@article{Astolfi1999,
author = {Astolfi, P. and Zonta, L.A.},
title= {Risks of preterm delivery and association with maternal age, birth order, and fetal gender},
year = {1999},
doi = {10.1093/humrep/14.11.2891},
volume = {14},
number = {11},
pages = {2891--2894},
}