Variability in the hormonally estimated fertile phase of the menstrual cycle

The Fertile Window and Biomarkers: A Review and Analysis of Normal Ovulation Cycles

“…The starting point to detect the onset of the fertile period inside the fertile window has been defined as detection of the beginning of the surge in oestrone-3-glucuronide and the end point, as the second consecutive day at peak LH. This conclusion is based on normal cycles (24,29). However, a good correlation also has been observed between the signals of the start and end of the fertile period in cycles of sub-fertile women with regular menstrual periods with no specific pathology and without hormone therapy (70).…”

“…The American Society for Reproductive Medicine has defined the length of the fertile period as the first day oestrone-3-glucuronide (E3G) is detected in urine up to the second day after the luteinizing hormone (LH) peaks, which usually varies between <1 to >7 days (24). Currently, most studies define the period of greatest fertility as -6 days before ovulation and lasting until one (1) day after ovulation.…”

“…Based on the use of urinary LH peaks as a marker for ovulation, it is possible to conclude that a 50% surge in E3G concentration over the average of the last three values can be used to locate the start of the fertile period (14). Others studies show the use of E3G is 83%, 89% and 90% successful in outlining the potentially fertile period (26,27,24).…”

“…This method has a well-established biological justification, seeing as estrogenic-dependent cervical mucus increases about 5-6 days prior to the day of ovulation (67). Most of the studies that compare the fertile window to cervical mucus to identify the fertile period detect a longer interval with cervical mucus, compared to the classical tools used by the American Society for Reproductive Medicine (24). Adlecreutz compared this interval to cervical mucus and found the cervical mucus overestimates the actual length of the sixday fertile period by an additional four days, on average.…”

Efficacy and Efficiency in Natural Family Planning Services

“…I found similar patterns of the estrogen-threshold estimated length with those in the Netherlands study, but the beginning of mucus clearly over-estimated the fertile phase. 12 We recently compared the number of fertile days as determined by mucus observations with the fertile days indicated by use of the CEFM among women who were breastfeeding and not ovulating. 13 The amount of fertile days (i.e., days of abstinence) with use of the fertility monitor was 17 percent of the total, whereas, the cervical-mucus observations indicated approximately 50 percent of the total days as fertile.…”