Table 5.

Crude and adjusted odds ratios (95% confidence intervals) of low birth weight in ovarian stimulation and IVF/ICSI groups of women, compared with natural conception group

	Observed effect		Overall effect*		Direct effect†
Group	Odds ratio	P value	Odds ratio	P value	Odds ratio	P value
Natural conception (n=2915)	Reference	-	Reference	-	Reference	-
Ovarian stimulation (n=710)	1.20 (1.04 to 1.38)	0.01	1.07 (0.93 to 1.24)	0.4	1.26 (1.08 to 1.50)	0.002
IVF/ICSI (n=743)	1.26 (1.10 to 1.45)	<0.001	1.09 (0.93 to 1.28)	0.3	1.28 (1.09 to 1.47)	0.004
Subfertility treatment‡ (n=1453)	1.23 (1.10 to 1.37)	<0.001	1.08 (0.96 to 1.22)	0.2	1.27 (1.11 to 1.45)	<0.001

ICSI=intracytoplasmic sperm injection; IVF=in vitro fertilisation.

^*Multivariable analysis accounting for birth year, maternal age, and parity (confounders).

^†Multivariable analysis accounting for birth year, maternal age, and parity (confounders) and for infant sex, caesarean delivery, zygosity, and chorionicity (mediating variables).

^‡Comprises ovarian stimulation and IVF/ICSI groups.