Table 2.
Adjusted relative risk (RRs) and predicted absolute risks (ARs) of pregnancy complications according to interpregnancy interval (IPI) stratified by pregnancy complication at first pregnancy for mothers with their first two consecutive births during the study period (n=252 368 mothers)
| Interpregnancy interval (months): RR, AR and RD (95% CI) | ||||||||
| Outcome | 3 | 6 | 12 | 18 | 24 | 36 | 48 | 60 |
| Preeclampsia (PE) | ||||||||
| Previous PE | ||||||||
| RR (95% CI) | 1.09 (0.94 to 1.25) | 0.99 (0.89 to 1.09) | 0.93 (0.85 to 1.03) | 1 (Reference) | 0.97 (0.90 to 1.05) | 1.04 (0.95 to 1.13) | 1.06 (0.98 to 1.16) | 1.06 (0.98 to 1.15) |
| AR % (95% CI) | 16.3 (13.8 to 18.9) | 14.7 (12.9 to 16.4) | 13.8 (12.3 to 15.3) | 14.8 (13.2 to 16.4) | 14.4 (12.9 to 15.9) | 15.5 (14.0 to 17.0) | 16.0 (14.3 to 17.6) | 15.9 (14.3 to 17.6) |
| RD % (95% CI) | 1.5 (−1.00.6 to 4.1) | −0.1 (−1.7 to 1.5) | −1.0 (−2.5 to 0.4) | Reference | −0.4 (−1.6 to 0.8) | 0.7 (−0.7 to 2.1) | 1.2 (−0.3 to 2.6) | 1.1 (−0.4 to 2.6) |
| No previous PE | ||||||||
| RR (95% CI) | 1.24 (1.07 to 1.43) | 1.00 (0.90 to 1.11) | 0.90 (0.81 to 0.99) | 1 (Reference) | 1.04 (0.96 to 1.13) | 1.23 (1.13 to 1.35) | 1.34 (1.23 to 1.46) | 1.40 (1.29 to 1.53) |
| AR % (95% CI) | 1.5 (1.3 to 1.8) | 1.1 (1.0 to 1.3) | 1.0 (0.9 to 1.1) | 1.1 (1.0 to 1.2) | 1.1 (1.0 to 1.2) | 1.4 (1.3 to 1.5) | 1.6 (1.4 to 1.8) | 1.7 (1.5 to 1.9) |
| RD % (95% CI) | 0.4 (0.2 to 0.7) | 0.1 (−0.1 to 0.2) | −0.1 (−0.2 to 0.01) | Reference | 0.1 (−0.0 to 0.1) | 0.3 (0.2 to 0.4) | 0.5 (0.4 to 0.6) | 0.6 (0.5 to 0.8) |
| Gestational diabetes | ||||||||
| Previous GDM | ||||||||
| RR (95% CI) | 1.11 (0.95 to 1.29) | 0.87 (0.78 to 0.97) | 0.94 (0.85 to 1.04) | 1 (Reference) | 0.96 (0.88 to 1.04) | 1.07 (0.98 to 1.18) | 1.14 (1.05 to 1.25) | 1.18 (1.07 to 1.29) |
| AR % (95% CI) | 39.7 (30.1 to 49.2) | 30.3 (23.5 to 37.1) | 32.6 (24.5 to 40.7) | 35.3 (28.0 to 42.6) | 33.3 (25.4 to 41.2) | 38.6 (31.8 to 45.5) | 41.5 (35.1 to 47.8) | 43.2 (38.3 to 48.2) |
| RD % (95% CI) | 4.4 (−2.6 to 11.3) | −5.0 (−9.0 to −0.9) | −2.7 (−6.7 to 1.3) | Reference | −2.0 (−5.4 to 1.4) | 3.3 (−0.5 to 7.2) | 6.2 (1.9 to 10.5) | 7.9 (2.1 to 13.9) |
| No previous GDM | ||||||||
| RR (95% CI) | 1.00 (0.85 to 1.16) | 0.87 (0.78 to 0.97) | 0.87 (0.79 to 0.96) | 1 (Reference) | 1.20 (1.11 to 1.29) | 1.75 (1.62 to 1.90) | 2.18 (2.01 to 2.35) | 2.58 (2.38 to 2.79) |
| AR % (95% CI) | 3.0 (2.5 to 3.4) | 2.4 (2.2 to 2.7) | 2.3 (2.1 to 2.6) | 2.7 (2.4 to 2.9) | 3.2 (3.0 to 3.5) | 4.9 (4.5 to 5.2) | 6.3 (5.8 to 6.8) | 7.6 (7.0 to 8.3) |
| RD % (95% CI) | 0.3 (−0.2 to 0.8) | −0.2 (−0.5 to 0.1) | −0.3 (−0.6 to −0.1) | Reference | 0.5 (0.4 to 0.9) | 2.2 (1.9 to 2.5) | 3.6 (3.2 to 4.1) | 4.90 (4.4 to 5.6) |
IPI was modelled using restricted cubic splines with knots placed at 3, 6, 12, 18, 24, 36, 48 months of IPI. Models were adjusted for maternal age, socioeconomic status (SES), birth year, ethnicity, marital status at birth prior to IPI and partner change at recent birth with 18 months of IPI as reference. Maternal age was modelled using restricted cubic splines with 4 knots at the 5th, 35th, 65th and 95th percentiles (ages 18, 24, 29 and 35); predicted absolute risks are reported at representative values of covariates: Caucasian, married, average SES, average maternal age (25.1) and birth year in 2010 at birth prior to the IPI.
GDM, gestational diabetes; RD, risk difference.