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Fertil Steril. 2008 Oct;90(4):1232-5. doi: 10.1016/j.fertnstert.2007.10.050. Epub 2008 Feb 4.

Variability in the hormonally estimated fertile phase of the menstrual cycle.

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College of Nursing, Institute for Natural Family Planning, Marquette University, Milwaukee, Wisconsin 53201-1881, USA.


The purpose of this study was to determine the variability in length of the fertile phase of the menstrual cycle with 140 participants who produced 1,060 cycles with an electronic hormonal fertility monitor. The length of the fertile phase, as defined by the first day with a threshold level of urinary E3G and ending with a second day above a threshold of LH, varied from <1 to >7 days, with the most frequent length being 3 days.

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