Адамның өрімталдығы және көбею қабілеті

Natural capability to produce offspring
fertility in humans

Fertility is the ability to conceive a child. The fertility rate is the average number of children born during an individual's lifetime and is quantified demographically. Conversely, infertility is the difficulty or inability to reproduce naturally. In general, infertility is defined as not being able to conceive a child after one year (or longer) of unprotected sex. Because infertility is widespread, fertility specialists all over the world assist persons and couples who experience difficulties conceiving a baby. Fertility is an issue for people of both sexes. According to the Centers for Disease Control and Prevention, in 35% of couples who cannot conceive, the cause can be attributed to factors on both the female and male side. lifestyle, and emotions. Fertility differs from fecundity, which is defined as the biological capacity to reproduce irrespective of intention for conception. Fecundity can be explained by gamete production, fertilization, and carrying a pregnancy to term. The antithesis of fertility is infertility, while the antithesis of fecundity is sterility.

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

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.

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, intention to have children, and maternal support. Factors generally associated with decreased fertility include wealth, education, female labor participation, urban residence, cost of housing, intelligence, 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, a field that has grown out of the New Home Economics. Influential economic analyses of fertility include Becker (1960), Mincer (1963), and Easterlin (1969). The latter developed the Easterlin hypothesis to account for the Baby Boom.

Women have hormonal cycles which determine when they can achieve pregnancy. 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 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.

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

Some research suggests that older males have decreased semen volume, sperm motility, 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%. 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 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, controlling for year of birth, socioeconomic status, and maternal age. Increased paternal age has been suggested to correlate with schizophrenia but it is unproven. Australian researchers have found evidence to suggest obesity 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 recommends an age limit for sperm donors of 50 years or less, and many fertility clinics in the United Kingdom will not accept donations from men over 40 or 45 years of age.

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

South Korea has the lowest fertility rate in the world at 0.78. A variety of explanations have been proposed, ranging from investment in education to birth control, abortion, a decline in the marriage rate, divorce, female participation in the labor force, and the 1997 Asian financial crisis. After being legal from the 1960s to the 1980s, abortion was again made illegal in South Korea in the early 2000s in an attempt to reverse the declining fertility rate.

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.

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.

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.

Studies have been conducted to identify external factors that impact fertility rates and embryo development. Two main factors were determined to have the greatest impact, eating habits and lifestyle choices. Eating choices include quality, types and frequency of food intake. Grains, fruits and vegetables have a positive influence on embryo quality. Alcohol intake, cigarette and marijuana use all have a detrimental impact on female reproductive function. During embryogenesis, the DNA structure and expression can be heavily influenced by lifestyle, nutrition and environmental toxins.

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