In primiparous women, cervical length at 22–24 weeks' gestation predicts the need for emergency cesarean delivery during labor at term, according to a study of data from more than 27,000 women at hospitals in England.
A long cervix (40–67 mm) at mid-pregnancy was associated with a high risk of intrapartum cesarean delivery at term because of failure of labor to progress, and this risk declined with a decreasing length of the cervix.
“We hypothesize that poor progress during labor at term is determined by the development of the uterus at much earlier stages of pregnancy,” Dr. Gordon C. S. Smith of Cambridge University (U.K.) and his associates wrote in the New England Journal of Medicine.
Animal studies have suggested that preparation of the uterus for labor begins at relatively early stages of gestation.
To explore this issue in humans, Dr. Smith and his coinvestigators conducted a secondary analysis of data collected in a large multicenter study of pregnancy interventions.
That study, which was conducted at eight hospitals in and around London between 1998 and 2006, had included data from transvaginal ultrasound assessment of cervical length at a median of 23 weeks' gestation in 27,472 primiparous women.
A total of 5,542 of the women went on to require cesarean section, almost always because their labor failed to progress.
The rate of caesarean delivery was lowest (16%) among women with a cervical length in the lowest quartile at mid-pregnancy.
The rate of cesarean delivery rose significantly among women in the second quartile (18%), rose significantly again among women in the third quartile (22%), and rose significantly again among women in the highest quartile (26%) of cervical length.
“Rates of cesarean delivery started to rise at a cervical length of 25 mm and plateaued at a cervical length of 50 mm, approximately doubling across the range of observed values,” Dr. Smith and his associates reported (N. Engl. J. Med. 2008;358:1346–53).
“Adjustment for a range of characteristics (maternal age, body mass index, smoking status, race or ethnic group, gestational age at birth, spontaneous or induced labor, birth weight percentile, and hospital of delivery) slightly attenuated but did not eliminate the significant association between cervical length and risk of cesarean delivery at term,” the researchers concluded.
Further study is needed to investigate the possibility that a long cervix in mid-pregnancy may signal dysfunctional development of the uterus, “which is ultimately manifested in the need for cesarean delivery at term,” Dr. Smith and his associates said.