Table 4.

Statistical analysis of BW

	HFEA-ONS cohort BW coefficient (95% CI)		HFEA-ONS-HES subcohort BW coefficient (95% CI)
	ART (N=75 348)—NCP (N=1 64 823) *adjusted for maternal age at delivery and sex	sART (N=15 875)—NCS (N=14 763) *adjusted for maternal age at delivery, sex and order of pregnancy	HES-ART (N=63 877)— HES-NCP (N=1 27 544) *adjusted for maternal age at delivery, sex, IMD at earliest appointment and ethnicity	HES-sART (N=12 329)— HES-NCS (N=11 343) *adjusted for maternal age at delivery, sex and order of pregnancy
Fresh vs NC (g)	−131 (−140 to 123)	−54 (−72 to 36)	−152 (−162 to 142)	−57 (−75 to –38)
Frozen vs NC (g)	35 (19 to 52)	138 (101 to 175)	3 (−17 to 22)	152 (113 to 190)
Fresh vs frozen (g)	−167 (−183 to 150)	−193 (−232 to 154)	−155 (−175 to 135)	−209 (−249 to –168)

ART, assisted reproductive technology; BW, birth weight; HES, Hospital Episode Statistics; HFEA, Human Fertilisation and Embryology Authority; IMD, Index of Multiple Deprivation; NC, naturally conceived; NCP, Naturally conceived population control; NCS, Naturally conceived siblings; ONS, Office for National Statistics; sART, ART with siblings.