Table 4.

Associations of oral contraceptive pill (OCP) use before pregnancy with asthma in 24,472 children followed to 36 months old.

Timing of OCP use	Type of OCP	N (%)a,c of children with:		Crude OR (95% CI)	Adjustedc OR (95% CI)
		Asthma	No Asthma
	Total	2,155	22,317
Year before pregnancy	No OCPs	1,242 (58)	13,339 (60)	1.00 (referent)	1.00 (referent)
	Combined pills only	754 (35)	7,581 (34)	1.07 (0.97–1.17)	1.05 (0.95–1.17)
	Mini-pills only	130 (6)	1,190 (5)	1.17 (0.97–1.42)	1.00 (0.81–1.23)
4 months before pregnancy	No OCPs	1,659 (77)	17,286 (78)	1.00 (referent)	1.00 (referent)
	Combined pills only	399 (19)	4,150 (19)	1.00 (0.89–1.12)	1.03 (0.91–1.16)
	Mini-pills only	71 (3)	641 (3)	1.15 (0.90–1.48)	1.01 (0.76–1.33)

^aNumber and percentage of children correspond to the crude models. Analyses included 24,472 children in crude models and 22,201 children in adjusted models.

^bPercentages were calculated using the total number of cases or controls as the denominator. The small category of children whose mothers reported using both combined pills and mini-pills in the year before pregnancy is not shown. For OCP use in the four months before pregnancy, data is missing for a small proportion of the children.

^cEstimates were adjusted for maternal history of asthma and atopy (neither, asthma only, atopy only, both), maternal age (<25, 25–30, >30 years), smoking during first trimester of pregnancy (yes/no), folate supplementation during first trimester of pregnancy (yes/no), number of previous live births (0,1,>1), pre-pregnancy body mass index (<18.5, 18.5–24.9, 25.0–29.9, >29.9), maternal education (<13, 13–16, >16 years), maternal income (<150,000, 150,000–299,000, >299,000 Nkr), child’s sex, child’s gestational age (<37, 37–38, 39–41, >41 weeks), parental smoking in the first 3 months after birth (yes/no), breastfeeding at 6 months (yes/no), season of birth (Mar-May, Jun-Aug, Sep-Nov, Dec-Feb), and year of birth.