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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.
Additional recommended knowledge
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 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.
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.
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, 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 .
Male fertility and age
Although erectile dysfunction increases with age, male fertility does not decline as it does with females; there have been examples of males being fertile at 94 years old. At most, age "might possibly result in a moderate decline" in fertility in males.
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;
This does not directly correlate with any absolute decline in fertility, since there are still many sperm cells left for fertilization. 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fertility". A list of authors is available in Wikipedia.|