Introduction: This study examined whether maternal plasma progesterone and corticotropin releasing hormone (CRH) concentrations can predict the likelihood of preterm labour. Materials and Methods: Maternal plasma progesterone and CRH concentrations were examined in a total of 51 women. The subject cohort included 20 women who were followed from the beginning of the third trimester (28 to 34 weeks gestation), half of whom delivered early preterm and half of whom were not in labour and subsequently delivered at full term (n = 10 per group). In a follow-up experiment, 31 women who were admitted during labour for delivery were examined, 15 of whom delivered preterm and 16 of whom delivered at full term. Comparisons between women who delivered preterm and those who delivered at full term were made by t-tests. Results: Mean progesterone concentration was approximately 30% lower at 28 to 34 weeks gestation in women who delivered prematurely than in women who delivered at term (P <0.001). Meanwhile, mean CRH concentration was 6-fold higher at 28 to 34 weeks gestation in women who experienced spontaneous preterm labour than in those who went into labour at term (P <0.001). Preterm mothers had lower progesterone (P <0.05) and CRH (P <0.01) levels during active labour than full-term mothers. Progesterone levels normalised within 24 hours of delivery in preterm mothers, while CRH levels remained slightly elevated (P <0.01). Conclusions: Maternal progesterone and CRH measurements taken early in the third trimester may be of use as biochemical markers of pregnancies at high risk of premature labour. Introduction: This study examined whether maternal plasma progesterone and corticotropin releasing hormone (CRH) concentrations can predict the likelihood of preterm labour. Materials and Methods: Maternal plasma progesterone and CRH concentrations were examined in a total of 51 women. The subject cohort included 20 women who were followed from the beginning of the third trimester (28 to 34 weeks gestation), half of whom delivered early preterm and half of whom were not in labour and subsequently delivered at full term (n = 10 per group). In a follow-up experiment, 31 women who were admitted during labour for delivery were examined, 15 of whom delivered preterm and 16 of whom delivered at full term. Comparisons between women who delivered preterm and those who delivered at full term were made by t-tests. Results: Mean progesterone concentration was approximately 30% lower at 28 to 34 weeks gestation in women who delivered prematurely than in women who delivered at term (P <0.001). Meanwhile, mean CRH concentration was 6-fold higher at 28 to 34 weeks gestation in women who experienced spontaneous preterm labour than in those who went into labour at term (P <0.001). Preterm mothers had lower progesterone (P <0.05) and CRH (P <0.01) levels during active labour than full-term mothers. Progesterone levels normalised within 24 hours of delivery in preterm mothers, while CRH levels remained slightly elevated (P <0.01). Conclusions: Maternal progesterone and CRH measurements taken early in the third trimester may be of use as biochemical markers of pregnancies at high risk of premature labour.

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