Effect of Modifiable Risk Factors on Preterm Birth: A Population Based-Cohort.

Objectives The purpose of this study is to evaluate the prevalence, impact, and interaction of short interpregnancy interval (IPI), pre-pregnancy body mass index (BMI) category, and pregnancy weight gain (PWG) on the rate of preterm birth. Methods This is a population-based retrospective cohort study using vital statistics birth records from 2006 to 2011 in OH, US, analyzing singleton live births to multiparous mothers with recorded IPI (n = 393,441). Preterm birth rate at <37 weeks gestational age was compared between the referent pregnancy (defined as normal pre-pregnancy maternal BMI, IPI of 12-24 months, and Institute of Medicine (IOM) recommended PWG) and those with short or long IPI, abnormal BMI (underweight, overweight, and obese), and high or low PWG (under or exceeding IOM recommendations). Results Only 6 % of the women in this study had a referent pregnancy, with a preterm birth rate of 7.6 % for this group. Short IPIs of <6 and 6-12 months were associated with increased rates of preterm birth rate to 12.9 and 10.4 %, respectively. Low PWG compared to IOM recommendations for pre-pregnancy BMI class was also associated with increased preterm birth rate of 13.2 % for all BMI classes combined. However, the highest rate of preterm birth of 25.2 % occurred in underweight women with short IPI and inadequate weight gain with adjOR 3.44 (95 % CI 2.80, 4.23). The fraction of preterm births observed in this cohort that can be attributed to short IPIs is 5.9 %, long IPIs is 8.3 %, inadequate PWG is 7.5 %, and low pre-pregnancy BMI is 2.2 %. Conclusions Our analysis indicates that a significant proportion of preterm births in Ohio are associated with potentially modifiable risk factors. These data suggest public health initiatives focused on preterm birth prevention could include counseling and interventions to optimize preconception health and prenatal nutrition.