Table 3.

Rates and likelihood ratios (LR) for spontaneous preterm births, iatrogenic preterm births and term births

Notch	N	%	LR (95% CI)
Term births
No notch	3779	90.6	1.15 (1.1‐1.2)
Unilateral	167	78.4	0.40 (0.30‐0.55)
Bilateral	94	68.6	0.25 (0.17‐0.35)
Total	4040	89.4

Spontaneous				Iatrogenic			Total
Notch	N	%	LR (95% CI)	N	%	LR (95% CI)	N	%	LR (95% CI)
Preterm birth <37 wk
No notch	231	5.5	0.95 (0.91‐1.0)	161	3.9	1.5 (1.4‐1.7)	392	14.9	0.9 (0.83‐0.91)
Unilateral	17	8	1.6 (1.0‐2.6)	29	13.6	3.6 (2.5‐5.2)	46	21.6	2.5 (1.8‐3.4)
Bilateral	11	8	1.9 (1.0‐3.5)	32	23.4	6.8 (4.7‐9.9)	43	40	4.1 (2.9‐5.8)
Total	259	5.7		222	4.9		481	10.6
Preterm birth <34 wk
No notch	93	2.2	1.0 (0.97‐1.1)	51	1.2	0.62 (0.52‐0.74)	144	3.4	0.83 (0.77‐0.90)
Unilateral	2	0.9	0.46 (0.12‐1.8)	17	8	5.5 (3.5‐8.4)	19	8.9	2.5 (1.6‐4.0)
Bilateral	3	2.2	1.1 (0.37‐3.5)	21	15.3	10.7 (7.1‐16.0)	24	17.5	5.2 (3.5‐7.9)
Total	98	2.2		89	2		187	4.2
Preterm birth <32 wk
No notch	1	0.5	1.02 (0.96‐1.09)	35	0.8	0.61 (0.49‐0.76)	36	1.1	0.81 (0.73‐0.90)
Unilateral	2	1.5	0.38 (0.05‐2.6)	12	5.6	5.5 (3.3‐9.1)	14	7.1	2.7 (1.6‐4.5)
Bilateral	56	1.3	1.2 (0.31‐4.8)	15	10.9	10.5 (6.6‐16.6)	71	12.2	5.5 (3.4‐8.8)
Total	59	1.3		62	1.4		121	2.7