Table 2.
Associations of oral contraceptive pill (OCP) use before pregnancy with lower respiratory tract infections in 60,225 children followed to 6 months old and 42,520 children followed to 18 months old.
| N (%)a,c of children with: |
||||||
|---|---|---|---|---|---|---|
| Lower respiratory tract infections |
Timing of OCP use |
Type of OCP | Lower respiratory tract infections |
No lower respiratory tract infections |
Crude OR (95% CI) |
Adjustedc OR (95% CI) |
| Total | 3,021 | 57,204 | ||||
| <6 months | Year before pregnancy |
No OCPs | 1,927 (64) | 34,621 (61) | 1.00 (referent) | 1.00 (referent) |
| Combined pills only | 808 (27) | 18,978 (33) | 0.77 (0.70–0.83) | 1.03 (0.94–1.13) | ||
| Mini-pills only | 240 (8) | 3,046 (5) | 1.42 (1.23–1.63) | 1.10 (0.95–1.28) | ||
| 4 months before pregnancy |
No OCPs | 2,417 (80) | 44,685 (78) | 1.00 (referent) | 1.00 (referent) | |
| Combined pills only | 441 (15) | 10,230 (18) | 0.80 (0.72–0.88) | 1.07 (0.96–1.20) | ||
| Mini-pills only | 121 (4) | 1,600 (3) | 1.40 (1.16–1.69) | 1.09 (0.89–1.34) | ||
| Total | 2,863 | 38,515 | ||||
| 6–11 months | Year before pregnancy |
No OCPs | 1,765 (62) | 23,134 (60) | 1.00 (referent) | 1.00 (referent) |
| Combined pills only | 866 (30) | 12,934 (34) | 0.88 (0.81–0.96) | 1.00 (0.91–1.09) | ||
| Mini-pills only | 194 (7) | 2,083 (5) | 1.22 (1.05–1.43) | 1.05 (0.89–1.24) | ||
| 4 months before pregnancy |
No OCPs | 2,271 (79) | 29,961 (78) | 1.00 (referent) | 1.00 (referent) | |
| Combined pills only | 457 (16) | 6,988 (18) | 0.86 (0.78–0.96) | 0.95 (0.85–1.07) | ||
| Mini-pills only | 99 (4) | 1,121 (3) | 1.17 (0.95–1.44) | 0.95 (0.76–1.19) | ||
| Total | 3,480 | 38,063 | ||||
| 12–18 months | Year before pregnancy |
No OCPs | 2,058 (59) | 22,919 (60) | 1.00 (referent) | 1.00 (referent) |
| Combined pills only | 1,180 (34) | 12,700 (33) | 1.04 (0.96–1.12) | 1.03 (0.95–1.12) | ||
| Mini-pills only | 199 (6) | 2,083 (6) | 1.06 (0.91–1.24) | 1.07 (0.91–1.26) | ||
| 4 months before pregnancy |
No OCPs | 2,712 (78) | 29,643 (78) | 1.00 (referent) | 1.00 (referent) | |
| Combined pills only | 632 (18) | 6,855 (18) | 1.01 (0.92–1.10) | 1.00 (0.91–1.11) | ||
| Mini-pills only | 99 (3) | 1,123 (3) | 0.96 (0.78–1.19) | 0.98 (0.79–1.22) | ||
Number and percentage of children correspond to the crude models. For lower respiratory tract infections at <6 months, analyses included 60,225 children in crude models and 54,234 children in adjusted models. Analyses for lower respiratory tract infections at 6–11 months included 41,378 children in crude models and 37,574 children in adjusted models. Analyses for lower respiratory tract infections at 12–18 months included 41,543 children in crude models and 37,737 children in adjusted models.
Percentages 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.
Estimates 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.