Table 2.

Odds ratios and 95% confidence intervals for PTD as a function of categorized and continuous pre-pregnancy BMI

	Design adjusted only			Fully adjusted
	n a	ORb	95%CI	n	AORb,d	95%CI
BMI
Categorical
Underweight versus Normal	1,042	1.99	0.99–4.01	1,037	2.11	1.03–4.32
Overweight versus Normal		1.08	0.78–1.51		1.07	0.76–1.51
Obese versus Normal		1.42	0.96–2.11		1.31	0.86–2.00
Continuousc
17 versus 24	580	4.02	1.83–8.80	578	4.31	1.94–9.54
19 versus 24		2.70	1.54–4.73		2.84	1.61–5.01
29 versus 24	462	1.39	1.10–1.76	459	1.42	1.10–1.84
34 versus 24		1.95	1.22–3.11		2.01	1.20–3.39

^aHighest and lowest 1% of BMI values excluded

^bAdjusted for frequency matching by race and birth month

^cOdds ratios calculated from beta values of logistic models with a continuous linear BMI term

^dAdjusted for parity, marital status, sleep, and weight gain during prgenancy