Table 3.

Risk of PTB in subsequent birth per interpregnancy interval.

Recurrent PTB		PTB < 24		PTB < 32		PTB < 37
Interpregnancy interval		OR	95 % CI	OR	95 % CI	OR	95 % CI
	0 −3 months	1.5	0.76 - 2.9	2.3	1.4 - 3.7	1.8	1.2 – 2.6
	4 −6 months	1.0	0.45 - 2.2	1.2	0.66 - 2.1	1.3	0.83 – 1.9
	7 −12 months	0.89	0.39 - 2.0	1.0	0.58 - 1.9	0.89	0.57 – 1.4
	13 −36 months	1.0	Ref	1.0	Ref	1.0	Ref
	> 36 months	0.39	0.09 - 1.7	0.89	0.40 – 2.0	0.54	0.28 – 1.1