Very few studies have been published on the effects of oral contraception on menstrual cycle parameters. Researchers from the University of Dusseldorf have been collecting charts of Sympto-Thermal users for over 15 years.1 As of July 1, 1998, 22% of the 1,426 women in their data set had previously used oral contraceptives (OCs). From this data set, 175 post-pill women were compared to a similar (according to age and socioeconomic characteristics) group of 284 women who never used OCs. The post-pill women generated 3,048 cycles of data and the control group of women 6,251 cycles. The mean age of the post-pill women was 26.25 years and for the control group 25.29 years.
The results showed that the post-pill group had significantly longer (length) cycles than the control group for up to 9 cycles. Further, with regard to frequency, the post-pill group had significantly longer cycles greater than 35 days for up to 6 cycles.
The follicular phase length (based on the day of the temperature shift minus one day) was significantly longer for up to 8 cycles in the post-pill group. The differences might be as long as 15 cycles, but the number of cycles produced by the post-pill group decreased due to anovulatory cycles or "difficult to interpret" temperature graphs. The biggest difference in the follicular length occurred in the first cycle - with an average prolonged difference of 4 days. There was a significant difference in the first two cycles in the length of the luteal phase, with the post-pill group being shorter, due mostly to insufficient luteal phase lengths (< 10 days). The onset of cervical mucus did not differ between the two groups, but the peak in cervical mucus differed for up to 9 cycles. In the first cycle the average day of peak was 23.19 for the post-pill group and 18.09 for the control group.
The researchers considered major "cycle disturbances" to be those cycles with either a monophasic BBT, a cycle length over 35 days, or a luteal phase of less than 10 days. Although none of these disturbances were found in 51.4% in the first cycle of the post-pill group, there were significantly more of these disturbances among the post-pill group than the control group for up to cycle 7 due primarily to cycles longer than 35 days. The researchers defined the beginning of regular cycling to be the first of 3 subsequent cycles with a luteal phase of at least 10 days. Based on this definition, over 70% of the post-pill group returned to a regular, ovulatory cycle pattern by the 7th cycle.
1 Gnoth, C., Frank-Hermann, P., & Sclunoll, A., et al. Cycle characteristics after discontinuation of oral contraceptives. Gynecological Endocrinology. 2002;16:307-317. [Back]