What are you hoping for - a boy or a girl? 'As long as it's healthy' is the common reply, but couples have been trying to influence the gender of their babies for thousands of years and it's still going on today
Last month's issue of the Lancet featured research claiming that couples who smoke around the time of conception are more likely to have a daughter. Researchers at the University of Copenhagan interviewed the mothers of 11,800 babies born in Denmark and Japan over a seven-month period. The babies' mothers were questioned about their own and their partners' daily smoking habits around the time of conception. The more cigarettes smoked by both partners, the more likely they were to have a daughter, according to the study.
What does this mean? Hopefully not a return to smoking by parents dying for a girl. The researchers in this particular study posited the theory that the male sperm cell may be more susceptible to smoking. The news that unhealthy parents may create more girls is not, however, news.
Writing in The Red Queen: Sex and The Evolution of Human Nature in 1993, science writer Matt Ridley described some of the factors that have been proven to influence gender at conception. "Older fathers are more likely to have girls, older mothers are more likely to have boys. Women with hepatitis or schizophrenia have more daughters. So do women who smoke or drink . . . women with multiple sclerosis have more sons as do women who consume small amounts of arsenic."
Theories abound. The most famous, according to Ridley, is the "returning-soldier" effect. During and immediately after major wars, more sons than usual are born in the warring countries. This statistical oddity has been linked to another theory that suggests that dominant women give birth to more sons. In war situations, women are left at home to take control of domestic affairs. Does this affect their hormone levels and thus their tendency to create boys? Fortunately for families in Ireland, there is no social pressure preferring either sons or daughters. However, after the first child is born many parents will start to hope for some gender diversity in the family. Most expectant parents will experience a mild yearning for a baby of one gender or another.
For some couples, it's a great deal more than a mild yearning. So desperate are some for a child of a specific gender that an industry of gender determination techniques has sprung up in the US. It's not a new phenomenon - people have been trying to influence the gender of their offspring for centuries. In 1200 BC, the book of Leviticus in the Bible mentions that couples who allow the woman to orgasm before the man will bear sons. Anaxagoras, a 5th-century BC Greek philosopher believed that semen from the right testicle produced sons, while semen from the left testicle resulted in the birth of a daughter. His theory stubbornly prevailed for centuries - some French aristocrats had their left testicles removed in order to bear sons.
A number of gender selection techniques based on scientific theories have been developed in recent years, but not one has been endorsed by the entire medical community. Modern day sex selection techniques are arguably as hit and miss as their old time equivalents. Nevertheless, many couples are prepared to spend large sums of money, and considerable time, perfecting procedures that supposedly influence gender.
The most commonly used sex selection technique requires couples to time intercourse carefully in the days leading up to ovulation. Sex is determined by the sperm, and sperm carrying the female chromosome are slightly heavier than sperm carrying the male chromosome. There is a theory that the heavier female sperm is hardy but slow while the male sperm is quick but fragile. Therefore, it has been suggested that if a couple has sex several days before ovulation, the female sperm is more likely to survive until ovulation day, when the egg arrives. If the couple has sex on ovulation day, however, the quick male sperm is likely to beat the slow female sperm to the prize.
Many couples have tried this method but it is by no means proven. A 1995 study published in the New England Journal of Medicine explored the connection between ovulation, intercourse and gender. "We found no relationship between the timing of intercourse and the sex of the baby," Dr Clarice Weinberg of the National Institute of Environmental Health Sciences said.
Researchers at the Genetics & IVF Institute in Fairfax, Virginia, say they can help parents choose the sex of their baby through a procedure in which DNA is stained with a fluorescent dye. Because Y-chromosome sperm (which produce boys) has 2.8 per cent less genetic material than X-chromosome sperm (which produce girls), researchers say they can spot the larger sperm once the fluorescent dye has been added. This can then be artificially inseminated into the woman. However, not many parents are keen to give their progeny a neon douche.
Another technique, patented by Dr Ronald Ericsson and used in many fertility clinics in the US, attempts to separate the girl and boy chromosomes by filtering the sperm through a water-soluble protein solution called albumin. This method has not been endorsed by the medical community at large so the search for a fail-safe gender selection technique continues.
For now let's be glad that no technique has been found. Author and scientist Matt Ridley reminds us why sex selection is perhaps best left to nature.
"In some societies the preference for boys seems to have spread from the elites to the society at large. China and India are the best examples of this. In China a one-child policy may have led to the deaths of 17 per cent of girls. In one Indian hospital, 96 per cent of women told they were carrying daughters aborted them while nearly 100 per cent of women carrying sons carried them to term. This implies that a cheap technology allowing people to choose the gender of their children would indeed unbalance the population sex ratio."
