Table 2.
Hormonal contraceptive use and gestational length at birth by period of last use relative to conception, progestin type, and route of administration
| Preterm birth |
Gestational length (days) |
|||||
|---|---|---|---|---|---|---|
| Exposure | Exposed (n) |
Preterm (n) |
OR (95% CI) | aORa (95% CI) | β (95% CI) unadjusted |
β (95% CI) adjusted* |
| None | 23,421 | 964 | referent | referent | referent | referent |
| 0 - 12 weeks after | ||||||
| Combination OC | 1,062 | 71 | 1.67 (1.30, 2.14) | 1.32 (1.01, 1.73) | −1.19 (−2.08, −0.29) | −0.73 (−1.63, 0.18) |
| Progestin only OC | 359 | 18 | 1.23 (0.76, 1.98) | 1.26 (0.78, 2.04) | −0.52 (−1.75, 0.71) | −0.47 (−1.70, 0.76) |
| Other b | 217 | 5 | 0.55 (0.23, 1.34) | 0.49 (0.20, 1.21) | 1.28 (−0.29, 2.85) | 1.48 (−0.11, 3.06) |
| 1 - >0 months before | ||||||
| Combination OC | 4,660 | 225 | 1.18 (1.02, 1.37) | 1.13 (0.97, 1.31) | 0.11 (−0.30, 0.51) | −0.09 (−0.50, 0.33) |
| Progestin only OC | 1,204 | 30 | 0.60 (0.41, 0.86) | 0.67 (0.46, 0.97) | 0.87 (0.26, 1.48) | 0.66 (0.05, 1.27) |
| Vaginal ring | 356 | 13 | 0.88 (0.51, 1.54) | 0.86 (0.49, 1.51) | 0.18 (−1.06, 1.43) | −0.10 (−1.35, 1.16) |
| Other b | 245 | 7 | 0.69 (0.32, 1.46) | 0.66 (0.31, 1.42) | 0.16 (−1.16, 1.48) | 0.05 (−1.27, 1.36) |
| 4 - >1 month before | ||||||
| Combination OC | 3,833 | 213 | 1.37 (1.18, 1.60) | 1.31 (1.11, 1.53) | −0.49 (−0.93, −0.04) | −0.73 (−1.19, −0.26) |
| Progestin only OC | 1,284 | 53 | 1.00 (0.76, 1.33) | 1.15 (0.87, 1.53) | 0.39 (−0.27, 1.05) | 0.18 (−0.48, 0.85) |
| Vaginal ring | 352 | 12 | 0.82 (0.46, 1.47) | 0.80 (0.45, 1.43) | 0.32 (−0.89, 1.52) | 0.04 (−1.16, 1.25) |
| Other b | 271 | 9 | 0.80 (0.41, 1.56) | 0.76 (0.39, 1.49) | 0.39 (−0.83, 1.61) | 0.30 (−0.93, 1.52) |
| 12 - >4 months before | ||||||
| Combination OC | 4,633 | 241 | 1.28 (1.11, 1.48) | 1.21 (1.04, 1.41) | −0.10 (−0.51, 0.31) | −0.31 (−0.74, 0.11) |
| Progestin only OC | 1,795 | 71 | 0.96 (0.75, 1.23) | 1.10 (0.85, 1.40) | −0.38 (−0.96, 0.19) | −0.56 (−1.14, 0.001) |
| Vaginal ring | 424 | 12 | 0.68 (0.38, 1.21) | 0.68 (0.38, 1.20) | 0.83 (−0.32, 1.98) | 0.54 (−0.63, 1.70) |
| Transdermal | 295 | 10 | 0.82 (0.43, 1.54) | 0.78 (0.41, 1.48) | 1.12 (−0.11, 2.34) | 1.03 (−0.19, 2.25) |
| Injectable | 180 | 14 | 1.96 (1.13, 3.40) | 1.83 (1.06, 3.18) | −1.58 (−3.49, 0.33) | −1.72 (−3.95, 0.50) |
| Other b | 143 | 1 | 0.16 (0.02, 1.17) | 0.18 (0.02, 1.27) | 2.47 (0.99, 3.96) | 2.56 (1.07, 4.05) |
a
adjusted for parity, maternal education, maternal pre-pregnancy BMI, maternal smoking, and maternal age at birth
b
hormonal contraceptive types with <10 exposed cases collapsed into a single “other” category