Older fathers were also linked with autism with every additional five years increasing the risk by 3.6 per cent
Children of older parents at increased risk of autism
Children born to older parents or whose mother suffered complications during pregnancy are at increased risk of developing autism, a review of research has found.
By Rebecca Smith, Medical Editor Published: 7:00AM BST 01 Jul 2009
Harvard researchers examined 64 studies which looked at various factors such as order or birth, parents' age, and complications such as bleeding during pregnancy and the subsequent risk of the child developing autism.
The strongest links were found with mothers over the age of 30, bleeding during pregnancy, developing diabetes while pregnant, using medication while pregnant and being first born.
The research discovered that developing diabetes during pregnancy increase the risk of autism two-fold, bleeding during pregnancy increased the risk by 81 per cent and maternal medication use by 46 per cent.
Becoming a mother over the age of 30 increased the risk of autism by between 27 per cent to 106 per cent according to different studies included in the review. Older fathers were also linked with autism with every additional five years increasing the risk by 3.6 per cent.
Age is probably linked with autism because of greater damage to eggs and sperm as parents age, which in turn affects the quality of the embryo and developing foetus.
The analysis also found that being first-born increased the risk of autism by 61 per cent compared with children born third or later.
However the research, published in the British Journal of Psychiatry, said there was no one factor which could be singled out as most important. They said complications in pregnancy in general appeared to increase the risk of having a child with autism.
The researchers also suggested that the reason for this may be that there is a common cause for both the complications and the autism, rather than the complications themselves being responsible for the condition.
The researchers said there was "insufficient evidence" to point to any one prenatal factor as being particularly significant. However, they said: "There is some evidence to suggest that exposure to pregnancy complications in general may increase the risk of autism."
The review found there was strong evidence that several factors did not increase the risk of autism including previous miscarriage, high blood pressure and pre-eclampsia and swelling.
There are thought to be 588,000 people in Britain with autism spectrum disorder, including Asperger syndrome, which is a developmental disability that affects the way a person communicates and relates to people around them. People with autism have difficulties with everyday social interaction.
Fear of the condition was behind a dramatic fall in the number of children being given the triple jab for measles, mumps and rubella, following discredited research which linked it to bowel disease and autism.
A spokesman for The National Autistic Society said: "The causes of autism are not yet understood but there is evidence to suggest that autism can be caused by a variety of genetic, physical and environmental factors which affect brain development, although as yet we don't fully understand how or why this happens.
"Research into the causes of autism can cause concern and worry amongst parents of children with autism, and potential anxiety for expectant mothers or new parents. Particularly, as there is much confusion over the various theories put forward.
"Whilst research continues, it is crucial that parents have access to appropriate advice and support, as well as the services to enable them to cope with living with autism in their daily lives."