 Males
are fertile all the time
after beginning sperm production
- Females are fertile for a period
of time during each cycle
- Menstrual cycle:
- begins with menstrual bleeding
- ovulation occurs
- if egg is not fertilized, cycle begins again in
about 2 weeks
- Fertile time can begin about 6 days before ovulation
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Young people need to understand when they are fertile and when
sexual activity can lead to pregnancy. In men, sperm production
starts during puberty. Once this begins, men's bodies produce
sperm continuously. Thus men are fertile all the time, typically
for the rest of their lives.
Women are fertile for a short period of time during each menstrual
cycle, from menarche until menopause when menstrual bleeding
ends. This occurs at about age 45 to 50. The menstrual cycle
is governed by a series of hormonal changes and generally varies
in length from 21 to 36 days. The cycle begins with the first
day of menstrual bleeding, which is the shedding of the uterine
lining. Hormonal changes then lead to ovulation, when the egg
is released from the ovary.
The number of days from the beginning of the cycle until ovulation
varies. For most women, ovulation usually occurs 14 days before
the initiation of the next menstrual bleeding. This means for
a 28-day cycle, which is about average and is shown in the slide,
ovulation occurs around day 14. In a 24-day cycle, ovulation
would occur at about day 10, and in a 34-day cycle, at about
day 20. For women with irregular cycles, it is particularly
difficult to predict the day of ovulation.
After ovulation occurs, the egg can survive up to 24 hours.
However, sperm can survive in the woman's reproductive tract
for up to five days, so sperm deposited before ovulation can
fertilize the egg. Thus, the fertile time for a couple —
when it is unsafe to have unprotected intercourse — could
begin six days before ovulation and last for 24 hours after
ovulation. If fertilization occurs, the lining of the uterus
is not shed and there is no menstrual bleeding. A missed menstrual
period is often the first sign of pregnancy. If the egg is not
fertilized, the cycle begins again about two weeks later, with
another shedding of the uterine lining.
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