An increase in the plasma oestrogen:progesterone ratio precedes labour in sheep, and an increase in the saliva oestriol:progesterone ratio has recently been demonstrated in women prior to spontaneous term and preterm labour. Studies were undertaken to further investigate the hormonal changes of pregnancy, particularly in relation to the onset of labour, and ultrasound examinations were performed to determine whether fetal adrenal size correlates with maternal steroid hormone levels. Absorption of progesterone was also studied in pregnancy, with a view to the possible prevention of preterm labour in some women at a later date. A rise in the saliva oestriol:progesterone ratio, prior to labour, was found in 68% of 28 normal women, and a ratio above the 90th centile for the gestation was found in 47% of the 17 women who went into idiopathic preterm labour. On serial monthly ultrasound examinations fetal adrenal size increased linearly; there was no correlation between adrenal and hormonal measurements at a given gestation. Adrenal size decreased rapidly during the first six weeks of neonatal life. Maternal plasma oestrone, oestradiol, oestriol, progesterone, dehydroepiand-rosterone sulphate, sex hormone binding globulin, human chorionic gonadotrophin, human placental lactogen and prolactin, and saliva oestrogen and progesterone levels were measured fortnightly from 20 weeks gestation in 20 normal women. Levels were comparable with previous studies; no interrelationships of significant importance were detected. Hourly saliva cortisol levels were significantly increased in late pregnancy, but the diurnal variation was maintained. The increase in plasma and saliva cortisol levels was not caused by the increased corticosteroid binding globulin levels. Thus an increased oestriol:progesterone ratio in the majority of women prior to term and idiopathic preterm labour was demonstrated, but it was concluded that neither saliva oestriol and progesterone, nor fetal adrenal ultrasound measurements, would be helpful in the prediction of preterm labour, in practice
