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Fertility

Age related decline in fertility affects both sexes, say Alexandra van der Meer and colleagues

What do the literary and film characters Bridget Jones and James Bond have in common? According to research, they may well share the phenomenon of the ticking biological clock. Is the question of when to have our children relevant to both sexes? While there are a number of mature medical students, some of whom will have started or completed their family, most medical students have yet to start. Pursuing a demanding career in medicine may delay any consideration of planning when to fit this in, let alone advancing the plan.

Both men and women should be concerned about their biological clocks. While most people would recognise that Bridget Jones is likely to suffer the experience of a biological clock, many would question whether this could be true of James Bond. Why is it that we are never shown the children and angry ex-lovers hounding Bond for child maintenance payments? Is it possible that this man, generally depicted in his late 30s or early 40s, has poorer sperm and some age related fertility issues?

Female fertility

Back to Bridget: Surely continuing to smoke, drink, and go on crash diets does not help her chances of conception? It is no secret that women are having children later in life. In 2004, for the first time, women in their early 30s overtook the 25-29 year old category for the highest fertility rates of all age groups (fig 1). Figure 2 shows the dramatic shift in the demography of births over the past 40 years.^{1 2}

Fig 1 Female age specific fertility rates, 1997-2007¹ (2007 data provisional because based on the 2006 based population projections for 2007)

Fig 2 Number of births by maternal age in England and Wales, 1974-2004

Many young women are busy pursuing their careers, which seem to have overtaken or displaced their desire to have children. This is particularly true of women with degree qualifications, who are much more likely to remain childless or to have just one child than those with no or lower qualifications.² Those who put off having children until their 30s or 40s may then face difficulties in getting pregnant. Less than half of women aged 30-39 years who intended to have a child succeeded in six years, according to data from the British Household Panel Study.²

Increasing age increases the risk of infertility, miscarriage, stillbirth, and ectopic pregnancy (fig 3).³ Accompanying this are the well established risks to the child’s health—for example, from prematurity or the increased risk of trisomy 21. While it has seemed controversial at times, it is not difficult to draw the conclusion that it is biologically best to start trying for children before reaching one’s 30s.³

Fig 3 Fertility and miscarriage rates as a function of maternal age. Miscarriage is defined as spontaneous pregnancy loss before the 20th week of gestation. Reproduced with permission⁴

Doctors are particularly prone to delaying childbearing. As healthcare professionals we have an opportunity to be better informed and obtain insight on the possible future difficulties that we may face regarding our health. However, we can still fall into the trap of false security by hoping “it will not happen to me”; all women’s fertility is affected by age. Although assisted reproductive techniques can bring great joy to a small proportion of infertile couples, they have low success rates (particularly in women over 35) and should not be relied on. Assisted reproduction cannot be considered an adequate fallback plan. According to data from the Human Fertilisation and Embryology Authority, the success rates of in vitro fertilisation and intracytoplasmic sperm injection fall as the woman ages: the percentage live birth rates for all treatment cycles with these techniques using fresh embryos are 31% at 30 years, 24.3% at 35 years, 12.5% at 40 years, 1.3% at 45 years.⁵ However, a career in medicine need not mean postponing or excluding motherhood.

Male fertility

What, we hear men cry, James Bond, the most successful womaniser in fictional history, infertile because of his age?

Men, like women, are fathering children later in life. The fertility rates for men aged 20-29 years is generally falling, with men aged 30-34 years having the highest fertility rate in 2004.⁶ The percentage contribution to total fertility rate by men has an older age distribution than for women—for example, fertility of men over 40 years contributes 12% of the total fertility rate, compared with 3% of women in same age group.⁶ This may lead you to think that a man in his 40s is still fertile and has his virility intact. However, according to data from the Human Fertilisation and Embryology Authority the number of in vitro fertilisation cycles being performed because of male factor infertility is rising.⁵

Some controversy surrounds research into age and its effect on male fertility as it is often difficult to separate age of the female partner and other factors from confounding evidence. At the 2008 European Society for Human Reproduction and Embryology conference, research was presented that followed 12 236 couples through 21 239 intrauterine inseminations where the partner’s sperm was used each time. Most couples were having treatment as a result of male factor infertility. The researchers analysed sperm count, motility, and morphology and were able to separate the male and female factors related to each pregnancy. Paternal age of over 40 years was found to increase miscarriage rates and to have a negative effect on pregnancy rates.⁷

Studies have shown that semen quality declines with age; both the genetic and physical characteristics of the sperm are affected. Also, semen volume decreases with age, as do motility and morphology.⁸ It may be expected that as male germ cells divide continuously throughout life, mutations producing genetic abnormalities increase as a man ages. Coupled with a reduced rate of apoptosis during spermatogenesis, this results in a higher chance of error. Rates of genetic diseases with both simple (for example, achondroplasia) and complex (for example, schizophrenia) inheritance are increased in populations with older fathers.⁹

Balancing career with family

It is understandable that doctors are more prone to postponing childbearing, given the length of education, intensity of training, and level of competition. However, a successful career and an enjoyable family life need not be mutually exclusive. As more women enter and progress through medical training, the demand for the time and opportunity to have a family has risen. The health service risks losing young doctors if this cannot be catered for. It is now a statutory requirement to provide up to 12 months maternity leave,¹⁰ but what happens after that year? In 2000 a working party was established of representatives from the BMA, the Department of Health, the royal colleges, and the postgraduate medical deaneries to investigate flexible training for both men and women within the NHS. They made a number of recommendations in 2003, including the need for flexible posts to be available to all, the requirement of published detailed guidance, and the provision of better childcare.¹¹ Although more trusts are providing flexible training posts, some difficulties have arisen regarding their funding, but as the demand for such positions increases, the problems will be solved. We believe that it should be possible to have the best of both worlds and enjoy a challenging career with a flourishing family life (accepting that raising a child is a challenge in itself).

Competing interests: None declared.

Provenance and peer review: Not commissioned; externally peer reviewed.

See “Male infertility,” Student BMJ 2008;16:368-9, http://student.bmj.com/issues/08/10/education/368.php.

Alexandra van der Meer fifth year medical student ¹University of Liverpool
alexvandermeer@doctors.org.uk
Hannah Turton fourth year medical student ²King’s College, London
Susan Bewley consultant obstetrician ³Guy’s and St Thomas’ NHS Foundation Trust, London
Student BMJ 2009;17:001-036-ISSN 0966-6494 | January 2009

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