Steroid concentrations in fluid from 138 ovarian antral follicles obtained from 30 pregnant women were measured and compared with those in aspirates of 151 follicles of similar size (i.e. diameter 2–6 mm) from 61 non-pregnant women who had normal regular menstruations. The follicles were classified as healthy or atretic by flow cytometric DNA measurement of the granulosa cells contained in the follicular fluid aspirate.
Nine (7%) of the follicles from pregnant women and 21 (14%) of those from non-pregnant women were healthy, and the remainder atretic (P>0·05). Androstenedione was the most abundant steroid in all follicles. Mean progesterone levels in follicular fluid from pregnant women were significantly (P<0·05) higher than in follicular fluid from non-pregnant women. In pregnant women progesterone levels were significantly (P<0·01) higher in fluid from healthy than from atretic follicles. In contrast, no significant differences in steroid concentrations were found between fluid from healthy and atretic follicles in non-pregnant women.
We conclude that antral ovarian follicles may develop normally to a diameter of around 6 mm during the third trimester of human pregnancy. We also conclude that these follicles accumulate steroids in the follicular fluid in amounts which equal those found in follicles of similar size in the ovaries of non-pregnant women, but that the composition of intrafollicular steroids during pregnancy is modified towards higher concentration of progesterone. The reason for this increased intrafollicular progesterone level is unclear.