@article{Kramer1998,
author = {Kramer, M.S. and Platt, R. and Yang, H. and Joseph, K.S. and Wu Wen, S. and Morin, L. and Usher, R.H.},
title= {Secular trends in preterm birth. A hospital-based cohort study},
year = {1998},
doi = {10.1001/jama.280.21.1849},
journal = {JAMA: The Journal of the American Medical Association},
volume = {280},
number = {21},
pages = {1849--1854},
}