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 ≥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 ≤ BMI ≤ 34.9), class II obese (35.0 ≤ BMI ≤ 39.9), class III obese (40 ≤ BMI ≤ 49.9), and super-obese (BMI ≥ 50.0).
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).
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.