Looking For That Fertile Window?, Page 2

The Study Results

Of 696 cycles observed in 213 women:

2% were fertile by cycle day 4
17% were fertile by cycle day 7
54% were fertile by cycle day 12 or 13
women who reported usual cycles of 27 days or less ovulated, and therefore were fertile, earlier than those with cycles longer than 27 days
estimated one third of women with short cycles reached fertility by end of cycle week one
calculated a 1-6% probability of being fertile on the day the next period was expected
greater than 70% are fertile either before cycle day 10 or after cycle day 17
some women are potentially fertile during most of the days in their cycle

It is important to note that the cycle days usually described as the fertile window are still considered to be the five days prior to ovulation and the day of ovulation itself.

This study found no evidence supporting the opinion that ovulation prior to cycle day 13 indicates a less fertile cycle. One participant's ovulation on cycle day 8 resulted in a successful pregnancy.

The researchers sought to update assumptions about women's most fertile times, and they have succeeded. Current assumption is that, on average, women ovulate 14 days prior to next menstrual period. In this study of 213 women, out of 69 28-day (thought to be the norm) cycles, ovulation occurred 14 days prior to menses in only ten percent. Ovulation was noted to occur from cycle day 10 to 22, and at least 10% of regular-cycled women were fertile on any given day between cycle days 6 and 21. The outer ends of the fertility spectrum, adolescence and perimenopause, provide even less predictability.

What Does It All Mean?

Aside from confirmation that some women really are much more fertile than ever before believed, and validation that the calendar method of predicting fertility is fruitless, the results of this study mean that, for some couples who are trying to conceive, timing intercourse precisely need not be the focus it has been. Again note: this study excluded any women with known fertility problems. However, for those who are of average fertility (and all other factors leading to successful conception are in place and functioning), these researchers suggest that conception should occur through sexual intercourse twice or more times a week -- without even looking at the calendar.

On one of this site's favorite topics, using sympto-thermal methods or home kits to predict ovulation, Dr. Wilcox concludes, "(Those methods) are fine for detecting the day of ovulation, but still leave much to be desired in predicting the prior fertile window."