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Old fertility science is still painfully relevant for today's women

22 July 2013
By Dr Archana Vasireddy and Professor Susan Bewley
Specialty doctor in Obstetrics and Gynaecology, London Deanery (Dr Vasireddy) and Professor of Complex Obstetrics, Women's Health Academic Centre, King's Health Partners, London (Professor Bewley)
Appeared in BioNews 714

As obstetrician-gynaecologists, we should have been excited by Jean Twenge's article 'How long can you wait to have a baby?', published in last week's Observer. She is an American psychologist who purports to 'educate' women about fertility and age, yet criticises the science used to inform them as outdated and alarmist. The science is clear: most women, even in their late 30's, will succeed in having children, but many will face more infertility, miscarriage and complicated pregnancies. Twenge, extrapolating from her own anxieties and successful natural conception of three healthy children, whitewashes the very real problems we see every day with seemingly little empathy for those who suffer in pained silence.

All the eggs a woman will ever have are formed while she herself is in her mother's womb. They fall in number, with only the tiniest proportion making it to ovulation, and diminish in quality as they age over the decades. At birth, girls have already lost most of their eggs but have approximately one million left. At menarche (first period) they have about 250,000 eggs, and these continue to decline biexponentially; the slow steady decline from birth later accelerates from 35 years of age to menopause.

We know this from a huge range of biological, historical and social science data. Twenge argues that much human fertility data is irrelevant as it comes from a time before 'antibiotics and electricity'. Some recent fertility research models use data collected from a variety of settings, including 17th century French parish registers (1). These historical data from large populations in the pre-contraception era form just one useful piece of the puzzle, illustrating 'natural fertility'.

Finding such large populations not using contraception today would be difficult. In any case, how would electricity and antibiotics improve age-related subfertility and yet fail to impact the host of pregnancy complications still found rising with age nowadays? Twenge encourages us to disregard knowledge, although it would be preposterous to throw out all scientific discoveries made in the time before antibiotics and electricity. All scientific knowledge comes from the past, and is constantly refined. It doesn't become outdated just because it's inconvenient!

Roger Gosden, a renowned expert in ovarian reserve, states that menopause is an inevitable consequence of primary ovarian ageing (an inexorable process), and its timing is quite predictable (2). Unlike the dramatic shifts witnessed in the earlier age of menarche and later age of death, there has been no shift in the age of menopause. It is relatively independent of lifestyle, ethnicity and reproductive history, suggesting a genetic determination.

Women who defer childbearing - whether voluntarily, consciously or not - until later in their reproductive life (i.e. over 35), face multiple risks. Most will 'get away with it', as Twenge illustrates. But problems can arise with conceiving, and in both natural and IVF pregnancies. There is an increase in the risk of miscarriage due to the accumulated genetic abnormalities in eggs. Only a minority of women experience the joy of a live term birth with assisted reproduction technology (ART), and many women are exposed to risks that are not publicised by a profit-driven industry.

Harms can occur as a result of the procedure itself, from pregnancy complications related to age and from IVF-pregnancy complications. These include ovarian hyperstimulation syndrome, miscarriage, ectopic pregnancy, pre-eclampsia, pre-term birth and caesarean section. The risks may be more upsetting, and they multiply in twin and triplet pregnancies (more common in older women after natural or IVF conception). Both old and new science tells us so.

For those women experiencing infertility, early pregnancy loss, failed fertility treatment or complications during pregnancy, Twenge's triumphal personal story might seem rather smug and unkind. The anonymous Jane Everywoman, in 'Cassandra's Prophecy', eloquently and insightfully described her different journey of trying to conceive from the age of 32, first naturally and then with the help of fertility treatments (3). She remained childless at the end of this arduous course and doesn't try to overturn settled biological understanding. Graciously, she wants the next generation to be better prepared.

Young women must be informed that the fertility decline means more than just the 'ticking of a biological clock'. How does Twenge's misinformation and propaganda ensure that women are well informed, from the beginning of their reproductive lives, to understand the facts in a way that helps them make their own life decisions, rather than being lulled and socialised into deferral?

As gynaecologists, we see that fertility treatments are no panacea for the age-related decline in fertility; research models have shown that the gap between desired and achievable children cannot be closed by ART (4). A journalist with a book to sell might dismiss facts lightly, but the truth is that fertility falls over the reproductive years, fertility treatments are less successful in older women and pregnancies are associated with more risk. Other women suffer privately, and obstetricians and gynaecologists will be kept in work helping them. The scientific, educational and media communities should collaborate to give consistent information to young women. Until we properly understand the real economic and social drivers of deferral, the rate of involuntary childlessness is set to increase.

1) Leridon H. Can assisted reproduction technology compensate for the natural decline in fertility with age? A model assessment
Human Reproduction |  17 June 2007
2) Gosden R and Gosden LV. Is ovarian ageing inexorable?
Bewley S, Ledger W, Nickolou D, Kehoe S (eds.) Reproductive Ageing - Chapter 7: 65-73 |  2009
3) Everywoman J. Cassandra's prophecy: why we need to tell the women of the future about age-related fertility decline and 'delayed' childbearing
Reproductive BioMedicine Online |  22 April 2013
4) te Velde E, Habbema D, Leridon H and Eijkemans M. The effect of postponement of first motherhood on permanent involuntary childlessness and total fertility rate in six European countries since the 1970s
Human Reproduction |  18 January 2012
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