Occurrence of fertility problems presenting to primary care: population-level estimates of clinical burden and socioeconomic inequalities across the UK.

STUDY QUESTION: What are the age-specific incident rates of clinically recorded fertility problems in women aged 15-49 years and how do they vary by socioeconomic group and geographic area.

SUMMARY ANSWER: The incident rate of recorded fertility problems was highest in women age 30-34 years: about 1% of women per annum. Overall rates did not vary by socioeconomic group; however, age-specific rates varied substantially by socioeconomic deprivation quintile; among younger women, deprivation was associated with higher infertility rates.

WHAT IS KNOWN ALREADY AND WHAT THIS PAPER ADDS: The rates of infertility in the UK range from 2 to 26%. Infertility definitions and denominators vary widely, and most current evidence is based on questionnaire studies that are subject to recall, reporting and selection bias. The current paper presents population-based estimates of clinically recorded fertility problems in women of reproductive age and the variation by age and socioeconomic deprivation quintile across different regions of the UK, using a nationally representative cohort of women that is larger than any previous study. Although infertility overall does not vary by socioeconomic status, consultation for fertility problems is closely related to socioeconomic patterns of women's age at first conception, demonstrating that many couples have pre-existing, rather than specifically age-related, infertility.

STUDY DESIGN, SIZE, DURATION: This cohort study used data from The Health Improvement Network, a computerized primary care database of anonymized patient records from general practices across the UK, with prospective health records on over 1.7 million women between 1990 and 2010.

PARTICIPANTS/MATERIALS, SETTING AND METHODS: Our cohort included 1,776,746 women of reproductive age (age 15-49 years) who contributed one or more years of active general practice registration. We estimated rates of new clinically recorded fertility problems in these women using medical records and medications exclusively used to treat infertility. We assessed variation in age-specific incidence by socioeconomic deprivation quintile and geographic area using Poisson regression.

MAIN RESULTS AND THE ROLE OF CHANCE: The rate of incident recorded fertility problems was highest in women in the 30-34 year age group (10.9 per 1000 person-years), which equates to approximately 1% of women per annum in this age group. Lowest rates were in women in the 15-19 and 45-49 year age groups (0.7 and 0.4 per 1000 person-years, respectively). Overall rates did not vary by socioeconomic group, measured using quintiles of the Townsend index. Age-specific rates, however, varied substantially with socioeconomic deprivation quintile (P-value for interaction < 0.0001) such that up to age 25, women with more deprivation had more recorded fertility problems [rate ratio (RR) comparing most to least deprived 5.6, 95% confidence interval (CI) 4.4-7.2 at 15-20 years of age]. This reversed from age 25 to 39, when women with more deprivation had fewer recorded fertility problems (RR 0.6 95% CI 0.5-0.6 at age 30-34). After age 40, there was no socioeconomic gradient in absolute rates.

LIMITATIONS, REASONS FOR CAUTION: This is by far the largest population-based study to estimate clinically recorded fertility problems in women and the first in the UK to assess variation across such a broad age group from 15 to 49 years. Our data, however, did not capture women who experience difficulty in conceiving, but do not consult their general practitioner (GP) regarding fertility problems.

WIDER IMPLICATIONS OF THE FINDINGS: Compared with existing estimates, our measures of the extent and distribution of recorded fertility problems in primary care are more useful for GPs, primary care trusts and policy makers for the planning and delivery of fertility services. We have shown a high burden of infertility with little geographic variation; however, the significant burden in young, more deprived women needs recognition in light of age restrictions for treatment availability for infertility in the UK. Not only does treatment access need to be universal and more equitably allocated across socioeconomic groups, but also more resources are required to reduce fertility problems by targeting modifiable risk factors.

STUDY FUNDING/COMPETING INTEREST(S): There was no direct source of funding for this research work. N.N.D. completed the work as part of an M.Sc., which was funded by Developing Solutions Scholarship provided by the International Office, University of Nottingham. J.W. is supported by a University of Nottingham/National Institute for Health Research (NIHR) Senior Clinical Research Fellowship.

TRIAL REGISTRATION NUMBER: Not applicable.