plan." Here are the key issues that she will consider when she talks to you about how much weight you should aim to gain over the course of your pregnancy:

• Your pre-pregnancy weight: If you start your pregnancy at a healthy weight, your doctor or midwife will likely encourage you to gain between 25 and 35 pounds during pregnancy—a figure recommended by the National Academy of Sciences/Institute of Medicine (NAS/IOM). If you are underweight, you'll be encouraged to gain a little more—28 to 40 pounds—and if you are overweight, you'll be encouraged to gain a little less—15 to 25 pounds.
• Your age: Because their own bodies are still developing, adolescent women are encouraged to gain more weight than women in their 20s, 30s, and 40s—typically something in the range of 28 to 40 pounds.
• Your height: Short women are often encouraged to gain slightly less than their taller counterparts—typically 18 to 30 pounds.
• The number of babies you are carrying: If you are carrying twins, you will need to gain between 35 and 45 pounds during your pregnancy. If you are carrying triplets or other high-order multiples, you will need to gain even more.

Regardless of your actual weight gain target, you should aim for slow, gradual weight gain during pregnancy. Although you may not gain any weight during the first trimester (and, in fact, you may actually lose a few pounds if you're having particular difficulty with morning sickness), you should aim to gain one pound a week during your second and third trimesters—slightly less if you're overweight, and slightly more if you're underweight. You may not gain any weight during the last four weeks of pregnancy. In fact, you may even lose a pound or two.

This means that you can expect to gain approximately 25 percent of your weight between weeks 12 and 20, another 50 percent between weeks 20 and 30, and the remaining 25 percent between weeks 30 and 36.

By the time you deliver, you will have consumed an extra 80,000 calories—the amount of energy it takes to "grow" a baby.