MONDAY, Sept. 21, 2009 (HealthDay News) -- Along with keeping mom healthy, regular exercise during pregnancy helps prevent excessive newborn weight, a new study shows.
Published in the October issue of Obstetrics and Gynecology, the Norwegian researchers found that the odds of delivering a too-big baby dropped by as much as 28 percent in women who exercised regularly in their second and third trimesters during their first pregnancy.
"Women often adopt healthier habits before and during pregnancy, like stopping caffeine use. This study suggests that adding exercise to that list may be icing on the cake," said Dr. Robert Welch, chairman of obstetrics and gynecology at Providence Hospital in Southfield, Mich.
Known medically as fetal macrosomia, a heavier birth weight poses a risk to both the baby and the mother. If a baby weighs more than 8.8 pounds, the risk of delivery problems, C-sections, postpartum hemorrhage and low Apgar scores all increase, according to background information in the study. Larger birth weights have also been associated with an increased risk of obesity later in life, according to the researchers.
The study also reported that the number of too-big babies appears to be on the rise, while the number of women exercising during pregnancy is on the decline.
To measure what effect regular exercise has on newborn weight, the Norwegian researchers reviewed data from the Norwegian Mother and Child Cohort study. That database included information on nearly 37,000 women, whose pregnancies lasted at least 37 weeks.
All of the women were pregnant with one child. Two-thirds of the women were normal weight, and 20 percent were overweight, but not obese.
Exercise information was gathered at weeks 17 and 30 of the pregnancies. In women who'd never been pregnant before, 43 percent said they exercised three times a week or more before pregnancy. In women who'd previously been pregnant, 32 percent said they exercised three times a week or more.
By the 30th week of pregnancy, 25 percent reported never exercising, and 19 percent said they exercised one to three times a month. Twenty-nine percent reported exercising one to two times weekly, while 24 percent said they were exercising three or more times each week.
Pre-pregnancy exercise didn't seem to make a difference in a baby's birth weight, but exercise during pregnancy did. In women who'd never been pregnant before, those who were exercising at least three times a week had a 28 percent reduced risk of a large birth weight baby, while those who were still regularly exercising at 30 weeks had a 23 percent decreased risk of having a too-big baby.
The effects of exercise didn't appear to be as consistently beneficial in women who'd already had children. When these women danced or participated in low-impact aerobics, they also reduced the likelihood of delivering a large baby, but when they swam or trained in fitness centers, the benefit disappeared.
Although the study wasn't able to address why this was so, Dr. Steven Allen, chairman of obstetrics and gynecology at Scott & White Healthcare in Temple, Texas, said it may be that this may be a risk factor that's less modifiable in subsequent pregnancies, or "they may not have had enough exercise."
Allen said that while exercise during pregnancy is definitely a good idea, these findings might be different if done with a different population. For example, American women are likely more ethnically diverse and have different average body-mass index levels.
But, in any case, Allen said, "Exercise should be encouraged for everyone who's healthy enough to do it. Exercise shouldn't be discontinued just because you're pregnant."
Allen added that research in the United States has also shown that women who exercise are less likely to have preterm deliveries.
Welch cautioned that as women progress in pregnancy, they should avoid any exercise that has them lay flat on their back, because this can restrict blood flow to both baby and mom. Also, contact sports are out, as is anything where falling might be likely, such as horseback riding.
He said he tells his patients to keep their heart rate to no more than 120 beats per minute during exercise. This allows you to get an aerobic workout, but isn't so much that it might shunt blood away from the baby, Welch explained.
Read more advice about exercise during pregnancy from the March of Dimes.