THE baby arrives after the contractions start. But what starts the contractions? Researchers have confirmed the exact physiological mechanism responsible – contractions begin when the hormone progesterone stops working.
Progesterone is known to stop the womb contracting. Now Jennifer Condon, Carole Mendelson and colleagues at the University of Texas Southwestern Medical Center in Dallas have analysed tissue samples from women having caesareans and discovered that proteins which activate the progesterone receptor disappear from the womb when labour begins – blocking the effect of the hormone (Proceedings of the National Academy of Sciences, vol 100, p 9518).
