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The odds of baby boy or girl depends on how much sex you have

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Always wanted to know the secret on how to have a baby girl or a boy? Here’s a study that throws light on the process of baby-making. According to Daily Mail, the study which is the most in-depth of its kind uses statistics of fertility advice over 300 years old – before contraception. The assumption is based on figures that are 300-years-old.This also includes information from French parishes collected by French historian Louis Henry, who died in 1991. In between the 18th and 19th centuries — crucially, pre-contraception was used to calculate ‘natural’ fertility rates.

The study shows how the fertility rate of a 35 to 39-year-old woman not using contraception is commonly assumed to be 34 per cent, compared with 48 per cent for those aged 20 to 24. From 40 to 44, it drops to 17 per cent and is less than 5 per cent by 45.But in the 1700s many older women would have been breastfeeding from a previous birth, which would have limited their ability to get pregnant. Additionally, those over 35 may well have already given birth to six or seven children, suffering complications that left them sterile. And, crucially, if women didn’t want more children they were probably avoiding sex altogether. Clearly, they have little in common with modern women who have delayed starting a family by choice.

Condoms and contraceptions also effectively stop pregnancies. While many admitted having problems from prophylactics that were put on the wrong way round to those that slipped off during love-making — in 2,248 monthly cycles where condoms were used for all sex there were just four pregnancies. From this, statisticians were able to arrive at the figure of 2 per cent. In 200, a US study estimated a ‘typical’ failure rate of 18 per cent after a survey of 7,643 women — who said they relied on condomsrevealed that 14 per cent had got pregnant after a year, presumably due to incorrect use.

The study concludes that evolution has enabled women to have more boys in times of great loss of men as they will do better in a society short of males. The most coherent explanation is that the sex of the foetus is influenced by the hormone levels of the parents at conception, with more boys being conceived earlier on in the cycle. The peak fertile time for a woman is around two days before ovulation but if couples have a lot of sex they are more likely to conceive before the woman reaches this peak, at an earlier point in her cycle.

Obviously during, and just after, major wars sex has to be crammed into brief periods of leave. So a couple will maximise opportunities for making love with intense bouts of activity, with less consideration to where a woman is in her cycle. So more conceptions are likely to occur earlier in the fertile period and therefore give a higher chance of having a boy. This theory is backed up by another peak for boys in the UK in 1973. While there was no war on, this is when the average age of women at marriage was at its lowest — 21 — and there was a surge of teenage pregnancies and it was a time of intense sexual activity in the young.

While more boys are born at the end of wars, relatively more girls are born in times of prolonged parental stress for example, as happened after the 1995 Japanese earthquake and in New York in the wake of the destruction of the Twin Towers in 2001. Prolonged financial hardship also produces a similar trend. Researchers investigating miscarriages in California found that there were more miscarriages of male babies when the unemployment rates were higher between 1989 and 2001. So the most likely explanation for this pattern is that stress during pregnancy leads to more miscarriages of male than female foetuses.

Another way to look at this would be stress is a well-known passion killer. Also if more sex produces more boys and less sex produces more girls, then looking at the proportions of boys to girls at any time may give us an idea of how much sex was being had.

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