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For
couples with normal fertility, a single act of unprotected intercourse during
the middle two weeks of the menstrual cycles carries about an 8% chance of
pregnancy.
For all couples having regular, unprotected intercourse of 1-3 times a week,
who are neither seeking nor avoiding a pregnancy, the pregnancy rate is about
20% in the first month. In the second month, the pregnancy rate is about 20% of
the remainder, and by the end of the third month, about half are pregnant.
About 85% will be pregnant at the end of one year of unprotected intercourse.
Other factors influence fertility, however. Peak fertility rates occur when a
woman is in her 20's and gradually declines after age 30. By her mid-40's, even
though she continues to have regular menstrual flows, her natural fertility
usually will have declined to about that of a 22 year old who uses a diaphragm
for contraception.
The mid-cycle surge in LH, FSH, and estrogen that accompanies ovulation
stimulates, in some women, an increase in sexual feelings and responsiveness to
sexual initiatives by her partner. The consequences of these impulses are an
increased likelihood of conception at that particular time of the menstrual
cycle.
Frequency of intercourse also influences fertility. Couples having
intercourse once or twice a month are less likely to conceive than those having
intercourse several times a week.
Frequency of ovulation is important. Women whose menstrual cycles are every
40-60 days are significantly less fertile, not only because of the diminished
opportunity for fertilization, but also because many of these women have some
degree of insulin resistence, which lengthens the cycle frequency and also
affects the quality of the eggs released.
There is no single best contraceptive technique for all people under all
circumstances. A diaphragm may be a good choice for one couple and a terrible
choice for another couple. An IUD might be a bad idea for a women at one stage
in her life and an excellent choice for the same woman at another stage in her
life. For these reasons, it is important for the physician to be skilled at
counseling individuals in contraceptive techniques, to help them meet their
contraceptive goals.
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