We prospectively studied 470 women to determine whether cycle length or bleed length were associated with fertility or miscarriage. Pregnancy was most likely to occur after cycles lasting 30 to 31 days and 40% less likely after shorter cycles. Miscarriage was three times more common after cycles that were either shorter than or longer than 30 to 31 days (for shorter cycles, odds ratio = 3.0 and for longer cycles odds ratio = 3.0). Conception occurred most frequently after menstrual bleeds lasting at least 5 days, and miscarriage was 60 percent less likely after periods lasting greater than 5 days, when compared with 5-day bleeds.
miscarriage tended to have shorter follicular phases (14.0 vs 16.2 days), adjusted for both age and recent oral contraceptive use.
The clinical and viable pregnancy rates of infertile patients were matched to similar controls who ovulated at or past day 11. After 2-3 cycles of demonstrating ovulation before day 11 some patients were treated with ethinyl estradiol, 20 mcg daily, from day 2 of the cycle until ovulation. Clinical and viable pregnancy rates for the normal ovulators (84.4%, 59.3%) were significantly higher than the rates for early ovulators (21.8%, 9.3%). However, the pregnancy rates were 83.3% and 66.7% for the subset of early ovulators who were made to ovulate later by ethinyl estradiol. CONCLUSIONS: The short follicular phase per se reduces fertility.
35 years or older had a significantly higher incidence of miscarriage than younger women. Data collected from basal body temperature charts suggested a slightly higher risk for miscarriage in women with previous anovulatory cycles. The mean follicular phase in the conception cycle was 16 days in both groups. However, a twofold increase in miscarriage rate was noticed in conceptions with follicular phases shorter than 12 days or longer than 16 days, in comparison with those with follicular phases of 13-15 days' duration. The mean daily temperature increment in the early luteal phase was the same in both groups. No relation between sperm count or motility and miscarriage was observed.
estrogen level before day 11 of the cycle. Thirty-two early ovulators with mature follicles were matched with 32 women being treated for similar infertility problems, who ovulated between days 12-20. Pregnancies were achieved by 9 (28.1%) of the early ovulators compared to 19 (59.4%) of the controls. The mean number of cycles required to achieve a pregnancy was 8.6 in the early ovulators compared to 6.4 in the controls. Using the clinical life table method, the 12-month pregnancy rate was estimated to be 31.4% for early ovulators as compared to 66.3% for controls.
How to Normalize the Menstrual Cycle
For a concise list of qualities found to affect one's risk of miscarriage, see: Causes of Miscarriage