Global rates of infertility have remained relatively stable between 1990 and 2010, according to a study that compiled data from 277 national surveys in 190 countries.
Research by the World Health Organisation (WHO) estimated that in 2010, 48.5 million couples worldwide were unable to have a child. They found that 1.9 percent of women aged 20-44 who wanted a child were unable to have their first live birth and 10.5 percent of women who had previously given birth were unable to have another baby after five years of trying. This represented a 0.1 percent and 0.4 percent decrease from 1990, respectively.
'Independent from population growth and worldwide declines in the preferred number of children, we found little evidence of changes in infertility over two decades', the authors wrote, adding that 'further research is needed to identify the etiological causes of these patterns and trends'.
A notable exception to the overall trend was seen in sub-Saharan Africa, where infertility rates fell markedly. The lead author, Dr Gretchen Stevens from the Department of Health Statistics and Information Systems at the WHO, suggested that a reduction in sexually transmitted infections – which can cause infertility if left untreated – as well as improved obstetric care might have contributed to this fall.
'One of our hypotheses is that perhaps some of the changes in behaviour that have come about in response to the HIV (human immunodeficiency virus) epidemic might actually have gone towards reducing infertility rates', she said.
The researchers defined infertility as failing to achieve a live birth after five years of trying to conceive. This differs from typical clinical definitions based on failure to achieve a clinical pregnancy after 12 or more months of trying.
The authors justified their choice as it allowed infertility prevalence to be calculated from hundreds of surveys that collected data on births, couple status, fertility preferences and contraceptive use. Few surveys asked about how long a woman had been trying to get pregnant or collected reliable data on miscarriages, terminations or medical history.
Dr Jeremy Thompson, associate professor in paediatrics and reproductive health at the University of Adelaide, who was not involved in the study, expressed surprise that infertility rates had remained stable despite a dramatic rise in levels of obesity and type 2 diabetes over the last few decades.
'All these metabolic diseases do have an effect on fertility', he said. Nonetheless the study found no evidence to support concerns that higher numbers of older women wanting children and environmental factors affecting sperm quality may have contributed to declining fertility in higher income countries.
The results were published in the open access journal PLOS Medicine.