Fertility is the capability to produce

offspring In biology, offspring are the young creation of living organisms, produced either by a single organism or, in the case of sexual reproduction, two organisms. Collective offspring may be known as a brood or progeny in a more general way. This ca ...

through reproduction following the onset of

sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definit ...

. The

fertility rate The total fertility rate (TFR) of a population is the average number of children that would be born to a woman over her lifetime if: # she were to experience the exact current age-specific fertility rates (ASFRs) through her lifetime # she were ...

is the average number of children born by a female during her lifetime and is quantified demographically. Fertility is addressed when there is a difficulty or an inability to reproduce naturally, which is referred to as infertility. Infertility is widespread, with fertility specialists available all over the world to assist mothers and couples who experience difficulties having a baby. Human fertility depends on factors of nutrition, sexual behaviour,

consanguinity Consanguinity ("blood relation", from Latin '' consanguinitas'') is the characteristic of having a kinship with another person (being descended from a common ancestor). Many jurisdictions have laws prohibiting people who are related by blood fr ...

culture Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups ...

, instinct, endocrinology, timing,

economics Economics () is the social science that studies the production, distribution, and consumption of goods and services. Economics focuses on the behaviour and interactions of economic agents and how economies work. Microeconomics analyzes ...

, personality, way of life, and

emotion Emotions are mental states brought on by neurophysiology, neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or suffering, displeasure. There is currently no scientific ...

s. Fertility differs from

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...

, which is defined as the ''potential'' for reproduction (influenced by

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

production, fertilization and carrying a pregnancy to term). Where a woman or the lack of fertility is infertility while a lack of fecundity would be called sterility.

Demography

In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to produce which is termed

. While fertility can be measured, fecundity cannot be. Demographers measure the fertility rate in a variety of ways, which can be broadly broken into "period" measures and " cohort" measures. "Period" measures refer to a cross-section of the population in one year. "Cohort" data on the other hand, follows the same people over a period of decades. Both period and cohort measures are widely used.

Period measures

Crude birth rate The birth rate for a given period is the total number of live human births per 1,000 population divided by the length of the period in years. The number of live births is normally taken from a universal registration system for births; populati ...

(CBR) - the number of live births in a given year per 1,000 people alive at the middle of that year. One disadvantage of this indicator is that it is influenced by the age structure of the population. * General fertility rate (GFR) - the number of births in a year divided by the number of women aged 15–44, times 1000. It focuses on the potential mothers only, and takes the age distribution into account. * Child-Woman Ratio (CWR) - the ratio of the number of children under 5 to the number of women 15–49, times 1000. It is especially useful in historical data as it does not require counting births. This measure is actually a hybrid, because it involves deaths as well as births. (That is, because of infant mortality some of the births are not included; and because of adult mortality, some of the women who gave birth are not counted either.) * Coale's Index of Fertility - a special device used in historical research

Cohort measures

* Total fertility rate (TFR) - the total number of children a woman would bear during her lifetime if she were to experience the prevailing age-specific fertility rates of women. TFR equals the sum for all age groups of 5 times each ASFR rate. * Gross Reproduction Rate (GRR) - the number of girl babies a synthetic cohort will have. It assumes that all of the baby girls will grow up and live to at least age 50. * Net Reproduction Rate (NRR) - the NRR starts with the GRR and adds the realistic assumption that some of the women will die before age 49; therefore they will not be alive to bear some of the potential babies that were counted in the GRR. NRR is always lower than GRR, but in countries where mortality is very low, almost all the baby girls grow up to be potential mothers, and the NRR is practically the same as GRR. In countries with high mortality, NRR can be as low as 70% of GRR. When NRR = 1.0, each generation of 1000 baby girls grows up and gives birth to exactly 1000 girls. When NRR is less than one, each generation is smaller than the previous one. When NRR is greater than 1 each generation is larger than the one before. NRR is a measure of the long-term future potential for growth, but it usually is different from the current population growth rate.

Social and economic determinants of fertility

A parent's number of children strongly correlates with the number of children that each person in the next generation will eventually have. Factors generally associated with increased fertility include

religiosity In sociology, the concept of religiosity has proven difficult to define. The Oxford English Dictionary suggests: "Religiousness; religious feeling or belief. ..Affected or excessive religiousness". Different scholars have seen this concept as ...

, intention to have children, and maternal support. Factors generally associated with decreased fertility include

wealth Wealth is the abundance of valuable financial assets or physical possessions which can be converted into a form that can be used for transactions. This includes the core meaning as held in the originating Old English word , which is from an I ...

, education, female labor participation,

urban Urban means "related to a city". In that sense, the term may refer to: * Urban area, geographical area distinct from rural areas * Urban culture, the culture of towns and cities Urban may also refer to: General * Urban (name), a list of people ...

residence, cost of housing,

intelligence Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning, emotional knowledge, reasoning, planning, creativity, critical thinking, and problem-solving. More generally, it can be des ...

, increased female age and (to a lesser degree) increased male age. The "Three-step Analysis" of the fertility process was introduced by Kingsley Davis and Judith Blake in 1956 and makes use of three proximate determinants: The economic analysis of fertility is part of

household economics Household economics analyses all the decisions made by a household. These analyses are both at the microeconomic and macroeconomic level. This field analyses the structures of households, the behavior of family members, and their broader influence ...

, a field that has grown out of the

New Home Economics Gary Stanley Becker (; December 2, 1930 – May 3, 2014) was an American economist who received the 1992 Nobel Memorial Prize in Economic Sciences. He was a professor of economics and sociology at the University of Chicago, and was a leader of ...

. Influential economic analyses of fertility include Becker (1960), Mincer (1963), and Easterlin (1969). The latter developed the

Easterlin hypothesis The Easterlin hypothesis (Easterlin 1961, 1969, 1973) states that the positive relationship between income and fertility is dependent on relative income. It is considered the first viable and a still leading explanation for mid-twentieth century ba ...

to account for the Baby Boom.

Bongaarts' model of components of fertility

Bongaarts proposed a model where the total fertility rate of a population can be calculated from four proximate determinants and the total fecundity (TF). The index of marriage (Cm), the index of contraception (Cc), the index of induced abortion (Ca) and the index of postpartum infecundability (Ci). These indices range from 0 to 1. The higher the index, the higher it will make the TFR, for example a population where there are no induced abortions would have a Ca of 1, but a country where everybody used infallible contraception would have a Cc of 0. TFR = TF × Cm × Ci × Ca × Cc These four indices can also be used to calculate the total marital fertility (TMFR) and the total natural fertility (TN). TFR = TMFR × Cm TMFR = TN × Cc × Ca TN = TF × Ci ;Intercourse :The first step is sexual intercourse, and an examination of the average age at first intercourse, the average frequency outside marriage, and the average frequency inside. ; Conception :Certain physical conditions may make it impossible for a woman to conceive. This is called "involuntary infecundity." If the woman has a condition making it possible, but unlikely to conceive, this is termed "subfecundity." Venereal diseases (especially

gonorrhea Gonorrhea, colloquially known as the clap, is a sexually transmitted infection (STI) caused by the bacterium ''Neisseria gonorrhoeae''. Infection may involve the genitals, mouth, or rectum. Infected men may experience pain or burning with u ...

, syphilis, and

chlamydia Chlamydia, or more specifically a chlamydia infection, is a sexually transmitted infection caused by the bacterium '' Chlamydia trachomatis''. Most people who are infected have no symptoms. When symptoms do appear they may occur only several we ...

) are common causes. Nutrition is a factor as well: women with less than 20% body fat may be subfecund, a factor of concern for athletes and people susceptible to

anorexia Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gre ...

. Demographer Ruth Frisch has argued that "It takes 50,000 calories to make a baby". There is also subfecundity in the weeks following childbirth, and this can be prolonged for a year or more through

breastfeeding Breastfeeding, or nursing, is the process by which human breast milk is fed to a child. Breast milk may be from the breast, or may be expressed by hand or pumped and fed to the infant. The World Health Organization (WHO) recommends that br ...

. A furious political debate raged in the 1980s over the ethics of baby food companies marketing infant formula in developing countries. A large industry has developed to deal with subfecundity in women and men. An equally large industry has emerged to provide contraceptive devices designed to prevent conception. Their effectiveness in use varies. On average, 85% of married couples using no contraception will have a pregnancy in one year. The rate drops to the 20% range when using withdrawal, vaginal sponges, or spermicides. (This assumes the partners never forget to use the contraceptive.) The rate drops to only 2 or 3% when using the pill or an IUD, and drops to near 0% for implants and 0% for

tubal ligation Tubal ligation (commonly known as having one's "tubes tied") is a surgical procedure for female sterilization in which the fallopian tubes are permanently blocked, clipped or removed. This prevents the fertilization of eggs by sperm and thus the ...

( sterilization) of the woman, or a

vasectomy Vasectomy, or vasoligation, is an elective surgical procedure for male sterilization or permanent contraception. During the procedure, the male vasa deferentia are cut and tied or sealed so as to prevent sperm from entering into the urethra and ...

for the man. ; Gestation :After a

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...

is conceived, it may or may not survive to birth. "Involuntary fetal mortality" involves natural abortion, miscarriages and stillbirth (a fetus born dead). Human intervention intentionally causing abortion of the fetus is called " therapeutic abortion".

Fertility biology

Women have

hormonal A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required f ...

cycles which determine when they can achieve

pregnancy Pregnancy is the time during which one or more offspring develops (gestation, gestates) inside a woman, woman's uterus (womb). A multiple birth, multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occur ...

. The cycle is approximately twenty-eight days long, with a fertile period of five days per cycle, but can deviate greatly from this norm. Men are fertile continuously, but their

sperm quality Semen quality is a measure of male fertility, a measure of the ability of sperm in semen to accomplish fertilization. Semen quality involves both sperm quantity and quality Cryptorchidism, hypospadias, testicular cancer and poor semen quality ma ...

is affected by their health, frequency of ejaculation, and environmental factors. Fertility declines with age in both sexes. For women, the decline begins around the age of 32, and becomes precipitous at age 37. For men, potency and sperm quality begins to decline around the age of 40. Even if an older couple does manage to conceive a child, the pregnancy will be increasingly difficult for the mother, and carries a higher risk of birth defects and genetic disorders for the child. Pregnancy rates for sexual intercourse are highest when it occurs every 1 or 2 days, or every 2 or 3 days. Studies have found no significant difference between different sex positions and pregnancy rate, as long as it results in ejaculation into the

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

Menstrual cycle

A woman's menstrual cycle begins, as arbitrarily assigned, with menses. Next is the follicular phase where estrogen levels build as an ovum matures (due to the follicular stimulating hormone, or FSH) within the ovary. When estrogen levels peak, it spurs a surge of luteinizing hormone (LH) which completes maturation and enables the ovum to break through the ovary wall. This is ovulation. During the luteal phase following ovulation LH and FSH cause the post-ovulation ovary to develop into the corpus luteum which produces progesterone. The production of progesterone inhibits the LH and FSH hormones which (in a cycle without pregnancy) causes the corpus luteum to atrophy, and menses to begin the cycle again. Peak fertility occurs during just a few days of the cycle: usually two days before and two days after the ovulation date. This fertile window varies from woman to woman, just as the ovulation date often varies from cycle to cycle for the same woman. The

ovule In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the '' integument'', forming its outer layer, the ''nucellus'' (or remnant of the megasporangium), and the ...

is usually capable of being fertilized for up to 48 hours after it is released from the ovary. Sperm survive inside the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

between 48 and 72 hours on average, with the maximum being 120 hours (5 days). These periods and intervals are important factors for couples using the rhythm method of contraception.

Female fertility

The average age of menarche in the United States is about 12.5 years. In postmenarchal girls, about 80% of the cycles are anovulatory (ovulation does not actually take place) in the first year after menarche, 50% in the third and 10% in the sixth year. Menopause occurs during a woman's midlife between ages 48 and 55. During menopause, hormonal production by the ovaries is reduced, eventually causing a permanent cessation of the creation of the uterine lining (period). This is considered the end of the fertile phase of a woman's life. The predicted effect of age on female fertility in women trying to get pregnant, without using fertility drugs or in vitro fertilization:A computer simulation run by Henri Leridon, PhD, an epidemiologist with the French Institute of Health and Medical Research: * * At age 30 ** 75% will conceive ending in a live birth within one year ** 91% will conceive ending in a live birth within four years. * At age 35 ** 66% will conceive ending in a live birth within one year ** 84% will conceive ending in a live birth within four years. * At age 40 ** 44% will conceive ending in a live birth within one year ** 64% will conceive ending in a live birth within four years. Studies of couples trying to conceive have yielded better results: one 2004 study of 770 European women found that 82% of 35- to 39-year-old women conceived within a year, while a study in 2013 of 2,820 Danish women saw 78% of 35- to 40-year-olds conceive within a year. According to an opinion by the Practice Committee of the American Society for Reproductive Medicine, specific coital timing or position, and resting supine after intercourse have no significant impact on fertility. Sperm can be found in the cervical canal seconds after ejaculation, regardless of coital position. The use of fertility drugs and/or invitro 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. Studies since 2004 have shown that mammals may continue to produce new eggs throughout their lives, rather than being born with a finite number as previously thought. Researchers at the Massachusetts General Hospital in Boston say that if eggs are newly created each month in humans, current theories about the aging of the female reproductive system will have to be overhauled, although this is conjecture. 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". Birth defects, especially those involving

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

number and arrangement, also increase with the age of the mother. The March of Dimes reports "At age 25, your risk of having a baby with

Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...

is 1 in 1,340. At age 30, your risk is 1 in 940. At age 35, your risk is 1 in 353. At age 40, your risk is 1 in 85. At age 45, your risk is 1 in 35."

Male fertility

Some research suggests that older males have decreased semen volume,

sperm motility Sperm motility describes the ability of sperm to move properly through the female reproductive tract (internal fertilization) or through water (external fertilization) to reach the egg. Sperm motility can also be thought of as the ''quality'', wh ...

, and impaired sperm morphology. In studies that controlled for female partner's age, comparisons between men under 30 and men over 50 found relative decreases in pregnancy rates between 23% and 38%.

Sperm count A semen analysis (plural: semen analyses), also called seminogram or spermiogram, evaluates certain characteristics of a male's semen and the sperm contained therein. It is done to help evaluate male fertility, whether for those seeking pregna ...

declines with age, with men aged 50–80 years producing sperm at an average rate of 75% compared with men aged 20–50 years and larger differences exist in the number of

seminiferous tubules Seminiferous tubules are located within the testes, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa. Structure The epithelium of the tubule consists of a type of sustentacular cells known ...

in the testes containing 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. Decline in male fertility is influenced by many factors, including lifestyle, environment and psychological factors. Some research suggests increased risks for health problems for children of older fathers, but no clear association has been proven. A large scale study in

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

suggested 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 The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...

, controlling for year of birth, socioeconomic status, and maternal age. Increased paternal age has been suggested to correlate with

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social wit ...

but it is unproven. Australian researchers have found evidence to suggest

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

may cause subtle damage to sperm and prevent a healthy pregnancy. They reported fertilization was 40% less successful when the father was overweight. The

American Fertility Society The American Society for Reproductive Medicine (ASRM) is a nonprofit, multidisciplinary organization for advancement of the science and practice of reproductive medicine. The society has its headquarters in Washington, D.C and its administrati ...

recommends an age limit for sperm donors of 50 years or less, and many fertility clinics in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

will not accept donations from men over 40 or 45 years of age.Age Limit of Sperm Donors in the United Kingdom
Pdf file

Historical trends by country

France

The French pronatalist movement from 1919 to 1945 failed to convince French couples they had a

patriotic Patriotism is the feeling of love, devotion, and sense of attachment to one's country. This attachment can be a combination of many different feelings, language relating to one's own homeland, including ethnic, cultural, political or histor ...

duty to help increase their country's birthrate. Even the government was reluctant in its support to the movement. It was only between 1938 and 1939 that the French government became directly and permanently involved in the pronatalist effort. Although the birthrate started to surge in late 1941, the trend was not sustained. Falling birthrate once again became a major concern among demographers and government officials beginning in the 1970s. In mid-2018, there was a bill introduced to legalize single women and lesbian couples to get fertility treatment. At the beginning of 2020, the Senate approved the bill 160 votes to 116. They are a step closer to legalizing fertility treatments for all women regardless of sexual orientation or marital status. Soon there will be no reason for lesbian couples or single women to travel to be able to start their own family.

United States

From 1800 to 1940, fertility fell in the US. There was a marked decline in fertility in the early 1900s, associated with improved contraceptives, greater access to contraceptives and sexuality information and the "first" sexual revolution in the 1920s.

Post-WWII

After 1940 fertility suddenly started going up again, reaching a new peak in 1957. After 1960, fertility started declining rapidly. In the Baby Boom years (1946–1964), women married earlier and had their babies sooner; the number of children born to mothers after age 35 did not increase.

Sexual revolution

After 1960, new methods of contraception became available, ideal family size fell, from 3 to 2 children. Couples postponed marriage and first births, and they sharply reduced the number of third and fourth births.

Infertility

Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to

full term Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

. There are many biological causes of infertility, including some that medical intervention can treat.

Footnotes

References

* Barrett, Richard E., Donald J. Bogue, and Douglas L. Anderton. ''The Population of the United States'' 3rd Edition (1997) compendium of data * * Coale, Ansley J. and Susan C. Watkins, eds. ''The Decline of Fertility in Europe,'' (1986) * Eversley, D. E. C. ''Social Theories of Fertility and the Malthusian Debate'' (1959
online edition
* Garrett, Eilidh et al. ''Family Size in England and Wales: Place, Class, and Demography, 1891-1911''(2001
online edition
* Grabill, Wilson H.. Clyde V. Kiser, Pascal K. Whelpton. ''The Fertility of American Women'' (1958), influential study at the peak of the Baby Boo
online edition
* GuzmÁn, JosÉ Miguel et al. ''The Fertility Transition in Latin America'' (1996
online edition
* Haines, Michael R. and Richard H. Steckel (eds.), ''A Population History of North America.'' Cambridge University Press, 2000, 752 pp. advanced scholarship * Hawes, Joseph M. and Elizabeth I. Nybakken, eds. ''American Families: a Research Guide and Historical Handbook.'' (Greenwood Press, 1991) * Klein, Herbert S. ''A Population History of the United States.'' Cambridge University Press, 2004. 316 pp * Knox, P. L. et al. ''The United States: A Contemporary Human Geography.'' Longman, 1988. 287 pp. * Kohler, Hans-Peter ''Fertility and Social Interaction: An Economic Perspective'' (2001
online edition
* Leete, Richard. ''Dynamics of Values in Fertility Change'' (1999
online edition
* Lovett, Laura L. ''Conceiving the Future: Pronatalism, Reproduction, and the Family in the United States, 1890–1938,'' (2007) 236 pages; * Mintz Steven and Susan Kellogg. ''Domestic Revolutions: a Social History of American Family Life.'' (1988) * * Population Reference Bureau, ''Population Handbook'' (5th ed. 2004)
online
(5th ed. 2004). * Reed, James. ''From Private Vice to Public Virtue: The Birth Control Movement and American Society Since 1830.'' 1978. * Tarver, James D. ''The Demography of Africa'' (1996
online edition
* Weeks, John R. ''Population: An Introduction to Concepts and Issues'' (10th ed. 2007), standard textbook

Journals

* ''Demography'' �
Scope and links to issue contents & abstracts.
* ''

Journal of Population Economics The ''Journal of Population Economics'' is a quarterly peer-reviewed academic journal that covers research on economic and demographic problems. It is the official journal of the European Society of Population Economics and is published by Springe ...

'' * ''Population and Development Review'' —
Aims and abstract & supplement links.
* ''Population Bulletin'' — Each issue on a
current population topic.
* ''Population Studies'' �
Aims and scope.
* '' Review of Economics of the Household''

External links

Data on fertility trends worldwide {{Authority control