Infertility rates worldwide have remained relatively unchanged over the last 20 years, a new global study has found.
The study, conducted by international researchers and led by the World Health Organisation (WHO), involved examining data from 277 national surveys in 190 countries covering the years 1990 to 2010. The results were published today in the journal PLOS Medicine.
The researchers defined infertility as an inability to conceive after five years of trying and delivering a live baby.
The study found that in 2010, 48.5 million couples were unable to have a baby after trying for five years. The researchers also found that in 2010, 1.9% of women aged between 20 and 44 were unable to have a first child and 10.5% of women who already had one child were unable to have a second.
“These findings also suggest that global levels of primary and secondary infertility hardly changed between 1990 and 2010,” the researchers wrote but added that different definitions of infertility may yield a different result.
“It is important to note that an infertility measure based on ability to become pregnant (rather than having a live birth — the outcome used in this study) may show different levels of infertility, and using an exposure period shorter than the five years used in this study would produce higher rates of infertility,” the study said.
Lead researcher Dr Gretchen Stevens from the Department of Health Statistics and Information Systems, World Health Organisation said the paper used a demographic definition of infertility.
“We can calculate infertility prevalence using hundreds of demographic surveys with our definition, whereas only a handful of population-based surveys measure infertility using a typical clinical definition,” she said.
While BMI and diabetes rates had increased in many high-income countries, so had the mean age at childbirth and age was an important risk factors for infertility, she said.
“Nevertheless, we have found no change in primary infertility (first live birth) and only a modest increase in secondary infertility (additional live birth) from 1990 to 2010 in high-income countries. This is supported by the results from the U.S. National Survey of Family Growth during the same time period, which used a definition more similar to the one that most clinicians use,” said Dr Stevens.
“Overall, infertility has many causes that may interact in ways that are difficult to predict. That’s why we attempted to directly measure levels and changes in infertility prevalence. An interesting parallel are cardiovascular death rates, which have declined dramatically in the face of the increases in BMI and diabetes.”
Dr Jeremy Thompson, Associate Professor in Paediatrics and Reproductive Health at the University of Adelaide, said he was surprised by the result.
“In Western countries where the levels of obesity and type 2 diabetes has increased dramatically over the last few decades, there is infertility associated with those problems,” said Dr Thompson, who was not involved in the study.
“And a lot of emerging economies have got the same kind of disease problems of a more high fat, high protein diets. All these metabolic diseases do have an effect on fertility.”
Obesity could cause infertility in men as well as women, he said.
“So I am surprised at this study. It depends on what our definition of infertility is and I would say five years [of trying], that’s a pretty stringent definition [of infertility] – in Australia we would say trying for one year.”