Abstract
Intra-abdominal (vesical), intra-uterine and intra-vaginal pressures were measured in 12 healthy women early in the first stage of labour. Ten subjects were primigravidae and two gravidae-2.
Seven subjects exhibited no significant change of intraabdominal or intra-vaginal pressures during uterine contractions.
Five subjects (4 primigravidae) exhibited no significant change of intra-abdominal pressure but a large and significant increase of intra-vaginal pressure concomitant with uterine contractions. In spite of having higher intrauterine peak pressures during contractions, these subjects exhibited significantly smaller expulsive uterine pressures than the former group because of high vaginal counterpressures. It is believed that increased tension of pelvic floor muscles contributes to the elevated vaginal pressure during contraction.
Our findings may offer a better understanding of why pain relief in selected patients will aid in accelerating labour and make the birth process less hazardous for the fetus.