Ultrasound examination of the ovaries was performed in the first and/o
r second half of three consecutive cycles in 3 groups of women; Group
T who had been using a levonorgestrel triphasic oral contraceptive for
at least 6 months, Group P who had been using a progestogen-only pill
for at least 6 months, and Group C, a control group. Any follicles gr
eater than 10 mm in diameter and any cysts were measured. Fifty-three
scans were performed in Group T, 45 in Group P and 31 in Group C. Only
4 follicles were detected in 17 women in Group T compared to 10 folli
cles in 15 women in Group P and 7 follicles in the 10 women in Group C
; all follicles were 25 mm or less in diameter except for 3 follicles
in 2 women. The differences between the groups were not statistically
significant. Four enlarged follicles were detected in 3 women during 5
3 scans in Group T, 15 in 8 women (45 scans) in Group P and only 1 in
31 scans in Group C. Based upon the proportions of scans with enlarged
follicles, the difference between Groups T and P was statistically si
gnificant, indicating that the incidence of enlarged follicles was low
er in women using a combined oral contraceptive than in those using a
progestogen-only pill. Furthermore, the study shows that any enlarged
follicles which occurred were transient.