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 malerole is better known. Infertilityis 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.
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, seedsor vegetables.
fertility rateis a demographic measure of the number of childrenper woman. Although it has been until recently considered to be a fairly reliable indicator of populationgrowth, it is no longer so in much of Asia. Due to selective abortionand 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, Myanmar, and Korea.
Both women and men have hormonal cycles which determine both when a woman can achieve
pregnancyand 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 qualitydips occasionally, which scientists guess is in relation to their internal cycle.
Furthermore, age also plays a role, especially for women.
Although women can become pregnant at any time during their
menstrual cycle, peak fertility occurs during just a few days of the cycle: usually two days before and two days after the ovulation date [http://www.duofertility.com/en/my-body/my-cycle/my-fertile-period.html] . This fertile window, varies between from woman to woman, just like the ovulation date often varies from cycle to cycle for the same woman [cite journal |author=Creinin MD, Keverline S, Meyn LA |title=How regular is regular? An analysis of menstrual cycle regularity |journal=Contraception |volume=70 |issue=4 |pages=289–92 |year=2004 |month=Oct |pmid=15451332 |doi=10.1016/j.contraception.2004.04.012 |url=] . The ovuleis usually fertilisable for up to 48 hours after it is released from the ovary. However, spermcan survive inside the uterusbetween 48 to 72 hours on average, with the maximum being 120 hours (5 days).
The average age of
menarchein the United States is about 12.5 years. [cite journal |author=Anderson SE, Dallal GE, Must A |title=Relative weight and race influence average age at menarche: results from two nationally representative surveys of US girls studied 25 years apart |journal=Pediatrics |volume=111 |issue=4 Pt 1 |pages=844–50 |year=2003 |month=Apr |pmid=12671122 |doi= |url=http://pediatrics.aappublications.org/cgi/content/full/111/4/844?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&searchid=1&FIRSTINDEX=0&minscore=5000&resourcetype=HWCIT ] In postmenarchal girls, about 80% of the cycles were anovulatory in the first year after menarche, 50% in the third and 10% in the sixth year. [cite journal |author=Apter D |title=Serum steroids and pituitary hormones in female puberty: a partly longitudinal study |journal=Clin. Endocrinol. (Oxf) |volume=12 |issue=2 |pages=107–20 |year=1980 |month=Feb |pmid=6249519 |doi= |url=] [cite journal |author=Apter D |title=Serum steroids and pituitary hormones in female puberty: a partly longitudinal study |journal=Clin. Endocrinol. (Oxf) |volume=12 |issue=2 |pages=107–20 |year=1980 |month=Feb |pmid=6249519 |doi=10.1111/j.1365-2265.1980.tb02125.x |url=http://www3.interscience.wiley.com/journal/119590594/abstract] Women's fertility peaks around the age of 19-24, and often declines after 30. With a rise in women postponing pregnancy,http://findarticles.com/p/articles/mi_m1077/is_1_62/ai_n16807720 "Late-in-life Pregnancy"] this can create an infertilityproblem. 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. [cite web | title=Fertility Treatment Less Successful After 35 | work=WebMD | url=http://www.webmd.com/content/article/89/100183.htm | accessmonthday=July 4 | accessyear=2006]
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". [cite web | title=Pregnancy After 35
work=March of Dimes | url=http://www.marchofdimes.com/professionals/14332_1155.asp | accessmonthday=May 21 | accessyear=2008]
Birth defects, especially those involving
chromosomenumber 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." [cite web | title=The sterility tax can be reestablished in Russia | url=http://russia-ic.com/business_law/in_depth/253/
accessmonthday=September 22 | accessyear=2006]
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. [cite web|title=Spanish woman ' is oldest mother'|date=|30 December, 2006|accessdate=2006-12-30|url=http://news.bbc.co.uk/2/hi/health/6220523.stm|publisher=BBC News]
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. [ [http://fertilitytesting.co.uk/female_fertility_tests.htmlFertility Testing] (Female Fertility Testing)]
Male fertility and age
Erectile dysfunctionincreases with age, [http://www.infertile.com/inthenew/sci/maleage.htm Effect of Age on Male Fertility] Seminars in Reproductive Endocrinology. Volume, Number 3, August 1991. Sherman J. Silber, M.D.] 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. However, evidence suggests that increased male age is associated with a decline in semen volume, sperm motility, and sperm morphology.cite journal |author=Kidd SA, Eskenazi B, Wyrobek AJ |title=Effects of male age on semen quality and fertility: a review of the literature |journal=Fertil. Steril. |volume=75 |issue=2 |pages=237–48 |year=2001 |month=Feb |pmid=11172821 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/S0015-0282(00)01679-4] In studies that controlled for female age, comparisons between men under 30 and men over 50 found relative decreases in pregnancy rates between 23% and 38%.
Cause of decline
Sperm countdeclines 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 tubulesin the testescontain 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.
Recent research has suggested increased risks for health problems for children of older fathers. A large scale Isreali study found that the children of men 40 or older were 5.75 times more likely than children of men under 30 to have an autism spectrum disorder, controlling for year of birth, socioeconomic status, and maternal age. [cite journal |author=Reichenberg A, Gross R, Weiser M, "et al" |title=Advancing paternal age and autism |journal=Arch. Gen. Psychiatry |volume=63 |issue=9 |pages=1026–32 |year=2006 |month=Sep |pmid=16953005 |doi=10.1001/archpsyc.63.9.1026 |url=http://archpsyc.ama-assn.org/cgi/content/abstract/63/9/1026] Increased paternal age has also been correlated to schizophrenia in numerous studies. [cite journal |author=Malaspina D, Harlap S, Fennig S, "et al" |title=Advancing paternal age and the risk of schizophrenia |journal=Arch. Gen. Psychiatry |volume=58 |issue=4 |pages=361–7 |year=2001 |month=Apr |pmid=11296097 |doi= |url=http://archpsyc.ama-assn.org/cgi/pmidlookup?view=long&pmid=11296097] [cite journal |author=Sipos A, Rasmussen F, Harrison G, "et al" |title=Paternal age and schizophrenia: a population based cohort study |journal=BMJ |volume=329 |issue=7474 |pages=1070 |year=2004 |month=Nov |pmid=15501901 |pmc=526116 |doi=10.1136/bmj.38243.672396.55 |url=] [cite journal |author=Malaspina D, Corcoran C, Fahim C, "et al" |title=Paternal age and sporadic schizophrenia: evidence for de novo mutations |journal=Am. J. Med. Genet. |volume=114 |issue=3 |pages=299–303 |year=2002 |month=Apr |pmid=11920852 |doi= |url=http://dx.doi.org/10.1002/ajmg.1701]
The American Fertility Society recommends an age limit for sperm donors of 50 years or less. [cite journal |author=Plas E, Berger P, Hermann M, Pflüger H |title=Effects of aging on male fertility? |journal=Exp. Gerontol. |volume=35 |issue=5 |pages=543–51 |year=2000 |month=Aug |pmid=10978677 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/S0531-5565(00)00120-0] Many fertility clinics in the United Kingdom will not accept donations from men over 40 or 45. [http://www.spermdonorforum.com/documents/sperm_donor_clinics_uk_2007.pdf] Many women are using a take-home baby rate calculator to estimate their chances of success following
in vitro fertilisation. [http://www.formyodds.com]
Fertility and intelligence
Total fertility rate
* [http://www.preventinfertility.info International Agency for Prevention of Infertility (IAPI) ]
*cite journal |author=Bock J |title=Introduction: evolutionary theory and the search for a unified theory of fertility |journal=Am. J. Hum. Biol. |volume=14 |issue=2 |pages=145–8 |year=2002 |pmid=11891930 |doi=10.1002/ajhb.10039 |url=http://anthro.fullerton.edu/jbock/BockIntroAJHB.pdf
*cite journal |author=Jones C |title=Ethical and legal conundrums of postmodern procreation |journal=Int J Gynaecol Obstet |volume=100 |issue=3 |pages=208–10 |year=2008 |month=Mar |pmid=18062970 |doi=10.1016/j.ijgo.2007.09.031 |url=
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