RT Journal Article SR Electronic T1 Sources of Seasonal Variation in Recorded Length of Gestation JF British Journal of Preventive & Social Medicine JO Br J Prev Soc Med FD BMJ Publishing Group Ltd SP 128 OP 132 DO 10.1136/jech.17.3.128 VO 17 IS 3 A1 R. G. Record A1 Ian Leck YR 1963 UL http://jech.bmj.com/content/17/3/128.abstract AB