Danish doctors who studied 2.4 million kids say they have higher risk of conditions such as autism if mum had trouble conceiving

Children born to women with fertility problems are more likely to develop psychiatric disorders than those with healthier mothers, research suggests.

Doctors found higher rates of mental problems – from anxiety and schizophrenia to autism – in children whose mothers had issues getting pregnant.

The scientists could not explain the findings but said genetic faults or other biological problems with the mother were more likely to blame than any fertility treatment they had.

"The exact mechanisms behind the observed increase in risk are still unknown but it is generally believed that underlying infertility has a more important role in adverse effects in offspring than the treatment procedures," said Allan Jensen, an epidemiologist at the University of Copenhagen in Denmark.

One possibility is that faulty genes that raise the risk of psychiatric diseases are more common in women with fertility problems. "If transferred to their offspring, this may at least partly explain the increased risk of psychiatric diseases," Jensen said.

The Danish group used a database that links patient records, allowing them to study the medical histories of parents and their children. They first searched for all children born in Denmark between 1969 and 2006. From a total of more than 2.4 million, they separated out 124,000 (5%) born to women with registered fertility problems, and 2.3 million (95%) whose mothers had no such problems.

The researchers followed the children's medical histories, typically for 20 years, until 2009. During that time, children born to women with fertility problems had a 33% higher risk of psychiatric disorders. The children had a 27% higher risk of schizophrenia and psychoses, a 37% higher risk of anxiety and neurotic disorders, an 28% greater risk of learning difficulties, and a 22% higher risk of mental development disorders, including autism spectrum disorders, the scientists found.

Further analyses of children aged 19 and under, and 20 and over found that the risks continued into adulthood.

Based on the figures, Jensen calculated that in Denmark, around 1.9% of all diagnosed psychiatric disorders are associated with the mother's infertility. "This figure supports our interpretation of the results, that the increased risk is real but modest," said Jensen, who will describe the work at the European Society of Human Reproduction and Embryology meeting in Munich on Monday. The research has not been published in a peer-reviewed journal.

Yacoub Khalaf, medical director of the assisted conception unit at Guy's Hospital in London, was sceptical of the figures. "As a clinical observation, if they suggest the risk of mental retardation is increased by 28%, surely over the years we would have seen an epidemic of mental retardation as a result of fertility treatment, which has never been observed. The figures are staggering and at odds with anything that's been reported so far."

Allan Pacey, chair of the British Fertility Society, said the results were intriguing. "I suspect we are seeing an effect of biology going on to affect these children or perhaps it's the social environment in which those young children were brought up."

Previous research on children born after fertility treatment suggests that certain procedures, such as intracytoplasmic sperm injection (ICSI), may raise the risk of birth defects, though the link is not definite.

But common fertility treatments do not seem to raise the risk of mental disorders. A major study published in the British Medical Journal last year by another Danish team found that children born after IVF and ICSI were no more likely to have mental disorders than children conceived naturally. The researchers did see a small increase of mental problems in children born after their mothers had ovarian stimulation followed by intrauterine sperm injection.

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