Fertility is the biological capacity of an individual or couple to produce offspring through reproduction. Fertility is a person’s ability to conceive children, encompassing the complex physiological processes that enable conception, pregnancy, and childbirth. At the population level, fertility is measured through metrics such as the total fertility rate (TFR), which represents the average number of children that are born to a woman over her lifetime, assuming she experiences current age-specific fertility rates throughout her reproductive years.
Fertility
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| Category | Reproductive Health, Demography, Biology |
| Research Fields | Reproductive Medicine, Demography, Endocrinology |
| Also known as: | Fecundity, reproductive capacity, childbearing ability |
| Pronunciation: | fur-TIL-i-tee |
| Global TFR (2023): | 2.3 births per woman |
| Replacement level: | 2.1 births per woman (developed countries) |
| Historical range: | 4.5-7.5 children per woman (pre-industrial) |
| Infertility prevalence: | 8-12% of couples globally |
| Peak fertility age: | Early 20s to early 30s |
| Sources: | WHO, Clinical Medicine Insights, CDC Reproductive Health, StatPearls |
Globally, the total fertility rate was 2.3 children per woman in 2023, much lower than in the past; in the 1950s, it was more than twice as high: 4.9. The fertility rate is the average number of children born to a woman in her lifetime, which has gone from 4.84 in 1950 to 2.23 in 2021 and will continue to drop to 1.59 by 2100. This dramatic decline represents one of the most significant demographic transformations in human history.
Understanding fertility involves both individual reproductive health and broader population dynamics. Infertility is defined as the failure to achieve a pregnancy after 12 months or more of regular unprotected sexual intercourse, affecting between 8 and 12% of reproductive-aged couples worldwide. Comprehensive fertility awareness encompasses knowledge of reproductive cycles, factors affecting conception, and available interventions for fertility challenges.
History
Prehistoric Era: Natural Fertility Patterns
From around 10,000 BC to the beginning of the Industrial Revolution, fertility rates around the world were high by 21st-century standards, ranging from 4.5 to 7.5 children per woman. Early human societies developed various cultural practices and beliefs around fertility, with reproduction being essential for survival and continuation of communities.
Ancient Civilizations: Religious and Cultural Frameworks
Ancient civilizations developed complex religious and cultural frameworks around fertility, reproduction, and family formation. Fertility goddesses and rituals were central to many cultures, reflecting the vital importance of reproduction for agricultural societies and community survival.
1800s: Industrial Revolution and Demographic Transition
The onset of the Industrial Revolution around the year 1800 brought about what has come to be called the demographic transition. Urbanization, improved living conditions, and changing economic structures began to influence family size decisions and reproductive patterns in developed nations.
Early 1900s: Scientific Understanding of Reproduction
The early 20th century saw significant advances in understanding reproductive physiology, including the discovery of hormones and their role in the menstrual cycle. This period marked the beginning of scientific approaches to understanding and managing fertility.
1960s: Contraceptive Revolution
The development and widespread availability of effective contraception, particularly the birth control pill, gave individuals unprecedented control over their fertility. After the 1960s, when the global average TFR was still 5, it has dropped steadily to less than half that number.
1978: First IVF Baby
The birth of Louise Brown, the first baby conceived through in vitro fertilization, marked a revolutionary moment in fertility treatment. This breakthrough opened new possibilities for treating infertility and understanding reproductive processes.
1990s-2000s: Advanced Reproductive Technologies
The development of intracytoplasmic sperm injection (ICSI), preimplantation genetic testing, and egg freezing expanded treatment options for infertility and enabled fertility preservation for various medical and social reasons.
2010s-Present: Personalized Reproductive Medicine
Recent advances include genetic testing, personalized treatment protocols, and emerging technologies like artificial gametes. By 2050, over three-quarters of countries will not have high enough fertility rates to sustain population size over time, increasing to 97% of countries by 2100.
Biological Mechanisms
Female Reproductive Cycle
To get pregnant, a woman’s body must release an egg from one of her ovaries, a man’s sperm must join with the egg along the way (fertilize), the fertilized egg must go through a fallopian tube toward the uterus, and the embryo must attach to the inside of the uterus (implantation). The menstrual cycle typically lasts 28 days, with ovulation occurring around day 14 in regular cycles.
Male Reproductive Function
Male fertility depends on the production of healthy sperm in adequate quantities, proper sperm function including motility and morphology, and successful delivery of sperm through the reproductive tract. In the male reproductive system, infertility is most commonly caused by problems in the ejection of semen, absence or low levels of sperm, or abnormal shape and movement of the sperm.
Hormonal Regulation
Fertility in both sexes is regulated by complex hormonal interactions involving the hypothalamic-pituitary-gonadal axis. Key hormones include gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and sex steroids (estrogen, progesterone, testosterone).
Age and Fertility
The fertility decline in females already starts around 25-30 years of age and the median age at last birth is 40-41 years in most studied populations experiencing natural fertility. A 25-year-old female has a 25% to 30% chance of getting pregnant each menstrual cycle. By the time you reach 40, your chances are less than 5% each cycle.
Global Fertility Patterns
Regional Variations
In 2023, the total fertility rate was highest in countries in Africa and central Asia, where most countries had a total fertility rate between 3 to 7 births per woman, and lowest in countries in East Asia, where most countries had a total fertility rate below 1. As of 2023, the total fertility rate varied widely across the world, from 0.7 in South Korea, to 6.1 in Niger.
Developed vs. Developing Countries
Fertility tends to be inversely correlated with levels of economic development. Historically, developed countries have significantly lower fertility rates, generally correlated with greater wealth, education, urbanization, and other factors. This pattern reflects the demographic transition experienced as societies modernize.
Replacement Level Fertility
Replacement fertility is the total fertility rate at which women give birth to enough babies to sustain population levels. In 2003, the replacement fertility rate was 2.1 births per female for most developed countries but could be as high as 3.5 in undeveloped countries because of higher mortality rates.
Future Projections
The United Nations predicts that global fertility will continue to decline for the remainder of this century and reach a below-replacement level of 1.8 by 2100, and that world population will peak in 2084. The number of countries and territories below replacement level is predicted to increase to 198 of 204 (97%) by 2100.
Factors Affecting Fertility
Age-Related Factors
Female fertility begins to decline in the late 20s and early 30s, with more rapid decline after age 35. Male fertility also decreases with age, though less dramatically than female fertility. Advanced paternal age is associated with increased risk of genetic abnormalities and certain health conditions in offspring.
Lifestyle Factors
Smoking, excessive alcohol consumption, drug use, obesity, extreme weight loss, excessive exercise, and stress can all negatively impact fertility in both men and women. The factors affecting both genders’ fertility include lifestyle related factors/diseases.
Environmental Factors
Exposure to environmental toxins, endocrine disruptors, radiation, and certain chemicals can affect reproductive function. Endocrine disrupting chemicals are factors that may be involved in fertility decline. Occupational exposures and air pollution may also impact fertility outcomes.
Medical Conditions
The disease-related infertility may affect both genders including hypogonadotrophic hypogonadism, hyperprolactinemia, disorders of ciliary function, cystic fibrosis, infections, and systemic diseases. Premature ovarian insufficiency, polycystic ovary syndrome, endometriosis, uterine fibroids and endometrial polyps may play a role in female infertility.
Infertility: Causes and Treatment
Definition and Prevalence
Infertility is a disease of the male or female reproductive system defined by the failure to achieve a pregnancy after 12 months or more of regular unprotected sexual intercourse. About 9% of men and about 11% of women of reproductive age in the United States have experienced fertility problems.
Gender Distribution
About one-third of infertility cases are caused by fertility problems in women and another one-third of infertility cases are due to fertility problems in men. The other cases are caused by a mixture of male and female problems or by problems that cannot be determined. Males are found to be solely responsible for 20-30% of infertility cases but contribute to 50% of cases overall.
Female Infertility Causes
Most cases of female infertility are caused by problems with ovulation. Ovulation problems can be caused by hormone imbalances from a variety of causes. Although less common, blocked fallopian tubes can also cause female infertility. In the female reproductive system, infertility may be caused by abnormalities of the ovaries, uterus, fallopian tubes, and the endocrine system, among others.
Male Infertility Causes
Male infertility may be due to testicular and post-testicular deficiencies. Common causes include low sperm count, poor sperm motility, abnormal sperm morphology, blockages in the reproductive tract, and hormonal imbalances affecting sperm production.
Treatment Options
Treatment options for infertility may include timed intercourse, medications, intrauterine insemination, surgery, or assisted reproductive technology. Treatment of infertility often involves in-vitro fertilization (IVF) and other types of medically assisted reproduction. Success rates vary depending on age, cause of infertility, and specific treatment approach.
Fertility Awareness and Family Planning
Natural Family Planning
To chart her menstrual cycle, a woman can simply record the day her period starts and when it ends. Over time, this tracking will help a woman see what the typical amount of time between periods is, which can help her predict when her next period will start. Fertility awareness methods help couples understand natural fertility patterns for both achieving and avoiding pregnancy.
Modern Fertility Tracking
Technology has enhanced fertility awareness through smartphone apps, wearable devices, and home monitoring tools that track various fertility indicators including basal body temperature, cervical mucus, and hormone levels. Advanced fertility tracking technologies provide real-time insights into reproductive cycles.
Preconception Health
Optimizing health before conception includes maintaining healthy weight, taking folic acid supplements, avoiding harmful substances, managing chronic conditions, and ensuring up-to-date vaccinations. Preconception counseling helps couples prepare for healthy pregnancies.
Social and Economic Implications
Population Demographics
A shrinking population poses great economic and societal challenges, but it also has environmental benefits. A smaller global population could alleviate strain on global resources and reduce carbon emissions. However, aging populations create challenges for healthcare systems and economic productivity.
Women’s Rights and Education
Increased opportunities for women in education and employment and better access to contraception and reproductive health services contribute to declining fertility rates. It is well established that nations with strong women’s rights are more likely to have better health outcomes and faster economic growth.
Policy Responses
Social policies to improve birth rates such as enhanced parental leave, free childcare, financial incentives, and extra employment rights may provide a small boost to fertility rates, but most countries will remain below replacement levels. There is very real concern that some countries might justify more Draconian measures that limit reproductive rights.
Cultural and Religious Perspectives
Religious Views on Fertility
Different religious traditions have varying perspectives on fertility, contraception, and assisted reproduction. Some emphasize procreation as a divine mandate, while others focus on responsible parenthood and family planning. These beliefs significantly influence individual and societal approaches to fertility management.
Cultural Variations
Cultural attitudes toward family size, gender preferences, and reproductive timing vary widely across societies. Some cultures value large families as economic assets or sources of social status, while others prioritize smaller families and individual achievement.
Stigma and Social Support
In some settings, fear of infertility can deter women and men from using contraception if they feel socially pressured to prove their fertility at an early age because of a high social value of childbearing. Addressing fertility-related stigma requires comprehensive education and supportive healthcare approaches.
Research Landscape
Emerging Technologies
Research continues on artificial gametes, uterine transplantation, and genetic editing technologies that could revolutionize fertility treatment. Cutting-edge reproductive technologies may soon offer new solutions for previously untreatable fertility conditions.
Personalized Medicine
Advances in genetics and biomarkers are enabling more personalized approaches to fertility treatment, including customized hormone protocols and genetic screening for optimal treatment selection. Precision medicine promises to improve success rates while reducing treatment burden.
Global Health Initiatives
WHO is committed to addressing infertility and fertility care by collaborating with partners to conduct global epidemiological research, engaging in policy dialogue, supporting data generation, and developing guidelines on prevention, diagnosis and treatment.
Frequently Asked Questions
What is the difference between fertility and fecundity?
Fertility refers to actual reproductive performance (number of children born), while fecundity refers to biological capacity to reproduce. A person may be fecund (biologically capable) but choose to have fewer children than their maximum reproductive potential.
At what age does fertility start declining?
Female fertility begins declining in the late 20s, with more noticeable decline after age 30 and significant decline after age 35. Male fertility also decreases with age but less dramatically, typically beginning in the 40s with gradual decline thereafter.
How long should couples try before seeking fertility help?
Generally, couples under 35 should seek evaluation after 12 months of unprotected intercourse without conception. Those 35-39 should seek help after 6 months, and those over 40 should consult a healthcare provider after 3-6 months of trying.
Can lifestyle changes improve fertility?
Yes, maintaining healthy weight, regular exercise, balanced nutrition, avoiding smoking and excessive alcohol, managing stress, and limiting exposure to environmental toxins can all positively impact fertility in both men and women.
What are the success rates of fertility treatments?
Success rates vary by age, diagnosis, and treatment type. IVF success rates range from about 40% per cycle for women under 35 to less than 10% for women over 42. Success is typically measured by live birth rates per treatment cycle.
Is male fertility testing important?
Yes, male factors contribute to about 50% of infertility cases. Initial male fertility evaluation typically includes semen analysis to assess sperm count, motility, and morphology, along with hormone testing when indicated.
How does stress affect fecundity?
Chronic stress can disrupt hormonal balance and interfere with ovulation and sperm production. While stress alone rarely causes infertility, managing stress through relaxation techniques, counseling, or lifestyle changes may improve fertility outcomes and overall well-being during treatment.