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Fertility

Fertility is the natural capability of giving life. As a measure, "Fertility Rate" is the number of children born per couple, person or population. This is different to fecundity, which is defined as the potential for reproduction (influenced by gamete production, fertilisation and carrying a pregnancy to term). 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. Infertility is a deficient fertility.

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.

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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.

Demography

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 ratio of women relative to men in populations 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.

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. Men can ejaculate and produce sperm at any time of the month, but their sperm quality dips occasionally, which scientists guess is in relation to their internal cycle.

Furthermore, age also plays a role, especially for women.

Menstrual cycle

Main article: Menstrual cycle#The fertile window

Women are fertile only about seven days in each menstrual cycle. Ovulation occurs at about the fourteenth day of their menstrual cycle, this obviously being the most fertile time for females. The exact point of ovulation varies, however^[1]. If the egg is not fertilized by the male’s sperm, the egg will break down within 1–2 days into its components (mostly protein) and be reabsorbed by the body. However, sperm can survive inside the uterus for five days. Thus, a successful conception can result during seven days of the female cycle; five days before and two days after ovulation.

Female fertility after 30

Women's fertility peaks around the age of 23-24, and often deteriorates after 30. With a rise in women postponing pregnancy,^[2] this can create an infertility problem. Of women trying to get pregnant, without using fertility drugs or in vitro fertilization:

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.^[3]

The above figures are for pregnancies ending in a live birth and take into account the increasing rates of miscarriage in the ageing population. According to the March of Dimes, "about 9 percent of recognised 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".^[4]

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."^[5]

The use of fertility drugs and/or in vitro fertilization can increase the chances of becoming pregnant at a later age. Successful pregnancies facilitated by fertility treatment have been documented in women as old as 67.^[6]

Doctors recommend that women over 30 who have been unsuccessful in trying to conceive for more than 6 months undergo some kind of fertility testing ^[7].

Male fertility and age

Although erectile dysfunction increases with age,^[8] male fertility does not decline as it does with females; there have been examples of males being fertile at 94 years old.^[8] At most, age "might possibly result in a moderate decline" in fertility in males.^[8]

Cause of decline

Sperm count declines slightly with age, with men aged 50-80 years producing sperm at an average rate of 75% compared with men aged 20-50 years. However, an even larger difference is seen in how many of the seminiferous tubules in the testes contain mature sperm;

In males 20-39 years old, 90% of the seminiferous tubules contain mature sperm.
In males 40-69 years old, 50% of the seminiferous tubules contain mature sperm.
In males 80 years old and older, 10% of the seminiferous tubules contain mature sperm.^[8]

This does not directly correlate with any absolute decline in fertility, since there are still many sperm cells left for fertilization. ^[8]

Infertility

see also Infertility

References

^ Ovusoft.com
^ http://findarticles.com/p/articles/mi_m1077/is_1_62/ai_n16807720 "Late-in-life Pregnancy"
^ Fertility Treatment Less Successful After 35. WebMD. Retrieved on July 4, 2006.
^ Pregnancy After 35. March of Dimes. Retrieved on July 4, 2006.
^ The sterility tax can be reestablished in Russia. Retrieved on September 22, 2006.
^ Spanish woman ' is oldest mother'. BBC News. Retrieved on 2006-12-30.
^ [http://fertilitytesting.co.uk/female_fertility_tests.html Fertility Testing] (Female Fertility Testing)
^ ^a ^b ^c ^d ^e Effect of Age on Male Fertility Seminars in Reproductive Endocrinology. Volume 9, Number 3, August 1991. Sherman J. Silber, M.D.