Preconceptional folate supplementation and the risk of spontaneous preterm birth: a cohort study. oleh Radek Bukowski, Fergal D Malone, Flint T Porter, David A Nyberg, Christine H Comstock, Gary D V Hankins, Keith Eddleman, Susan J Gross, Lorraine Dugoff, Sabrina D Craigo, Ilan E Timor-Tritsch, Stephen R Carr, Honor M Wolfe, Mary E D'Alton