Population-based register study of children born in Sweden from 1997 to 2014 showed an increase in rickets during infancy

Aim: This population-based study assessed the incidence of rickets in infants up to age of one born in Sweden from 1997 to 2014. We also examined maternal and perinatal factors and co-morbidity. Methods: We used Swedish National Board of Health and Welfare registers and data from Statistics Sweden. The outcome measure was an International Classification of Diseases, Tenth Revision, code for rickets. Results: There were 273 cases of rickets, with an incidence of 14.7 per 100 000 and a 10-fold incidence increase between 1997 and 2014. The majority (78.4%) were born preterm, half were small-for-gestational age (SGA) (birthweight <10th percentile), 4.8% were born to Asian-born mothers and 3.5% to African-born mothers. The adjusted odds ratios by birth week were 182 (95% CI: 121–272) before 32 weeks and 10.8 (95% CI: 6.72–17.4) by 32–36 weeks. Preterm infants with necrotising enterocolitis had very high odds for rickets and so did SGA term-born infants and those born to African-born mothers. The odds for rickets among preterm infants increased considerably during the later years. Conclusion: Rickets increased 10-fold in Sweden from 1997 to 2014 and was mainly associated with prematurity, SGA and foreign-born mothers. Possible reasons may include increased preterm survival rates and improved clinical detection and registration.