It is not always possible to determine the exact cause, but it is now clear that many cases of female infertility today are simply age-related and explained by nothing more than a reduction in the number and quality of eggs available in the ovaries. It's for this reason - what is known as 'ovarian reserve' - that fertility rates begin to decline after the age of 35 (in both spontaneous and assisted conception).
Today, as more and more women defer their first pregnancy until careers and finances are more settled, we are seeing ever more cases of infertility whose cause is related to the availability of fewer good quality eggs and embryos. And this too is one of the big challenges of fertility treatment today.
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