Table 3.
Associations of oral contraceptive pill (OCP) use before pregnancy with wheezing in 42,520 children followed to 18 months old.
| N (%) a,c of children with: |
||||||
|---|---|---|---|---|---|---|
| Wheezing | Timing of OCP use |
Type of OCP | Wheezing | No Wheezing | Crude OR (95% CI) |
Adjustedc OR (95% CI) |
| Total | 5,356 | 36,535 | ||||
| 6–8 months |
Year before pregnancy |
No OCPs | 3,321 (62) | 21,897 (60) | 1.00 (referent) | 1.00 (referent) |
| Combined pills only | 1,584 (306) | 12,377 (34) | 0.84 (0.79–0.90) | 0.97 (0.90–1.04) | ||
| Mini-pills only | 388 (7) | 1,920 (5) | 1.33 (1.19–1.50) | 1.19 (1.05–1.34) | ||
| 4 months before pregnancy |
No OCPs | 4,219 (79) | 28,415 (78) | 1.00 (referent) | 1.00 (referent) | |
| Combined pills only | 860 (16) | 6,685 (18) | 0.87 (0.80–0.94) | 0.98 (0.90–1.06) | ||
| Mini-pills only | 206 (4) | 1,021 (3) | 1.36 (1.17–1.59) | 1.18 (1.01–1.39) | ||
| Total | 7,634 | 34,257 | ||||
| 9–11 months |
Year before pregnancy |
No OCPs | 4,630 (61) | 20,588 (60) | 1.00 (referent) | 1.00 (referent) |
| Combined pills only | 2,408 (32) | 11,553 (34) | 0.93 (0.88–0.98) | 1.02 (0.96–1.09) | ||
| Mini-pills only | 497 (7) | 1,811 (5) | 1.22 (1.10–1.35) | 1.11 (0.99–1.24) | ||
| 4 months before pregnancy |
No OCPs | 5,945 (78) | 26,689 (78) | 1.00 (referent) | 1.00 (referent) | |
| Combined pills only | 1,304 (17) | 6,241 (18) | 0.94 (0.88–1.00) | 1.01 (0.94–1.09) | ||
| Mini-pills only | 281 (4) | 946 (3) | 1.33 (1.16–1.53) | 1.18 (1.02–1.37) | ||
| Total | 9,576 | 32,315 | ||||
| 12–14 months |
Year before pregnancy |
No OCPs | 5,715 (60) | 19,503 (60) | 1.00 (referent) | 1.00 (referent) |
| Combined pill only | 3,181 (33) | 10,780 (33) | 1.01 (0.96–1.06) | 1.06 (1.00–1.12) | ||
| Mini-pill only | 573 (6) | 1,735 (5) | 1.13 (1.02–1.24) | 1.10 (0.99–1.22) | ||
| 4 months before pregnancy |
No OCPs | 7,475 (78) | 25,159 (78) | 1.00 (referent) | 1.00 (referent) | |
| Combined pills only | 1,684 (18) | 5,861 (18) | 0.97 (0.91–1.03) | 1.03 (0.96–1.10) | ||
| Mini-pills only | 306 (3) | 921 (3) | 1.12 (0.98–1.28) | 1.10 (0.96–1.27) | ||
| Total | 8,930 | 32,961 | ||||
| 15–18 months |
Year before pregnancy |
No OCPs | 5,302 (59) | 19,916 (60) | 1.00 (referent) | 1.00 (referent) |
| Combined pills only | 3,033 (34) | 10,928 (33) | 1.04 (0.99–1.10) | 1.02 (0.97–1.08) | ||
| Mini-pills only | 490 (6) | 1,818 (6) | 1.01 (0.91–1.12) | 0.99 (0.88–1.11) | ||
| 4 months before pregnancy |
No OCPs | 6,943 (78) | 25,691 (78) | 1.00 (referent) | 1.00 (referent) | |
| Combined pills only | 1,610 (18) | 5,935 (18) | 1.00 (0.94–1.07) | 0.99 (0.93–1.06) | ||
| Mini-pills only | 264 (3) | 963 (3) | 1.01 (0.88–1.17) | 1.02 (0.88–1.18) | ||
Number and percentage of children correspond to the crude models. There were 42,520 children followed to 18 months with data for lower respiratory tract infections or wheezing from 6 to 18 months. For wheezing, analyses included 41,891 children in crude models and 38,037 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.