Most women worry about gaining too much weight during pregnancy rather than too little. But if you started pregnancy underweight and then find it difficult to eat in early pregnancy due to morning sickness, you may worry about your baby's nutrition. While not gaining enough weight later in pregnancy and being underweight can cause pregnancy complications, you do not need to eat extra calories in the first trimester of pregnancy, when morning sickness is usually most troublesome, for your baby to grow.
Calorie Requirements
If you're underweight at the start of pregnancy, your doctor may recommend that you start gaining weight as early in the pregnancy as possible, even though your baby doesn't yet need the extra calories to grow. During the second trimester, you need 340 additional calories to meet your needs as well as your baby's, advises registered dietitian Dale Ames Kline. During the third trimester, when your baby puts on the most weight, you need an additional 452 calories per day. If you're underweight, aim for a pregnancy weight gain of 28 to 40 lbs.
Folic Acid
While not consuming extra calories in the first trimester isn't harmful for your baby, not getting enough folic acid, a B vitamin, may cause neural-tube defects. Neural-tube defects include spina bifida, which involves an abnormal opening in the baby's spine, and anencephaly, a condition involving a missing portion of the brain. You need at least 400 mcg per day of folic acid in the first three months of pregnancy. If every woman took folic acid before pregnancy and during early pregnancy, the risk of neural-tube defects could drop by 70 percent, according to the March of Dimes. Even if you don't feel like eating much, make sure you get enough folic acid in a supplement in early pregnancy.
Iron
In the second and third trimesters, you need to increase your iron intake to meet your needs and those of your baby's because of your increased blood volume. Iron-deficiency anemia can cause an increased risk of preterm delivery, low birthweight or stillbirth, and this condition may also lead to anemia in your baby during infancy. Iron pills may make you nauseated, so take them in divided doses if possible or ask your doctor if you can skip the iron in the first trimester and start it in the second, when morning sickness subsides. Iron pills containing ferrous fumarate or ferrous gluconate may upset your stomach less than ferrous sulfate pills.
Potential Complications
A British study published in the January 2001 issue of "BJOG," a journal of obstetrics and gynecology, looked at the effects of being underweight in pregnancy. Researchers studied pregnancy records from 38,182 underweight women and found that being underweight in pregnancy was associated with anemia during pregnancy, preterm delivery and low birthweight infants. Underweight women had fewer instances of other pregnancy complications, such as preeclampsia, gestational diabetes and postpartum hemorrhage.
References
- "Today's Dietitian"; Macronutrient Requirements During Pregnancy; Dale Ames Kline, M.S., R.D.; January 2004
- "BJOG"; Is Maternal Underweight Really a Risk Factor for Adverse Pregnancy Outcome? A Population-based Study in London; N.J. Sebire, et al.; January 2001
- BabyCenter; Iron-deficiency Anemia in Pregnancy; December 2009
- March of Dimes; Folic Acid; February 2010
- Palo Alto Medical Foundation: Your First Trimester
