Table 6.

Association between maternal history of miscarriages and childhood asthma at 7 years

Study population	Exposure	Exposure group	N	N cases (%)	Unadjusted RR (95% CI)	Adjusted* RR (95% CI)
Register-based cohort	Number of miscarriages within the first 12 gestational weeks	None	374 866	15 628 (4.2)	1	1
		1	73 323	3256 (4.4)	1.07 (1.03 to 1.11)	1.07 (1.03 to 1.11)
		2	18 415	902 (4.9)	1.17 (1.10 to 1.26)	1.18 (1.10 to 1.26)
		3 or more	7798	403 (5.2)	1.24 (1.12 to 1.37)	1.24 (1.12 to 1.37)
	Number of miscarriages between 12 and 23 gestational weeks	None	448 198	18 979 (4.2)	1	1
		1	11 086	546 (4.9)	1.16 (1.07 to 1.27)	1.21 (1.11 to 1.32)
		2	1273	53 (4.2)	0.98 (0.75 to 1.29)	1.04 (0.79 to 1.36)
		3 or more	418	18 (4.3)	1.02 (0.65 to 1.60)	1.04 (0.66 to 1.65)
MoBa	Number of miscarriages within the first 22 gestational weeks	None	60 982	2564 (4.2)	1	1
		1	11 364	499 (4.4)	1.04 (0.95 to 1.15)	1.06 (0.96 to 1.16)
		2	2555	123 (4.8)	1.14 (0.96 to 1.37)	1.18 (0.98 to 1.41)
		3 or more	896	43 (4.8)	1.14 (0.85 to 1.53)	1.14 (0.85 to 1.53)

*The analysis of the register-based cohort was adjusted for maternal age, parity and maternal current asthma. The analysis of MoBa was adjusted for maternal age, parity, education, smoking during pregnancy, prepregnancy BMI and maternal current asthma.

BMI, body mass index; MoBa, Norwegian Mother and Child Cohort Study; RR, relative risk.