TABLE 4.

Relative risk of spontaneous and indicated preterm birth by body mass index category

PTB category	Entire cohort, N = 443	BMI <25, N = 217	BMI 25–30, N = 96	BMI >30, N = 130
PTB <37 wk	0.66 (0.53–0.81)	0.54 (0.41–0.71)	0.55 (0.36–0.83)	1.55 (0.83–2.89)
Spontaneous PTB <37 wk	0.64 (0.50–0.82)	0.51 (0.37–0.70)	0.63 (0.37–1.07)	1.72 (0.77–3.84)
Indicated PTB <37 wk	0.72 (0.38–1.39)	0.82 (0.27–2.49)	0.33 (0.10–1.10)	1.19 (0.34–4.17)

All entries expressed as relative risk (95% confidence interval).

BMI, body mass index; PTB, preterm birth.