Endocrine changes in premature labour.

Plasma oestradiol and progesterone levels in peripheral blood have been studied before and during premature labour of unknown aetiology. Hormones were measured by radio-immunoassay using specific antisera. Levels in patients who delivered prematurely were compared with levels measured serially in 33 primigravidae during normal pregnancy and labour.In 19 out of 25 patients admitted in progressive premature labour the plasma oestradiol level was two standard deviations or more above the mean for the control patients of similar gestational age. The mean (+/- S.E. of mean) plasma oestradiol in premature labour was 19.1 +/- 1.1 ng/ml, similar to levels found in labour at term (18.5 +/- 1.4 ng/ml). In contrast, in over 50% of cases levels of plasma progesterone during premature labour lay below the mean for gestation though within the normal range. In six patients studied serially oestradiol levels rose dramatically, high values being detected one to 10 days before the onset of premature labour. Serial progesterone levels gave no consistent trend though one patient showed steadily decreasing values.These studies suggest that the onset of premature labour is preceded by a marked increase in peripheral plasma oestradiol levels, which may be of value not only in the prediction of premature labour but also in its prevention by suppression of the premature oestradiol surge.