Associations between health behaviours, fertility and reproductive outcomes: triangulation of evidence in the Norwegian Mother, Father and Child Cohort Study (MoBa)

Wootton, Robyn E.; Lawn, Rebecca B.; Magnus, Maria C.; Treur, Jorien L.; Corfield, Elizabeth C.; Njølstad, Pål R.; Andreassen, Ole A.; Lawlor, Deborah A.; Munafò, Marcus R.; Håberg, Siri E.; Davey Smith, George; Reichborn-Kjennerud, Ted; Magnus, Per; Havdahl, Alexandra

doi:10.1186/s12916-023-02831-9

Table 2 Summary level Mendelian randomisation results for health behaviours on age at first birth, number of children and number of miscarriages

From: Associations between health behaviours, fertility and reproductive outcomes: triangulation of evidence in the Norwegian Mother, Father and Child Cohort Study (MoBa)

Exposure	Outcome	Method	N SNP	Beta (95% CI)	P
Drinks per week	Age at first birth	IVW	94	− 0.055 (− 0.145, 0.034)	0.22
		MR Egger	94	0.04 (− 0.095, 0.175)	0.56
		Weighted median	94	− 0.048 (− 0.139, 0.042)	0.30
		Weighted mode	94	− 0.046 (− 0.129, 0.038)	0.29
	Number of children	IVW	83	0.027 (− 0.057, 0.110)	0.53
		MR Egger (SIMEX)	83	0.014 (− 0.029, 0.058)	0.52
		Weighted median	83	− 0.010 (− 0.094, 0.074)	0.82
		Weighted mode	83	0.009 (− 0.068, 0.086)	0.82
	Number of miscarriages	IVW	94	− 0.029 (− 0.097, 0.038)	0.39
		MR Egger	94	− 0.018 (− 0.121, 0.084)	0.73
		Weighted median	94	0.001 (− 0.099, 0.102)	0.98
		Weighted mode	94	0.01 (− 0.084, 0.103)	0.84
Caffeine	Age at first birth	IVW	6	− 0.036 (− 0.13, 0.057)	0.45
		Weighted median	6	0.013 (− 0.073, 0.099)	0.77
		Weighted mode	6	0.033 (− 0.067, 0.134)	0.54
	Number of children	IVW	6	0.021 (− 0.031, 0.073)	0.43
		Weighted median	6	0.021 (− 0.047, 0.089)	0.54
	Number of miscarriages	IVW	6	− 0.042 (− 0.106, 0.022)	0.20
		Weighted median	6	− 0.052 (− 0.128, 0.025)	0.19
		Weighted mode	6	− 0.076 (− 0.178, 0.025)	0.20
Smoking initiation	Age at First Birth	IVW	322	− 0.661 (− 0.757, − 0.566)	3.57 × 10⁻⁴²
		Weighted median	322	− 0.504 (− 0.603, − 0.405)	2.71 × 10⁻²³
		Weighted mode	322	− 0.555 (− 0.785, − 0.326)	3.30 × 10⁻⁶
	Number of children	IVW	323	0.280 (0.205, 0.355)	3.17 × 10⁻¹³
		Weighted median	323	0.207 (0.125, 0.289)	7.11 × 10⁻⁰⁷
		Weighted mode	323	0.177 (− 0.009, 0.363)	0.06
	Number of miscarriages	IVW	322	− 0.123 (− 0.182, − 0.064)	4.68 × 10⁻⁵
		Weighted median	322	− 0.106 (− 0.196, − 0.017)	0.019
		Weighted mode	322	− 0.176 (− 0.399, 0.047)	0.124
BMI	Age at first birth	IVW	95	− 0.108 (− 0.16, − 0.056)	4.32 × 10⁻⁰⁵
		MR Egger	95	− 0.076 (− 0.225, 0.072)	0.32
		Weighted median	95	− 0.043 (− 0.101, 0.015)	0.14
		Weighted mode	95	0.006 (− 0.114, 0.126)	0.92
	Number of children	IVW	91	− 0.014 (− 0.054, 0.027)	0.51
		MR Egger	91	− 0.002 (− 0.117, 0.113)	0.98
		Weighted median	91	− 0.008 (− 0.054, 0.038)	0.73
		Weighted mode	91	− 0.013 (− 0.094, 0.069)	0.76
	Number of miscarriages	IVW	95	0.004 (− 0.033, 0.041)	0.83
		MR Egger	95	0.021 (− 0.086, 0.128)	0.70
		Weighted median	95	0.019 (− 0.033, 0.072)	0.47
		Weighted mode	95	0.013 (− 0.091, 0.116)	0.81

IVW, inverse-variance weighted; BMI, body mass index. The I²_GX suggested that the smoking initiation and caffeine genetic instruments were not suitable for conducting MR Egger (Additional file 1: Table S21). Unweighted SIMEX corrections were conducted for smoking initiation. Age at first birth and number of miscarriages are in females only. Number of children is in males and females combined

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