Ideally, the sex ratio at birth should be 1 boy to 1 girl. However, the practice of sex selection might determine the ratio in any given country. For instance, about 105 boys are born for every 100 girls in Iran. The current global sex ratio is 107 boys to 100 girls.
It seems that the ratio is going to change and the number of women in population is likely to rise in coming years with increasing number of heart disease cases.
Researchers from Tabriz University in Iran reported on April 20, 2012 at the World Congress of Cardiology in Dubai that pregnant women with heart disease were more likely to give birth to girls.
Their study involved 200 pregnant women who had heart disease and were referred to a heart center for delivery. They gave birth to a total of 216 babies, of which 75 percent were girls, or 32 boys were born for every 100 girls. The average age of the women was 29.
Among these women, 64 percent had a form of heart disease that involves problems with the heart valve, 19 percent had dilated cardiomyopathy (a condition in which the heart becomes weakened and enlarged and is not able to pump blood efficiently), and 14 percent had a problem with their heart's structure and function that was present since birth.
It has been known that the chromosomes in a man’s sperm determine the sex of a baby. Sperm carry either an X or Y chromosome, while eggs carry only an X chromosome. A sperm cell with an X chromosome unites with an egg will give birth to a girl. On the other hand, a sperm with a Y chromosome unites with an egg will give birth to a boy.
The researchers admitted that the reason for the skewed sex ratio among babies born to women with heart disease is not known. But the study did suggest the health status of the mother might be related to the sex of the babies she is able to carry to full-term.
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