Regular Exercise During Pregnancy May Lower Risk for Excessive Birth Weight

From Medscape Medical News CME
Laurie Barclay, Désirée Lie,
Obstet Gynecol. 2009;114:770-776.

Clinical Context

Macrosomia, defined as birth weight of 4000 or 4500 g regardless of birth length, has increased in frequency in the past decades and is associated with increased perinatal and neonatal morbidity and mortality rates. Although exercise has been shown to be beneficial in pregnancy, the frequency and intensity of exercise decrease as pregnancy progresses.

This is a prospective cohort study of pregnant women in Norway to examine the association between self-reported exercise before and during pregnancy and the risk for excessive newborn birth weight.


Study Highlights

The data were derived from the Norwegian Mother and Child Cohort Study, a nationwide cohort linked to the Medical Birth Registry of Norway.
Included were women from 50 of 52 maternity units in Norway who received a routine ultrasound examination at 17 weeks, delivered at 37 weeks of gestation or later, and who completed 3 questionnaires during pregnancy, 2 at 17 weeks, and 1 at 30 weeks of gestation.
Excluded were women with multiple pregnancies or with unknown birth dates of their infants.
1 questionnaire administered at 17 weeks asked about lifestyle, including exercise before and during pregnancy, and the other was a food frequency questionnaire.
The third questionnaire administered at 30 weeks focused on maternal outcomes during pregnancy and followed up on some items from the first questionnaire.
For all exercises, women were asked about type and frequency of exercise, with degree of frequency from "never" to "three or more times a week."
For prepregnancy exercise, women were asked at week 17 for their frequency and type of exercise 3 months before the current pregnancy.
Primary outcome was excessive birth weight, defined as equal or above the 90th percentile (4170 g for nulliparous women and 4362 g for multiparous women).

There were 16,064 nulliparous and 20,805 multiparous women.
Mean energy intake was 9600 kcal daily, mean total gestational weight gain was 9300 g, and two thirds of women had a normal prepregnancy body mass index.
At week 17, a total of 10% were smokers.
Mean birth weight was 3683 g, and 10.9% of infants had excessive birth weight.
A greater number of infants with excessive birth weight were born to multiparous vs nulliparous women.
Nulliparous and multiparous women did not differ in age, smoking, height, diabetes, or education, but nulliparous women were younger, had lower energy intake, and gained more weight.
The highest proportion of overweight women, nonexercisers, and excessive newborn weight was found in the multiparous group.
Regular exercise performed 3 months before the current pregnancy did not decrease the risk for high newborn birth weight in nulliparous or multiparous women.
Nulliparous women who reported exercising 3 times or more weekly in week 17 were less likely to have a newborn with excessive birth weight (P for trend = .008); this was not affected by adjustment for diabetes and preeclampsia.
Nulliparous women who reported exercising 1 to 2 times weekly in week 30 were also at lower risk of having a newborn with excessive birth weight.
Walking (aOR, 0.86) and running (aOR, 0.63) in nulliparous women in week 17 and walking in week 30 (aOR, 0.84) were negatively associated with excessive newborn weight.
Multiparous women who participated in dancing in week 17 were less likely to deliver an infant with excessive weight (aOR, 0.75).
Low-impact aerobics (aOR, 0.68) and dancing (aOR, 0.69) at week 30 were associated with a lower risk for excessive newborn birth weight in multiparous women.
However, weight training in fitness centers in week 17 and swimming in week 30 in multiparous women were associated with a higher risk for excessive birth weight.
The authors concluded that exercise during pregnancy, but not before pregnancy, was associated with a lower risk for excessive newborn birth weight; they suggested that this benefit may be the result of the effect of exercise on glucose tolerance.

Clinical Implications

Self-reported exercise before pregnancy is not associated with a lower risk for excessive newborn birth weight in nulliparous or multiparous women.

Self-reported exercise during pregnancy is associated with a lower risk for excessive newborn birth weight in nulliparous and multiparous women.