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In medicine, the definition of fertility is "the capacity to establish a clinical pregnancy." [24] Women have hormonal cycles which determine when they can achieve pregnancy. The cycle is approximately twenty-eight days long, with a fertile period of five days per cycle, but can deviate greatly from this norm.
A woman's fertility is affected by her age. The average age of a girl's first period is 12–13 (12.5 years in the United States, [4] 12.72 in Canada, [5] 12.9 in the UK [6]), but, in postmenarchal girls, about 80% of the cycles are anovulatory in the first year after menarche, 50% in the third and 10% in the sixth year. [7]
Fertility problems affect one in seven couples in the UK. Most couples (about 84%) who have regular sexual intercourse (that is, every two to three days) and who do not use contraception get pregnant within a year. About 95 out of 100 couples who are trying to get pregnant do so within two years. [90] Women become less fertile as they get older.
Around 35, fertility is noted to decline at a more rapid rate. [1] At age 45, a woman starting to try to conceive will have no live birth in 50–80 percent of cases. [2] Menopause, or the cessation of menstrual periods, generally occurs in the 40s and 50s and marks the cessation of fertility, although age-related infertility can occur before ...
Natural fertility is a concept developed by the French historical demographer Louis Henry to refer to the level of fertility that would prevail in a population that makes no conscious effort to limit, regulate, or control fertility, so that fertility depends only on physiological factors affecting fecundity.
"Coition of a Hemisected Man and Woman" (c. 1492) by Leonardo da Vinci. Human reproduction normally begins with copulation, though it may be achieved through artificial insemination, and is followed by nine months of pregnancy before childbirth. Pregnancy can be avoided with the use of contraceptives such as condoms and intrauterine devices. [9]
Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, [1] [2] [3] the natural capability to produce offspring, [4] measured by the number of gametes (eggs), seed set, or asexual ...
There is also considerable variability in this interval, with a 95% prediction interval of the ovulation of 9 to 20 days after menstruation even for an average woman who has a mean LMP-to-ovulation time of 14.6. [31] In a reference group representing all women, the 95% prediction interval of the LMP-to-ovulation is 8.2 to 20.5 days. [30]