Risk of primary outcome (preterm birth < 37 weeks’ gestation) and secondary outcomes in association with abnormal prepregnancy serum creatinine (SCr)*
| Outcome† | No. (%) with outcome | Absolute risk difference, % (95% CI) | RR (95% CI) | |
|---|---|---|---|---|
| Unadjusted | Adjusted‡ | |||
| Preterm birth < 37 wk gestation | ||||
| SCr normal: ≤ 95th percentile (n = 52 837) | 3702 (7.0) | 0.0 (ref.) | 1.00 (ref.) | 1.00 (ref.) |
| SCr abnormal: > 95th percentile (n = 2806) | 254 (9.1) | 2.1 (0.96 to 3.10) | 1.28 (1.14 to 1.45) | 1.23 (1.09 to 1.38) |
| Provider-initiated preterm birth < 37 wk gestation | ||||
| SCr normal: ≤ 95th percentile (n = 52 837) | 2097 (4.0) | 0.0 (ref.) | 1.00 (ref.) | 1.00 (ref.) |
| SCr abnormal: > 95th percentile (n = 2806) | 158 (5.6) | 1.7 (0.79 to 2.50) | 1.42 (1.21 to 1.66) | 1.30 (1.11 to 1.52) |
| Spontaneous preterm birth < 37 wk gestation | ||||
| SCr normal: ≤ 95th percentile (n = 52 837) | 1605 (3.0) | 0.0 (ref.) | 1.00 (ref.) | 1.00 (ref.) |
| SCr abnormal: > 95th percentile (n = 2806) | 96 (3.4) | 0.38 (–0.30 to 1.10) | 1.11 (0.90 to 1.36) | 1.12 (0.91 to 1.37) |
| Preterm birth < 32 wk gestation | ||||
| SCr normal: ≤ 95th percentile (n = 52 837) | 491 (0.93) | 0.0 (ref.) | 1.00 (ref.) | 1.00 (ref.) |
| SCr abnormal: > 95th percentile (n = 2806) | 56 (2.0) | 1.1 (0.54 to 1.60) | 2.15 (1.64 to 2.83) | 2.04 (1.54 to 2.69) |
| Preterm birth < 37 wk gestation with severe SGA | ||||
| SCr normal: ≤ 95th percentile (n = 52 781) | 200 (0.38) | 0.0 (ref.) | 1.00 (ref.) | 1.00 (ref.) |
| SCr abnormal: > 95th percentile (n = 2804) | 18 (0.64) | 0.26 (–0.04 to 0.56) | 1.69 (1.05 to 2.74) | 1.52 (0.94 to 2.45) |
| Preterm birth < 37 wk gestation with preeclampsia | ||||
| SCr normal: ≤ 95th percentile (n = 52 837) | 370 (0.70) | 0.0 (ref.) | 1.00 (ref.) | 1.00 (ref.) |
| SCr abnormal: > 95th percentile (n = 2806) | 42 (1.5) | 0.80 (0.34 to 1.30) | 2.14 (1.56 to 2.93) | 1.82 (1.33 to 2.49) |
| Stillbirth at ≥ 20 wk gestation | ||||
| SCr normal: ≤ 95th percentile (n = 53 115) | 278 (0.52) | 0.0 (ref.) | 1.00 (ref.) | 1.00 (ref.) |
| SCr abnormal: > 95th percentile (n = 2831) | 25 (0.88) | 0.36 (0.01 to 0.71) | 1.69 (1.12 to 2.55) | 1.57 (1.04 to 2.37) |
Note: CI = confidence interval, ref. = reference category, RR = relative risk, SCr = serum creatinine, SGA = small for gestational age (birthweight < 5th percentile for gestational age and sex).
↵* Abnormal SCr defined as > 95th percentile (i.e., > 77 μmol/L). The analysis included 55 946 pregnancies from the main cohort with SCr measured within 10 weeks before conception.
↵† For all outcomes except stillbirth, the denominator (n value provided in column 1) is live births. For stillbirths, the denominator is the sum of live births and stillbirths.
↵‡ All models were adjusted for maternal age, rural or urban residence, residential income quintile (Q1 or missing, Q2, Q3, Q4, Q5), world region of origin (Asia, Caribbean/Africa, Hispanic America, other) — each at the time of the index conception — as well as diabetes mellitus, chronic hypertension, and illicit drug or tobacco use within 4 years before the index conception date.