Although preterm birth (PTB) is known to have an effect on renal development, data on the relationship are sparse. A recent study in BMJ examined how PTB affects the risk of chronic kidney disease (CKD) from childhood through middle age.
Using the Swedish birth registry, authors conducted a national cohort study of more than 4 million Swedes born between 1973 and 2014. The researchers organized births into six categories based on delivery, ranging from extremely preterm (22-27 weeks) to post-term (≥ 42 weeks). The study cohort was followed up from the earliest diagnosis of CKD after birth to December 31, 2015 (maximum age = 43 years). CKD was identified using ICD codes from all primary and secondary diagnoses in Swedish hospital and outpatient registries.
In addition to gestational age at birth, the authors looked at other perinatal and maternal characteristics. These included birth year, sex, birth order, and congenital anomalies, as well as maternal age, education level, body mass index (BMI), smoking status, preeclampsia, hypertensive disorders during pregnancy, and diabetes.
The study found that preterm infants were more likely than full-term infants to be male or first-born or to have congenital anomalies and their mothers were more likely to smoke, have lower education, higher BMI, and be at extremes of age.
Overall, 4,305 (0.1%) participants were diagnosed with CKD during 87.0 million person-years of follow-up (incidence rate = 4.95 per 100,000 person-years). Incidence rates for CKD by gestational age were 9.24 for preterm infants, 5.90 for infants with early-term deliveries, and 4.47 for those with full-term deliveries.
Across the entire range (0-43 years), gestational age at birth was inversely associated with risk of CKD (adjusted hazard ratio for each additional age at gestation, 0.92, 95% CI 0.90-0.93; P< 0.001). PTB and early-term birth were associated with nearly two-fold and 1.3-fold higher risks of CKD, respectively, compared with full-term birth. Participants born extremely preterm had a three-fold higher risk of CKD.
When examining narrower age intervals, PTB was significantly associated with increased risk of CKD in early childhood (ages 0-9 years: 5.09, 95% CI 4.11 – 6.31, P< 0.001). This association weakened in later adolescence but remained significant.
The authors believe their findings support the association between CKD and PTB seen in earlier studies. Because CKD is often under-recognized, understanding who is at a higher risk can be beneficial in identifying patients who need long-term follow-up and early preventive actions to ensure proper renal function.