Background
Methods
Study population
Preterm delivery
Outcome variables
Covariates
Statistical analysis
Results
No preterm delivery, n (%) N = 1,780,798 (91.6) | Preterm delivery, n (%) N = 162,918 (8.4) | |
---|---|---|
Age in years | ||
< 20 | 97,007 (5.5) | 14,384 (8.8) |
20–29 | 1,151,931 (64.7) | 104,337 (64.0) |
30–39 | 507,226 (28.5) | 41,921 (25.7) |
≥ 40 | 24,634 (1.4) | 2276 (1.4) |
Native country | ||
Sweden | 1,509,135 (84.7) | 138,441 (85.0) |
Elsewhere | 271,663 (15.3) | 24,477 (15.0) |
Education level | ||
Less than upper secondary | 233,341 (13.1) | 24,540 (15.1) |
Upper secondary | 800,419 (45.0) | 77,826 (47.8) |
Third level | 709,299 (39.8) | 57,702 (35.4) |
Missing | 37,739 (2.1) | 2850 (1.8) |
Body mass index in early pregnancy (kg/m2) | ||
Underweight, < 18.5 | 41,129 (2.3) | 4830 (3.0) |
Normal, 18.5–24.9 | 655,619 (36.8) | 55,415 (34.0) |
Overweight, 25–29.9 | 178,593 (10.0) | 15,447 (9.5) |
Obese, ≥ 30 | 64,011 (3.6) | 6445 (4.0) |
Missing | 841,446 (47.3) | 80,781 (49.6) |
Maternal smoking | ||
No | 950,672 (53.4) | 83,138 (51.0) |
Yes | 187,197 (10.5) | 21,404 (13.1) |
Missing | 642,929 (36.1) | 58,376 (35.8) |
Gestational diabetes (ever) | ||
No | 1,764,968 (99.1) | 160,133 (98.3) |
Yes | 15,830 (0.9) | 2785 (1.7) |
Preeclampsia (ever) | ||
No | 1,709,392 (96.0) | 141,702 (87.0) |
Yes | 71,406 (4.0) | 21,216 (13.0) |
Small for gestational age (SGA) (ever) | ||
No | 1,700,028 (95.6) | 140,572 (86.5) |
Yes | 77,671 (4.4) | 22,008 (13.5) |
Decade of first birth | ||
1973–1979 | 478,412 (26.9) | 39,063 (24.0) |
1980–1989 | 385,271 (21.6) | 42,506 (26.1) |
1990–1999 | 386,441 (21.7) | 38,576 (23.7) |
2000–2012 | 530,674 (29.8) | 42,773 (26.3) |
Parity | ||
1 | 610,494 (34.3) | 38,564 (23.7) |
2 | 793,672 (44.6) | 70,936 (43.5) |
3 | 291,217 (16.4) | 35,819 (22.0) |
4 | 64,811 (3.6) | 11,970 (7.4) |
5 or more | 20,604 (1.2) | 5629 (3.5) |
History of any preterm or early term delivery
Chronic kidney disease (N = 18,001) | |||
---|---|---|---|
n | Minimally adjusted | Fully adjusted | |
HR (95% CI) | HR (95% CI) | ||
Exposure 1 | |||
Term delivery (≥ 37 weeks) | 15,914 | 1.0 | 1.0 |
Preterm delivery (< 37 weeks) | 2087 | 1.47 (1.40–1.53) | 1.39 (1.32–1.45) |
Exposure 2 | |||
Term delivery (≥ 37 weeks) | 15,914 | 1.0 | 1.0 |
Moderate preterm delivery (32–36 + 6 weeks) | 1733 | 1.41 (1.34–1.48) | 1.35 (1.28–1.41) |
Very preterm delivery (28–31 + 6 weeks) | 244 | 1.77 (1.56–2.01) | 1.55 (1.36–1.76) |
Extremely preterm delivery (< 28 weeks) | 110 | 2.05 (1.70–2.48) | 1.84 (1.52–2.22) |
Exposure 3 | |||
Full term delivery (39–41 + 6 weeks) | 9134 | 1.0 | 1.0 |
Post-term delivery (≥ 42 weeks) | 2237 | 0.94 (0.90–0.98) | 1.04 (0.99–1.09) |
Early term delivery (37–38 + 6 weeks) | 4543 | 1.13 (1.09–1.17) | 1.19 (1.15–1.24) |
Moderate preterm delivery (32–36 + 6 weeks) | 1733 | 1.44 (1.37–1.52) | 1.43 (1.36–1.51) |
Very preterm delivery (28–31 + 6 weeks) | 244 | 1.81 (1.60–2.06) | 1.65 (1.45–1.87) |
Extremely preterm delivery (< 28 weeks) | 110 | 2.11 (1.75–2.54) | 1.96 (1.63–2.37) |
Exposure 4 | |||
Term delivery (≥ 37 weeks) | 15,914 | 1.0 | 1.0 |
Spontaneous preterm delivery (< 37 weeks) | 1571 | 1.32 (1.25–1.39) | 1.32 (1.25–1.39) |
Iatrogenic preterm delivery—preeclampsia (< 37 weeks) | 230 | 2.82 (2.48–3.21) | 2.81 (2.46–3.20) |
Iatrogenic preterm delivery—SGA (< 37 weeks) | 182 | 1.74 (1.50–2.00) | 1.66 (1.44–1.93) |
Iatrogenic preterm delivery—preeclampsia and SGA (< 37 weeks) | 104 | 2.11 (1.74–2.56) | 2.10 (1.73–2.55) |
Exposure 5 | |||
Two term deliveries (≥ 37 weeks) | 6013 | 1.0 | 1.0 |
One preterm (< 37 weeks) and one term delivery (≥ 37 weeks) | 723 | 1.51 (1.40–1.63) | 1.34 (1.24–1.45) |
Two preterm deliveries (< 37 weeks) | 93 | 1.67 (1.36–2.05) | 1.46 (1.19–1.79) |
End-stage kidney disease (N = 1268) | |||
---|---|---|---|
n | Minimally adjusted | Fully adjusted | |
HR (95% CI) | HR (95% CI) | ||
Exposure 1 | |||
Term delivery (≥ 37 weeks) | 1051 | 1.0 | 1.0 |
Preterm delivery (< 37 weeks) | 217 | 2.56 (2.21–2.97) | 2.22 (1.90–2.58) |
Exposure 2 | |||
Term delivery (≥ 37 weeks) | 1051 | 1.0 | 1.0 |
Moderate preterm delivery (32–36 + 6 weeks) | 174 | 2.36 (2.01–2.78) | 2.08 (1.76–2.45) |
Very preterm delivery (28–31 + 6 weeks) | 30 | 3.81 (2.67–5.45) | 2.90 (2.02–4.16) |
Extremely preterm delivery (< 28 weeks) | 13 | 4.15 (2.35–7.33) | 3.61 (2.03–6.39) |
Exposure 3 | |||
Full term delivery (39–41 + 6 weeks) | 584 | 1.0 | 1.0 |
Post-term delivery (≥ 42 weeks) | 146 | 0.97 (0.81–1.16) | 1.13 (0.94–1.36) |
Early term delivery (37–38 + 6 weeks) | 321 | 1.44 (1.26–1.66) | 1.50 (1.31–1.73) |
Moderate preterm delivery (32–36 + 6 weeks) | 174 | 2.61 (2.20–3.10) | 2.40 (2.02–2.86) |
Very preterm delivery (28–31 + 6 weeks) | 30 | 4.22 (2.94–6.05) | 3.37 (2.34–4.87) |
Extremely preterm delivery (< 28 weeks) | 13 | 4.60 (2.60–8.16) | 4.21 (2.37–7.49) |
Exposure 4 | |||
Term delivery (≥ 37 weeks) | 1051 | 1.0 | 1.0 |
Spontaneous preterm delivery (< 37 weeks) | 142 | 2.01 (1.68–2.39) | 1.99 (1.67–2.38) |
Iatrogenic preterm delivery—preeclampsia (< 37 weeks) | 33 | 7.70 (5.41–10.97) | 6.70 (4.70–9.56) |
Iatrogenic preterm delivery—SGA (< 37 weeks) | 25 | 3.84 (2.58–5.71) | 3.72 (2.49–5.53) |
Iatrogenic preterm delivery—preeclampsia and SGA (< 37 weeks) | 17 | 6.72 (4.15–10.86) | 6.25 (3.86–10.11) |
Exposure 5 | |||
Two term deliveries (≥ 37 weeks) | 350 | 1.0 | 1.0 |
One preterm (< 37 weeks) and one term delivery (≥ 37 weeks) | 75 | 2.71 (2.11–3.48) | 2.12 (1.64–2.74) |
Two preterm deliveries (< 37 weeks) | 8 | 2.61 (1.29–5.26) | 2.02 (1.00–4.08) |
History of spontaneous or iatrogenic preterm delivery
Sensitivity analysis
Chronic kidney disease (N = 10,922) | End-stage kidney disease (N = 547) | |||
---|---|---|---|---|
n | Fully adjusted | n | Fully adjusted | |
HR (95% CI) | HR (95% CI) | |||
Exposure 1 | ||||
Term delivery (≥ 37 weeks) | 9428 | 1.0 | 424 | 1.0 |
Preterm delivery (< 37 weeks) | 1494 | 1.39 (1.32–1.47) | 123 | 2.28 (1.85–2.81) |
Exposure 2 | ||||
Term delivery (≥ 37 weeks) | 9428 | 1.0 | 424 | 1.0 |
Moderate preterm delivery (32–36 + 6 weeks) | 1217 | 1.34 (1.26–1.42) | 92 | 2.03 (1.61–2.56) |
Very preterm delivery (28–31 + 6 weeks) | 182 | 1.59 (1.37–1.84) | 21 | 3.17 (2.01–5.01) |
Extremely preterm delivery (< 28 weeks) | 95 | 2.05 (1.67–2.51) | 10 | 5.14 (2.81–9.40) |
Exposure 3 | ||||
Full term delivery (39–41 + 6 weeks) | 5032 | 1.0 | 213 | 1.0 |
Post-term delivery (≥ 42 weeks) | 1202 | 1.04 (0.97–1.11) | 48 | 1.01 (0.74–1.39) |
Early term delivery (37–38 + 6 weeks) | 3194 | 1.21 (1.15–1.26) | 163 | 1.48 (1.20–1.82) |
Moderate preterm delivery (32–36 + 6 weeks) | 1217 | 1.44 (1.35–1.53) | 92 | 2.36 (1.83–3.04) |
Very preterm delivery (28–31 + 6 weeks) | 182 | 1.71 (1.47–1.98) | 21 | 3.70 (2.32–5.90) |
Extremely preterm delivery (< 28 weeks) | 95 | 2.20 (1.80–2.70) | 10 | 5.98 (3.24–11.03) |
Exposure 4 | ||||
Term delivery (≥ 37 weeks) | 9428 | 1.0 | 424 | 1.0 |
Spontaneous preterm delivery (< 37 weeks) | 1084 | 1.31 (1.23–1.40) | 71 | 1.89 (1.46–2.44) |
Iatrogenic preterm delivery—preeclampsia (< 37 weeks) | 188 | 2.76 (2.39–3.19) | 22 | 6.52 (4.19–10.14) |
Iatrogenic preterm delivery—SGA (< 37 weeks) | 134 | 1.79 (1.51–2.13) | 19 | 4.89 (3.33–8.40) |
Iatrogenic preterm delivery—preeclampsia and SGA (< 37 weeks) | 88 | 2.18 (1.77–2.69) | 11 | 5.91 (3.24–10.76) |
Exposure 5 | ||||
Two term deliveries (≥ 37 weeks) | 4208 | 1.0 | 189 | 1.0 |
One preterm (< 37 weeks) and one term delivery (≥ 37 weeks) | 529 | 1.32 (1.21–1.45) | 37 | 1.70 (1.18–2.44) |
Two preterm deliveries (< 37 weeks) | 72 | 1.43 (1.13–1.81) | 7 | 2.66 (1.24–5.69) |