Weight gain is perhaps the biggest side effect of being pregnant…aside from getting a baby out of the deal. But whether you started your pregnancy overweight or are simply packing on the pounds now that you’re with child, pregnancy is never a good time to attempt weight loss.

When carrying a baby, your body is growing and feeding another life. Any restrictions you place on yourself are also being placed on the fetus. So, when you fail to get enough calories and nutrients, you put your baby at risk.

“The amount of weight gained during pregnancy can affect the immediate and future health of a woman and her infant,” explains Dr. Soha Elgharib, OB/GYN at Torrance Memorial Medical Center in Los Angeles.

“While evidence supports associations between excessive gestational weight gain and increased birth weight and postpartum weight retention, it also supports associations between inadequate weight gain and decreased birth weight,” she says.

In other words, if you don’t gain the proper amount of weight during pregnancy, your child could be born underweight.

What Is “Normal” Weight Gain?

According to the American Congress of Obstetricians and Gynecologists (ACOG), it is ideal for a woman to have a body mass index between 18.5 and 24.9 at the start of her pregnancy, and to gain between 25 and 35 pounds over the course of it.

If you begin pregnancy underweight, ACOG recommends a weight gain of up to 40 pounds. Women who are overweight at the start of a pregnancy, with a BMI between 25 and 29.9, should only gain 15 to 26 pounds.

Only a small portion of the weight gained during pregnancy is attributed to the weight of the fetus itself. Much of it includes the weight of additional fluids such as increased blood volume, fat stores, and amniotic fluid, which protects the baby.

Extra Nutrients Important to a Growing Baby

When you try to restrict calories to limit weight gain or even lose weight while pregnant, your fetus isn’t getting the nutrients it needs to grow and develop. Iron, calcium, and folate are some of the critical nutrients needed during pregnancy. Iron is needed for cell growth and calcium helps form your baby’s teeth and bones. Adequate folate prevents spina bifida — when the baby’s spinal cord fails to develop properly — and neural tube defects. A lack of folate has been linked to low birth weight and premature delivery.

The Takeaway

Trying to stay within ACOG’s recommended ranges of weight gain is the healthiest option for both you and your baby. This doesn’t mean dieting, but controlling weight gain by practicing healthy habits.

Elgharib suggests that pregnant women maintain a reasonable exercise program throughout pregnancy. This could include:

  • brisk walking
  • swimming
  • group fitness classes specifically for pregnant women

After childbirth, you’ll have plenty of opportunities to get back into shape. For now, nurturing your body and that of your child with healthy foods and moderate activity should be a priority.