Due dateResearch on 'Length of human pregnancy and contributors to its natural variation' has been published in the reproductive medicine journal, Human Reproduction. 

Commenting on the research, MerviJokinen, practice and standards professional advisor at the Royal College of Midwives, said: "This is interesting and useful research. However, midwives have never regarded the due date as anything other than a rough indication of when a woman may give birth. 

"This study and our knowledge of physiology show that the norm for the duration of pregnancy is 37-42 weeks. It reaffirms our experience that every woman is different. As practitioners we should be cautious about intervening too early as every individual has their own pattern of pregnancy. 

"I do not think that this signals the end of midwives and other health professionals giving a woman a single due date. It should be explained to the woman that the due date is always an estimate and as this research and our experience shows, this can vary widely."