The concentration of testosterone (ng/100 ml; mean ± sd) has been determined in peripheral venous plasma at 4 hourly intervals for 24 h from 9 non-pregnant women (39.8 ± 11.8) and 9 during late pregnancy (70 ± 32). In addition, the level of this hormone has been measured in samples of plasma removed daily (between 08.30 and 10.00 h) throughout 9 ovarian cycles (41.6 ± 11.8), and weekly from 10 women during gestation (57.6 ± 14.7).
The results show that there is considerable individual variation in both the concentration and pattern in serial samples over the respective time scales. The values of the arithmetic mean from non-pregnant subjects show that there is a tendency for the concentration to be lower between 20.00 and 04.00 h. However, the differences between the values at defined times over a 24 h period are not statistically significant. During the ovarian cycle 3 subjects had peak values during the peri-ovulatory phase, 2 in the luteal, 1 in the follicular and 3 showed no consistent pattern. There was no significant difference in values (40.9 ± 11.8, 41.9 ± 11.9 and 41.8 ± 11.9) for the 3 phases of the cycle. There is a significant rise in the concentration of plasma testosterone during pregnancy (P< 0.0005), but the pattern of the arithmetic mean is not related to the corresponding values for progesterone or oestradiol. During late pregnancy (34 weeks to term) there is a change in the nycterohemeral pattern, with the highest mean values occurring between 16.00 and 04.00 h. The results are discussed.