Fertility

Fertility is the capability to conceive either naturally or with medical intervention such as in-vitro fertilization. Many factors can affect fertility, including the condition of the sperm, eggs, and reproductive organs and the quality of the embryo. About 10 to 15 percent of couples in the United States are unable to conceive after trying for at least a year, a condition called infertility. For millennia, humans have relied on high fertility rates to perpetuate the species. However, as incomes improved and more women entered the workforce, fertility rates declined. In modern times, high-income countries are seeing an increase in fertility rates while many parts of the world continue to see both high poverty and high fertility rates. Experts say a range of factors likely affect these rates, but global fertility overall continues to decline. Some researchers predict a net-zero population rate late in the twenty-first century.

Background

Before modern advances in medicine, individuals had little control over their fertility. Infant and child mortality rates were high so that fertility was necessary to maintain the population and increase the likelihood that the family and community would survive. Fertile members of society were more likely to pass on their genes to the next generation. As human populations prospered, fertility rates often decreased, but more offspring survived and matured.

The global fertility rate has fallen from five children per woman in 1950 to a 2020 rate of 2.5 children per woman. This decrease has occurred because women have access to contraception and more reliable methods of preventing pregnancy, and women and girls have more educational and employment opportunities. Among earlier generations, as income increased, fertility rates decreased. The same correlation was found as more women entered the workforce. In the twenty-first century, this trend reversed in high-income countries, possibly because these governments and societies support parenthood with such benefits as affordable childcare, greater father participation, and workplace flexibility.

Another factor that researchers say affects societies’ fertility rates is age. Communities in which women attain higher education may see families postpone having children, but older parents are more likely to have difficulty conceiving. A range of biological factors may have an impact on fertility as people age, including the quality and quantity of sperm and egg cells.

Overview

The biological process of conception has great potential to go awry. The female body usually reaches sexual maturity, or puberty, between the ages of eight and thirteen, while boys usually reach puberty between ages ten and fifteen. The female reproductive system involves the cervix, fallopian tubes, ovaries, uterus, and vagina. Girls usually start to menstruate when they reach puberty. The menstrual cycle, which is usually monthly and regulated by hormones, is the process by which the female body prepares for pregnancy. The ovaries release an egg that travels through the fallopian tubes to the uterus. This process, ovulation, usually happens between the eleventh and twenty-first days of the menstrual cycle. The uterine wall thickens during the cycle, but if pregnancy does not occur, the uterus sheds this lining of blood and tissue, which passes through the cervix and exits the body through the vagina. The menstrual cycle is measured from the first day when bleeding begins until the first day of the next cycle of bleeding about four weeks later. The male reproductive system also relies on hormones. The external parts of the male reproductive system include the penis, scrotum, and testicles. The scrota encase the testicles, which contain seminiferous tubules that produce sperm. Internal parts include a tube called the vas deferens, which carries sperm to the urethra. The urethra is the tube inside the penis that carries urine or semen, a fluid containing sperm, out of the body.

Sperm may live up to five days, but eggs dissolve twenty-four hours after leaving the ovary. Pregnancy may occur if sperm fertilize the egg within this time. Individuals can use fertility awareness-based methods (FABM) of family planning to determine approximately when ovulation occurs to maximize or minimize the chances of fertilization taking place. Those trying to conceive should have intercourse one to two days before ovulation, while those seeking to avoid pregnancy should not have unprotected sex in this period.

Many factors, including obesity in women and men, can affect fertility. Age is another factor. For women, who are born with up to two million eggs, being older than thirty-five is associated with infertility. Sperm count and movement decrease with a man’s age; researchers say men older than forty-five may take longer to get a partner pregnant. The risk of miscarriage and fetal death increases with age, too. Researchers say in about one-third of cases of infertility, the problem lies with the woman, while another one-third of cases can be attributed to the man. The remaining one-third of cases are caused by both partners. Some problems women experience include difficulty with ovulation caused by hormone imbalances, blocked fallopian tubes, and problems with the uterus. Common problems men experience are erectile dysfunction and varicocele, or enlargement of the veins in the scrotum. This can cause damage to sperm because the veins heat the testes too much.

Fertility Regulation

Persons may wish to control their fertility to avoid or increase the chances of conception. Individuals can use FABM to recognize when ovulation is occurring. For example, the basal body temperature method involves tracking one’s temperature first thing every morning to recognize a slight increase in body temperature, which is one sign that the body has released an egg. Other methods include the calendar method, ovulation method, and cervical mucous method. Some individuals use fertility monitoring kits, which measure hormone levels to help determine the day of ovulation.

Societies and governments also attempted to regulate fertility. Countries generally hope to see a balance between births and deaths to maintain the numbers of working-age people to maintain the economy. The replacement rate is at least 2.1 average births. Some countries attempt to slow population growth because of concerns about having enough resources. Governments use a variety of methods to slow growth such as ensuring access to reproductive health care and increasing the minimum legal age for marriage. China, the world’s most populous country, instituted a one-child policy for most families to slow population growth in 1980. The policy caused a tremendous imbalance in the male-female population ratio because most families favored male children. Couples who had daughters sometimes killed the infants or abandoned them at orphanages or other locations. Couples that had more than one child faced governmental punishment. Some women were forcibly sterilized or forced to have abortions, and many families were fined. As a result, China has about 3 to 4 percent more males than females and many men have been unable to find women to marry. Even after China ended the one-child policy in 2016, most Chinese families were unwilling to have two or more children because they were concerned about the cost of increasing the size of the family. Many parents, especially mothers, worried that having more children would negatively affect their careers. China was on track to see its population, in particular its workforce, shrink rapidly throughout the twenty-first century.

A range of government policies can affect fertility and birth rates. For example, in the United States, the courts have ruled that pharmacists and others who dispense medication can refuse to fill prescriptions or sell condoms and other over-the-counter methods of birth control if they feel the use of such products is against their beliefs. Such policies can prevent women from being able to control their fertility, especially in rural areas where a woman may have to travel a long distance to access another pharmacy.

Economic Concerns

Political and socioeconomic events can impact fertility. Fertility declined significantly after the 1929 stock market crash that signaled the Great Depression and during and after the recession of 2008. In 2020, as the global COVID-19 pandemic affected communities and economies around the world, the US fertility rate decreased by 17.5 births per month per 100,000 women of reproductive age. Later in the year and into early 2021, during a winter wave of infections, the nation’s overall rate bounced and returned to the pre-pandemic rate of decline. However, researchers said analyzing the data and reaching conclusions as to the reasons for the decline was difficult for many reasons. For example, some states see many people from other countries arrive to give birth, but pandemic restrictions reduced travel for much of the year. Furthermore, a large percentage of pregnancies in the United States are unplanned, so researchers cannot determine what factors are at play in these cases.

Like China, the United States’ birthrate was well below replacement rate in the early 2020s. In 2021 the US birthrate was 1.6, while China’s was 1.3. India, the second-most populous country, had a birthrate at replacement rate. Even countries with high birthrates, such as Nigeria (5.1), had lower birthrates than they saw in 1960 (6.4).

Bibliography

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