Table 2.

Type of delivery and neonatal outcome stratified by mode of conception.

Conceived spontaneously					Conceived by IVF				Adjusted
Outcome	Concord 201 (93.5%)	Discord 14 (6.5%)	RR (95% CI)	P value	Concord 164 (93.2%)	Discord 12 (6.8%)	RR (95% CI)	P value	B-D P value	CMH P value	RR (95% CI)
PTD < 28 wks	4 (2%)	0	0.67 (0.04–11.64)	1.0	5 (3%)	1 (8%)	0.36 (0.05–2.89)	0.35	0.390	0.672	0.65 (0.09–4.87)
PTD < 34 wks	33 (16%)	7 (50%)	0.33 (0.18–0.60)	0.006	23 (14%)	6 (50%)	0.28 (0.14–0.55)	0.005	0.825	<0.001	0.31 (0.19–0.48)
Cesarean section	111 (55%)	10 (72%)	0.77 (0.54–1.10)	0.28	140 (91%)	12 (100%)	0.91 (0.86–0.95)	0.38	0.311	0.078	0.82 (0.70–0.96)
Apgar score 5′ < 7 (either twin)	38 (19%)	7 (50%)	0.38 (0.21–0.69)	0.015	53 (31%)	7 (58%)	0.62 (0.35–1.10)	0.11	0.645	0.001	0.47 (0.31–0.69)
NICU, either twin	39 (19%)	8 (57%)	0.29 (0.18–0.47)	0.003	55 (34%)	8 (67%)	0.50 (0.32–0.79)	0.029	0.693	<0.001	0.42 (0.30–0.59)
Composite end point	72 (35.8%)	11 (78.6%)	2.5 (1.8–3.5)	0.0001	60 (36.5%)	9 (75.0%)	2.0 (1.3–3.0)	0.0002	0.701	<0.001	2.2 (1.6–3.2)

IVF denotes in vitro fertilization; PTD, preterm delivery; NICU, neonatal intensive care unit; RR, relative risk; CI, confidence interval; B-D, Breslow-Day test; CMH, Cochran-Mantel-Haenszel test.