New study links high levels of oestrogen in the womb to autism

For the first time, new European research has found a link between high levels of oestrogen sex hormones in the womb and an increased risk of developing autism.

Carried out by researchers at the University of Cambridge, UK, and the State Serum Institute and Hospital of Southern Jutland in Denmark, the new study looked at samples of amniotic fluid taken from 275 individuals participating in the Danish Historic Birth Cohort, which has collected amniotic samples from over 100,000 pregnancies.

The researchers tested the levels of four prenatal sex steroid hormones called oestrogens in the amniotic fluid samples. None of the samples differed significantly in maternal age at birth, paternal age at birth, birth weight, gestational week at the time the sample was taken or how long the samples had been stored for.

The findings, published on Monday in the journal Molecular Psychiatry, showed that all four oestrogens were significantly higher, on average, in the 98 male foetuses who later developed autism, compared to the 177 male foetuses included in the study who did not.

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Levels of estradiol levels were the most predictive of an autism diagnosis, which the team had expected, as it is the most potent oestrogen.

The results build on a 2015 study carried out by the team, which also used samples from the Danish Historic Birth Cohort. The findings from this study showed that levels of four prenatal steroid hormones, including two known as androgens, in the amniotic fluid in the womb were higher in male foetuses who later developed autism.

As these androgens are produced in higher quantities on average in male than in female foetuses, the 2015 findings might also explain why autism occurs more often in boys.

Moreover, the new research showed that high levels of oestrogens in the womb appear to be even more predictive of the likelihood of autism than high levels of prenatal androgens such as testosterone. Although oestrogen is often associated with feminization, prenatal oestrogens actually also masculinise the brain in many mammals.

Lead author Professor Simon Baron-Cohen commented, "This new finding supports the idea that increased prenatal sex steroid hormones are one of the potential causes for the condition. Genetics is well established as another, and these hormones likely interact with genetic factors to affect the developing fetal brain."

Alex Tsompanidis, who also worked on the study, added, "These elevated hormones could be coming from the mother, the baby or the placenta. Our next step should be to study all these possible sources and how they interact during pregnancy."

The team stressed that these findings cannot and should not be used to screen for autism. "We are interested in understanding autism, not preventing it," added Baron- Cohen.