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Induction of labour in women with normal pregnancies at or beyond term

Gülmezoglu AM, Crowther CA, Middleton P, Heatley E
Published Online: 
13 June 2012

A normal pregnancy lasts about 40 weeks from the start of the woman's last menstrual period, but anything from 37 to 42 weeks is considered as being within the normal range. Births before 37 weeks are considered preterm because these babies often have breathing difficulties and other problems as some of their organs are not yet fully matured. Births after 42 weeks seem to carry a slightly increased risk for the baby and are associated with a greater number of deaths. No tests can tell if a baby would be better to be left in the womb or labour induced and the baby be born, so arbitrary time limits have been suggested. This review set out to determine if induction of labour at a prespecified time could reduce the risks for the baby. The review found 22 trials involving over 9000 women given induction of labour at various times from 37 weeks to over 42 weeks' gestation; some were quite old trials and the quality was variable. The review grouped the trials by a policy of induction at (1) 37 to 39 weeks, (2) 39 to 40 weeks, (3) < 41 weeks, (4) 41 weeks, and (5) > 41 weeks, compared with a policy of waiting to a later date. There were fewer baby deaths when a labour induction policy was implemented. Such deaths were rare with either policy. Signficantly fewer babies developed meconium aspiration syndrome and fewer caesarean sections were required in the induction group compared with the expectant management group. Women's experiences and opinions about these choices have not been adequately evaluated.