Infertility is on the rise in Canada, according to the first study in nearly two decades to measure the proportion of Canadian couples who are having difficulty conceiving.

The researchers didn't set out to discover why the numbers are increasing. But possible explanations range from the growing number of women pushing back pregnancy later in life to rising rates of obesity and heavy drinking among women and declining sperm counts in men - though experts aren't convinced about that final factor.

The use of assistedprocreation technologies has increased dramatically over the past decade, yet "little is known about the prevalence of infertility in the population," the authors write in the journal Human Reproduction.

The research was supported by funding from Assisted Human Reproduction Canada, a federal agency. The lead author is from Statistics Canada.

According to their estimates, up to 16 per cent of heterosexual couples where the woman is age 18 to 44 are experiencing infertility - a near doubling since 1992, when infertility was previously measured in the nation.

Not surprisingly, the older the woman, the higher the prevalence of infertility. Yet infertility appears to be rising among younger women as well, the study finds.

In 1984, about five per cent of couples with a female partner age 18 to 29 were infertile.

By 2009-10, the prevalence for the same age group ranged from seven to 13.7 per cent.

For their analysis, researchers used data from a sample of 4,412 couples from the 2009-2010 Canadian Community Health Survey.

Infertility ranged from 11.5 per cent to 15.7 per cent.

Those estimates are based on whether couples had reported becoming pregnant in the past 12 months, were not using any form of birth control within the past 12 months while having sexual intercourse and had tried to become pregnant with their current partner.

Regardless of how it was defined, each estimate represented an increase in infertility when compared with previous national estimates, said first author Tracey Bushnik, a senior analyst at Statistics Canada.

In 1992, 8.5 per cent of women age 18 to 44 who were married or living common-law were considered infertile.

In 1984, the figure was 5.4 per cent.