Purpose: To investigate differences in pre-pregnancy BMI status in patients with spontaneous preterm birth (PTB) compared with term birth and assess the role of ethnicity as a risk modifier in BMI-associated PTB.
Methods: A case-control study involving self-reported African American and Caucasian women delivering singletons in Nashville, TN, USA, 2003-2009. Maternal pre-pregnancy BMI was recorded in 447 PTB-cases (African American = 145, Caucasian = 302) and 1315 term-birth controls (African American = 522; Caucasian = 793). Crude and adjusted odds ratio (OR and AOR) for PTB were calculated using normal BMI (18.5-24.9 kg/m(2)) as reference. Age, education, marital status, income, smoking, parity, previous PTB and pregnancy weight gain were included as covariates in logistic regression.
Results: No significant differences were noted in the OR for PTB among different BMI categories when women of different ethnicity were combined. Odds of PTB were greater in obese than in normal weight Caucasian women, even after adjusting for confounders (AOR = 1.84, 95%CI [1.15, 2.95]). Obese African American women had a decreased crude OR for PTB, although this was not significant after adjusting for confounders (AOR = 0.72, 95%CI [0.38, 1.40]). The odds for early PTB (<32 weeks) were decreased in obese compared with normal weight African American women (OR = 0.23, 95%CI [0.08, 0.70]), whereas they were increased in obese compared with normal weight Caucasian women (OR = 2.30, 95%CI [1.32, 4.00]).
Conclusion: The risk for PTB in women with different pre-pregnancy BMI categories differs according to ethnicity.