Obesity in older mothers, gestational weight gain, and risk estimates for preterm phenotypes.

OBJECTIVE

To assess whether advanced maternal age modifies the relationship between maternal pregravid weight status, gestational weight gain patterns, and the occurrence of spontaneous preterm birth (SPB) and medically indicated preterm birth (MIPB).

METHODS

Retrospective cohort analysis of vital statistics data from the state of Florida for the period 2004 through 2007 comprising 311,422 singleton pregnancies (two age groups: 20-24 years old or younger women and >or=35 years or older women). Mothers were classified into five clusters based on their pre-pregnancy body mass index (BMI) values: non-obese (less than 30), class I obese (30.0<or=BMI<or=34.9), class II obese (35.0<or=BMI<or=39.9), class III obese (40<or=BMI<or=49.9), and super-obese (BMI>or=50.0).

RESULTS

MIPB occurred more frequently among older than younger women [11.8% vs. 6.4%, respectively (p<0.0001)) whereas SPB occurred more frequently among younger women [11.3% vs. 10.5%, respectively (p<0.0001)). Maternal obesity increased the risk for MIPB but not for SPB. Regardless of BMI status, the risk of MIPB was elevated among older mothers, particularly among those with suboptimal (<0.23 kg/week) and supraoptimal (>0.68 kg/week) gestational weight gain. A dose-response relationship with increasing gestational weight gain was evident (p<0.01); the greatest risk for MIPB occurred among older mothers with weekly gestational weight gain in excess of 0.79 kg (OR=7.76, 95% CI=5.73-10.5).

CONCLUSION

The occurrence of medically indicated preterm birth is positively associated with increased maternal pregravid body weight, older maternal age and extremes of gestational weight gain. Targeted pre- and inter-conception weight management efforts should be particularly encouraged in older mothers.