Fertility

From Wikipedia, the free encyclopedia

Fertility is the ability of people or animals to produce healthy offspring in abundance, and of the earth to bear fruit. In the English language, the term was originally applied only to females, but increasingly is applied to males as well, as common understanding of reproductive mechanisms increases and the importance of the male role is better known. The opposite of fertility is infertility.

Human fertility depends on factors of nutrition, sexual behavior, culture, instinct, endocrinology, timing, economics, way of life, and emotions. Animal fertility is no less complex, and may display astounding mechanisms.

1 Agriculture
2 Demographics
3 Human fertility
- 3.1 Female Fertility After 30
4 See also
5 References

[edit] Agriculture

See also arable land, soil fertility, harvest, Neolithic revolution.

Fertility is also applied to farmlands and plants, where it implies a capacity to yield large crops of sound fruits, seeds or vegetables.

[edit] Demographics

The fertility rate is a demographic measure of the number of children per woman. Although it has been until recently considered to be a fairly reliable indicator of population growth, it is no longer so in much of Asia. Due to selective abortion and other factors, the number of women themselves is declining. Therefore, the fertility rate as it has traditionally been defined is no longer an authoritative measure of population growth in China, India, and Myanmar.

[edit] Human fertility

Main article: Human fertility

Both women and men have hormonal cycles which determine both when a woman can achieve pregnancy and when a man is most fertile. The female cycle is approximately twenty-eight days long, but the male cycle is variable. Women ovulate at about the fourteenth day of their cycle, this obviously being the most fertile time for females. Men can ejaculate and produce sperm at any time of the month, but their libido dips occasionally, which scientists guess is in relation to their internal cycle. A study done in Mexico suggests that men's libido levels are also sometimes correlated to their partner's monthly cycle.

During the fourteenth week of fetal growth, the eggs (or ova) form in the ovaries of a female fetus, where they will remain until puberty. At puberty, the eggs will eventually start to mature one-by-one. At ovulation, the egg bursts from the ovary sometimes causing a small, sharp pain called mittelschmerz (German for "middle pain"). If the egg is not fertilized by the male’s sperm, the egg will break down within twenty-four hours into its components (mostly protein) and be reabsorbed by the body.

A study suggests that women dress more provocatively when they are at their most fertile [1].

[edit] Female Fertility After 30

Women's fertility peaks in their early twenties, and often deteriorates after 30. Of women trying to get pregnant, without using fertility drugs:

At age 30, 75% will get pregnant within one year, and 91% within four years.
At age 35, 66% will get pregnant within one year, and 84% within four years.
At age 40, 44% will get pregnant within one year, and 64% within four years.¹

Those figures are for conception, not for the birth of a healthy baby. According to the March of Dimes, "about 9 percent of recognized pregnancies for women aged 20 to 24 ended in miscarriage. The risk rose to about 20 percent at age 35 to 39, and more than 50 percent by age 42."²

Birth defects, especially those involving chromosome number and arrangement, also increase with the age of the mother. According to the March of Dimes, "At age 25, a woman has about a 1-in-1,250 chance of having a baby with Down syndrome; at age 30, a 1-in-1,000 chance; at age 35, a 1-in-400 chance; at age 40, a 1-in-100 chance; and at 45, a 1-in-30 chance."³

Multiplying the conception rate times the miscarriage rate times the birth defect rates should yield a rough likelihood of a healthy birth: