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 from 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.
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.
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.
Both women and men have hormonal cycles which determine both when a woman can achieve pregnancy and when a man is most virile. 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.
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. 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.
Women's fertility peaks around the age of 23-24, and often deteriorates after 30. With a rise in women postponing pregnancy, this can create an infertility problem. Of women trying to get pregnant, without using fertility drugs or in vitro fertilization:
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".
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."
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.
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.
Erectile dysfunction increases with age, but fertility does not decline in men as sharply as it does in women. There have been examples of males being fertile at 94 years old.
This does not directly correlate with any absolute decline in fertility, since there are still many sperm cells left for fertilization.
Aging sperm can be a significant and sometimes the sole cause of severe health and developmental problems in offspring, including autism, schizophrenia, and cancer. The older the father, the higher the risk of problems.
The older the man, the more fragmented the DNA in his ejaculated sperm, resulting in greater risk for infertility, miscarriage or birth defects. Up to a third of all cases of schizophrenia are linked to increasing paternal age. Men 40 and older are nearly six times more likely to have children with autism than men under age 30.
''see also Infertility
This article is based on "Fertility" from the free encyclopedia Wikipedia (http://en.wikipedia.org). It is licensed under the terms of the GNU Free Documentation Licencse. In the Wikipedia you can find a list of the authors by visiting the following address: http://en.wikipedia.org/w/index.php?title=Fertility&action=history