Obese or overweight women have a lower risk of delivering prematurely than normal-weight or underweight women. To explore the associations between body weight and the risk of premature delivery, researchers from America followed 253 women, all at a higher-than-normal risk of preterm delivery because of previous preterm births or bleeding problems during the current pregnancy. It was found that those who were overweight or obese had a far lower rate of preterm delivery compared with normal-weight or underweight women. Just over 8 percent gave birth before the 35th week of pregnancy, versus nearly 22 percent of normal-weight or underweight women. Excess weight seemed to lower this risk of delivering prematurely. This could be attributed to the differences in the frequency of uterine contractions because normal-weight and underweight women tend to have more contractions between the 22nd and 34th weeks of pregnancy. The explanation for this finding is not clear, but may have to do with the fact that body fat affects hormone levels, which may in turn affect the frequency of uterine contractions during pregnancy. The findings suggest that when doctors screen women for their risk of preterm birth, overweight women who show uterine-contraction patterns similar to those of thinner women may need to be considered high-risk for early delivery.
Obstetrics & Gynecology
January 2009