Some new aspects of the endocrinological response to pregnancy.

Serial measurements of serum progesterone, oestradiol, prolactin, human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) have been determined in 32 healthy women at regular intervals throughout pregnancy. The data confirm previous reports that levels of these hormones vary widely between individuals at each stage of gestation, but further analyses have shown two other features: first there is a clear tendency for individuals to retain their rank in the spectrum of hormone values throughout pregnancy; second when the concentrations of the individual hormones (except hCG) are transformed to logarithmic values, the trends within individuals approximate well to straight lines during the second and third trimester of pregnancy. These findings provide a relatively simple method for describing the rates of change in the concentrations of these hormones and for examining possible relations between them. They also suggest that the quality of the maternal endocrine milieu may be determined at an early stage of gestation.