When does the Biological Clock of a Woman Start Ticking

As contemporary women become more committed to professional advancement and even perhaps a single’s lifestyle, a phrase that keeps coming up in related discussions is the ticking of the biological clock. Does this really refer to the inexorable march of time on a woman’s body or is it yet another phrase coined to keep women  firmly in their place - as in the home and nursery. And if it is at all a scientific fact, when indeed does this clock start ticking for women.

What is the cause ?

In popular usage, the ticking away of a woman’s biological clock means that she is getting too old to have a baby. Doctors are not yet certain of the exact causes of infertility in women. But it is believed the quality of a woman's eggs is a crucial factor. A woman's egg supply is set before birth, declines dramatically even before she's out of the womb, and by the time she reaches menopause, most of her eggs are gone. In addition to that, a woman's left not just with fewer and fewer eggs as she ages, but with a higher concentration of abnormal ones. It is generally believed that female fertility begins to drop in the mid-30s because the quality of eggs a woman is born with begins to deteriorate throughout her 20s and 30s. One probable reason why this happens is that ability to repair DNA inside their egg cells may become impaired, leading to accumulating damage to the eggs that causes them to die off more rapidly¹.

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What do numbers say?

But researchers now believe that a woman's biological clock may start ticking years earlier. Scientists at the National Institute of Environmental Health Sciences in North Carolina and the University of Padua in Italy² studied 872 healthy couples and found that while 19 to 26-year-olds have a 50 per cent chance of conceiving two days before ovulation - a woman's most fertile time, that rate dropped to 40 per cent for those aged 27 to 34. After 35, the women studied had only a 30 per cent chance of falling pregnant in any given month. This research is the first to indicate that female fertility declines before the age of 30. However doctors involved with the research said the older women studied were not less able to conceive - it just took them longer. A decline in fertility in the late 20s, what we found was a decrease in the probability of becoming pregnant per menstrual cycle, not in the probability of eventually achieving a pregnancy. Researchers found a wide range of rates of fertility between the couples studied, regardless of their age.

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How does it vary?

Just like every woman has a different age for reaching puberty, so too the exact age where a woman’s biological clock stops ticking – in other words menopause -  will be different for different women. In the United States, the average age of a woman having her last period, menopause, is 51³. But, some women have their last period in their forties, and some have it later in their fifties. However the age for women experiencing menopause can depend on many other factors like race, ethnicity, lifestyle and other health parameters.

Certain lifestyle factors like smoking can also lead to early menopause. While research has long been convinced that smoking in pregnant women could be related to higher risk of miscarriage, its effect on women’s seems more pervasive than before. A research⁴ conducted at Boston's Massachusetts General Hospital have found out that toxic chemicals in cigarette smoke can prematurely trigger the genetic signals that cause a woman's egg cells to die and her ovaries to shut down, thus in effect bring her biological clock to a stop.

Certain types of cancer therapy - chemotherapy and/or radiation therapy - can also result in menopause if given to an ovulating woman. Premature ovarian failure is defined as the occurrence of menopause before the age of forty. This condition occurs in about 1% of all women. The cause of premature ovarian failure is not fully understood, but it may be related to autoimmune diseases or genetic factors.
Other factors
Some though would argue that there are other than biological factors which contribute to a woman’s concern over the ticking of her fertility clock. According to Gary and Sandra Brase, researchers from Kansas State⁵ “Baby fever is this idea out in popular media that at some point in their lives, people get this sudden change in their desire to have children…While it is often portrayed in women, we noticed it in men, too”. One of the primary factors which appears to contribute to whether baby mania would take hold of a woman or even man was positive exposure to a baby. In other words, if a woman spent a fair amount of time around the cutest and prettiest baby, she would be quite likely to want one of her own. But this implies that The opposite is true as well -- if she is exposed to negative aspects of raising a baby like dirty diapers, colicky wailing and sleep deprivation, it can significantly decrease her desire for having a child. Then there are practical factors also came into play in how loud a woman can hear the ticking of the biological clock -- issues like finances, career and her social life can also diminish or heighten a woman’s desire for having a baby.

What about men

The ticking away of the biological clock is primarily thought of as a female experience. This is because while a woman's egg supply is set before birth, a man produces sperm throughout his life. He experiences a slight decline in fertility as he gets older, but his semen doesn't lose its concentration. This is why men can continue to father children even in old age and hence, the ticking of the biological clock is not an overriding concern with them.

However just because just because a man can make sperm doesn't mean it's high-quality sperm. As men age, the volume, motility (speed), and quality of their sperm decline which in turn means a decline in fertility, and a greater chance of fathering children with genetic problems. Besides with advancing age, men also experience declining levels of the male hormone testosterone which has an impact on their sexual capabilities.

In a study⁶ published in the journal Fertility and Sterility, researchers interviewed nearly 2,000 women to find out how long it took them to conceive. Among women 35 and older, those whose male partners were 45 and older took five times longer to conceive than those whose partners were 25 and younger. The researchers also looked at what happens when young women (age 25 and under) have children with men 45 and older. The researchers found a fourfold increase in the time it took couples to conceive – meaning the man's age was a factor independent of the woman's age.

Fertility is a highly complex phenomenon, whether in men or women. Scientists are still unearthing new facts about how hormones, genes and lifestyle factors influence a woman’s ability to conceive and bear children. But so much is certain that among all human biolocial systems, the female reproductive system is one of the most sensitive to the vagaries of aging.

References:

1. Bloomberg - Female Biological Clock Runs Out as Egg Repair Genes Wane
    
2. Mail Online - The female fertility clock 'starts ticking at 27'
    
3. National Institute on Aging – Menopause
    
4. Mail Online - Now smoking causes infertility and early menopause!
    
5. Mail Online - What sets off your biological clock? Teeny, tiny sneakers
    
6. Kidd SA, Eskenazi B, Wyrobek AJ. Effects of male age on semen quality and fertility: A Review of the literature. Fertility and Sterility. 2001;75(2):237-248.