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OVULATION
occurs on only one day in the cycle and is followed about 2 weeks
later by menstruation, in the absence of pregnancy. Normally the
time between ovulation and the next menstruation does not vary to
any great extent. The length of the menstrual cycle is dependent
upon variations in the time from the beginning of the cycle up to
ovulation, as illustrated below.
The occurrence of ovulation determines the length of the cycle:
The length of time from the beginning of menstruation up to ovulation
can vary. Ovulation is often delayed at times of
stress, during lactation and at pre-menopause.
On this one day of ovulation in the cycle, one or more ova may
become available for fertilization. The ovum lives for no more than
24 hours, and the sperm cells for a variable time. In the absence
of satisfactory mucus the sperm cells are unlikely to survive beyond
an hour or so, but with the support of good cervical
mucus they may survive for up to 2 or 3 days, even rarely 4
or 5 days.
For further illustrations of variable cycle length click
here.
Reference: Evelyn L.
Billings, John J. Billings and Maurice Catarinich, Billings
Atlas of the Ovulation Method, the Mucus Patterns of
Fertility and Infertility, Ovulation Method Research
and Reference Centre of Australia, Melbourne, 1989.
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