Menstrual Cycle and Miscarriage

Miscarriage risk is 67% lower with 30-31 day cycles, 60% less likely after long menstrual bleeds

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.

Recurrent miscarriage linked to shorter follicular phase (14 vs 16.2 days)

Women with a history of miscarriage tended to have shorter follicular phases (14.0 vs 16.2 days), adjusted for both age and recent oral contraceptive use.

Miscarriage risk was normalized by simply lengthening short follicular phase

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.

Miscarriage risk doubles in women with follicular phases shorter than 12 days or longer than 16

Charts of 206 consecutive pregnancies occurring in couples seen because of infertility were analyzed in an attempt to identify factors, apparent at the time of conception, which may impose risks on pregnancy outcome. Although the mean age was similar in both groups, women 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.

Fertility is 53% lower in women who ovulate before day 11

The present study was designed to evaluate whether there is a lower pregnancy rate in women with short follicular phases, as defined by attaining the peak 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.

Long menstrual cycles raises risk of miscarriage by 130%

Long cycles (36 days or more), irregular cycles, and intermenstrual bleeding were associated with a history of infertility. Long or irregular cycles were each associated with more than twice the odds of infertility. Intermenstrual bleeding was also associated with increased odds of infertility. Having long cycles was associated with a doubling in the adjusted odds of having a miscarriage among women who had been pregnant within the last 5 years (odds ratio = 2.3). Results controlled for current age, age when most recent pregnancy ended, current BMI, and smoking during pregnancy.

Other topics covered under Menstrual Cycle and Miscarriage:

How to Normalize the Menstrual Cycle

For a concise list of qualities found to affect one's risk of miscarriage, see: Causes of Miscarriage