Factors affecting plasma angiotensin II concentration in labour.

Concentrations of plasma angiotensin II (AII) have been measured in the second stage of labour or before delivery by elective Caesarean section in 134 women and some factors influencing the levels have been assessed. Plasma AII concentrations in the second stage of labour were higher than levels previously observed before the onset of labour in both primigravid and multiparous women. Markedly lower levels were found following delivery by elective Caesarean section than following vaginal delivery. Multiparae had higher AII concentrations than primigravidae both before the onset of labour and at delivery. Epidural analgesia was associated with significantly lower AII concentrations; in primigravidae receiving such analgesia a statistically significant relation was found between AII concentration and diastolic blood pressure at delivery. A similar relation was found in the nonproteinuric patients delivered by Caesarean section. The estimated duration of the second stage of labour was the major factor affecting AII concentration in normal multiparae. In both primigravid and multiparous women, AII concentrations were markedly raised in association with proteinuria.