FOR decades past obstetrician gynaecologists have been telling some women prone to premature birth that they have a condition which, to some, sounds like a rude joke: an "incompetent cervix". Medical textbooks have long taught the conventional wisdom that premature births are more likely to occur when a woman has an "incompetent" cervix, incapable of holding the baby in the womb for the full gestation of the pregnancy. It's an interesting idea, but it's not true, the New England Journal of Medicine has reported.
The actual risk factor for premature birth is not the strength but the length of the cervix, a tough cylinder that functions as the doorway to the womb. Doctors at Ohio State University measured the length of the cervix in 3,000 pregnant women using an ultrasound probe and discovered that women with shorter cervixes face a higher risk of giving birth prematurely. A woman with an average length cervix - about 36 millimetres - had double the risk of a premature delivery compared with women with the longest cervixes. Women whose cervixes were the shortest - only 12 to 24 millimetres long - had a 10 times greater chance of a premature birth. Nevertheless, many women with shorter cervixes were also perfectly capable of carrying babies to full term.