Fertility and infertility: Definition and epidemiology

doi:10.1016/j.clinbiochem.2018.03.012

Clinical Biochemistry

Volume 62, December 2018, Pages 2-10

https://doi.org/10.1016/j.clinbiochem.2018.03.012 Get rights and content

Highlights

•
8–12% of reproductive-aged couples worldwide suffer from infertility.
•
Males contribute to 50% of infertility cases.
•
The fertility decline in female already starts around 25–30 years.
•
Some modifiable lifestyle factors can affect fertility.

Abstract

Infertility is a disease characterized by the failure to establish a clinical pregnancy after 12 months of regular and unprotected sexual intercourse. It is estimated to affect between 8 and 12% of reproductive-aged couples worldwide. Males are found to be solely responsible for 20–30% of infertility cases but contribute to 50% of cases overall. Secondary infertility is the most common form of female infertility around the globe, often due to reproductive tract infections. The three major factors influencing the spontaneous probability of conception are the time of unwanted non-conception, the age of the female partner and the disease-related infertility. The chance of becoming spontaneously pregnant declines with the duration before conception. The fertility decline in female 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. The disease-related infertility may affect both genders or be specific to one gender. The factors affecting both genders' fertility are hypogonadotrophic hypogonadism, hyperprolactinemia, disorders of ciliary function, cystic fibrosis, infections, systemic diseases and lifestyle related factors/diseases. Premature ovarian insufficiency, polycystic ovary syndrome, endometriosis, uterine fibroids and endometrial polyps may play a role in female infertility. Male infertility may be due to testicular and post-testicular deficiencies. Semen decline that has been observed over the years, endocrine disrupting chemicals and consanguinity are other factors that may be involved.

Introduction

Fertility is the capacity to establish a clinical pregnancy [1]. The term infertility is used by some clinicians interchangeably with subfertility. Formal definitions are, however, very important for appropriate management of reproductive disorders.

Worldwide >186 million people suffer from infertility, the majority being residents of developing countries [2]. While the most powerful negative predictive factor of fertility is increasing women's age at conception [3], other factors including lifestyle and environmental factors are believed to play an increasing role. Factors influencing fertility will be presented as gender specific or not.

Section snippets

Infertility, subfertility and sterility: what are the differences?

Based on the latest international glossary on infertility and fertility care, infertility is defined as a disease characterized by the failure to establish a clinical pregnancy after 12 months of regular, unprotected sexual intercourse or due to an impairment of a person's capacity to reproduce, either as an individual or with his/her partner. Regular sexual intercourse is an important determinant for the occurrence of pregnancy. According to the latest definition by the WHO, infertility is a

Epidemiology of infertility around the world

The prevalence of infertility in reproductive-aged women has been estimated to be one in every seven couples in the western world and one in every four couples in developing countries. In some regions of the world, including South Asia, some countries of sub-Saharan Africa, the Middle East and North Africa, Central and Eastern Europe and Central Asia infertility rates may reach 30% [5].

Males are found to be solely responsible for 20–30% of infertility cases but contribute to 50% of cases

Impact of infertility on demographics

Fertility, infertility, and more precisely fertility rates as being the average number of live births per woman [1] [10] have an impact on population growth or decline.

World regions differ widely in their demographic trends, with rapid population growth and high fertility rates in the poorest countries, particularly in some countries of sub-Saharan Africa, while population decline, ageing and very low fertility rates are a matter of concern in many developed countries [10].

Fig. 1 shows

Factors that may influence the spontaneous fertility of couples

The three major factors affecting the spontaneous probability of conception are (a) time of unwanted non-conception (b) age of the female partner and (c) disease-related infertility [12]. Semen decline that has been observed over time, endocrine disrupting chemicals and consanguinity are other factors that may be involved.

Conclusion

This report describes current knowledge about the definition and epidemiology of fertility and infertility and presents its main etiological factors on both the female and the male's side.

We expect that this collated evidence can be used as background information for the medical world.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of interests

None.

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ReviewFertility and infertility: Definition and epidemiology

Highlights

Abstract

Introduction

Section snippets

Infertility, subfertility and sterility: what are the differences?

Epidemiology of infertility around the world

Impact of infertility on demographics

Factors that may influence the spontaneous fertility of couples

Conclusion

Funding

Declaration of interests

Fertil. Steril.

Fertil. Steril.

Fertil. Steril.

Fertil. Steril.

J. Adolesc. Health Care

Lancet Infect. Dis.

Infect. Dis. Clin. N. Am.

Obstet. Gynecol.

Fertil. Steril.

Fertil. Steril.

Fertil. Steril.

Fertil. Steril.

Fertil. Steril.

Best Pract. Res. Clin. Obstet. Gynaecol.

Fertil. Steril.

Fertil. Steril.

Fertil. Steril.

Am. J. Obstet. Gynecol.

Reprod. BioMed. Online

Eur. Urol.

Fertil. Steril.

Fertil. Steril.

Lancet

Environ. Toxicol. Pharmacol.

Early Hum. Dev.

Reprod. BioMed. Online

Infertility around the globe: new thinking on gender, reproductive technologies and global movements in the 21st century

Hum. Reprod. Update

Physiological aspects of female fertility: role of the environment, modern lifestyle, and genetics

Physiol. Rev.

European classification of infertility taskforce (ECIT) response to Habbema et al., 'Towards less confusing terminology in reproductive medicine: a proposal'

Hum. Reprod.

National, regional, and global trends in infertility prevalence since 1990: a systematic analysis of 277 health surveys

PLoS Med.

A unique view on male infertility around the globe

Reprod. Biol. Endocrinol.

Infertility and the provision of infertility medical services in developing countries

Hum. Reprod. Update

S.I., Infecundity, infertility, and childlessness in developing countries. DHS Comparative Reports No. 9

Global fertility and population trends

Semin. Reprod. Med.

Population Division, World Population Prospects: The 2012 Revision

Definition and prevalence of subfertility and infertility

Hum. Reprod.

Europe's second demographic transition

Popul Bull

Demographics. Europe's population at a turning point

Science

Too old to have children? Lessons from natural fertility populations

Hum. Reprod.

The variability of female reproductive ageing

Hum. Reprod. Update

Should men and women be encouraged to start childbearing at a younger age?

Expert Rev. Obstet. Gynecol.

Reproduction, smell, and neurodevelopmental disorders: genetic defects in different hypogonadotropic hypogonadal syndromes

Front Endocrinol (Lausanne)

Hyperprolactinemia in men: clinical and biochemical features and response to treatment

Endocrine

Estimated age- and sex-specific incidence and prevalence of dopamine agonist-treated hyperprolactinemia

J. Clin. Endocrinol. Metab.

Prevalence of pituitary adenomas: a community-based, cross-sectional study in Banbury (Oxfordshire, UK)

Clin. Endocrinol.

Primary ciliary dyskinesia: mechanisms and management

Appl. Clin. Genet.

Mutation distribution in expanded screening for cystic fibrosis: making up the balance in a context of ethnic diversity

Clin. Chem.

Cystic fibrosis and fertility

Curr. Opin. Obstet. Gynecol.

Review
Fertility and infertility: Definition and epidemiology