Vitamin D status and recurrent preterm birth: a nested case-control study in high-risk women

Please cite this paper as: Thorp J, Camargo C, McGee P, Harper M, Klebanoff M, Sorokin Y, Varner M, Wapner R, Caritis S, Iams J, Carpenter M, Peaceman A, Mercer B, Sciscione A, Rouse D, Ramin S, Anderson G. Vitamin D status and recurrent preterm birth: a nested casecontrol study in high-risk women. BJOG 2012;119:16171623. Objective To determine whether vitamin D status is associated with recurrent preterm birth, and any interactions between vitamin D levels and fish consumption. Design A nested casecontrol study, using data from a randomised trial of omega-3 fatty acid supplementation to prevent recurrent preterm birth. Setting Fourteen academic health centres in the USA. Population Women with prior spontaneous preterm birth. Methods In 131 cases (preterm delivery at <35 weeks of gestation) and 134 term controls, we measured serum 25-hydroxyvitamin D [25(OH)D] concentrations by liquid chromatography-tandem mass spectrometry (LC-MS) from samples collected at baseline (1622 weeks of gestation). Logistic regression models controlled for study centre, maternal age, race/ethnicity, number of prior preterm deliveries, smoking status, body mass index, and treatment. Main outcome measures Recurrent preterm birth at <37 and <32 weeks of gestation. Results The median mid-gestation serum 25(OH)D concentration was 67 nmol/l, and 27% had concentrations of <50 nmol/l. Serum 25(OH)D concentration was not significantly associated with preterm birth (OR 1.33; 95% CI 0.483.70 for lowest versus highest quartiles). Likewise, comparing women with 25(OH)D concentrations of 50 nmol/l, or higher, with those with <50 nmol/l generated an odds ratio of 0.80 (95% CI 0.381.69). Contrary to our expectation, a negative correlation was observed between fish consumption and serum 25(OH)D concentration (-0.18, P < 0.01). Conclusions In a cohort of women with a prior preterm birth, vitamin D status at mid-pregnancy was not associated with recurrent preterm birth.