A study has shown that women who took folic acid supplements in early pregnancy almost halved the risk of having a child with autism.
Beginning to take folic acid supplements later in pregnancy did not reduce the risk.
The study findings from the ABC Study and Norwegian Mother and Child Cohort Study published in the Journal of The American Medical Association was made available to the Ghana News Agency on Thursday.
It said women who took folic acid supplements from four weeks before conception to eight weeks into pregnancy had a 40 per cent lower risk of giving birth to children with childhood autism (classic autism).
It said the use of folic acid supplements midway through pregnancy (week 22) had no effect.
The findings only apply to a lower risk of childhood autism, the most severe form of autism.
The results show no reduction in the risk of atypical or unspecific autism.
The study also investigated the prevalence of Asperger syndrome, but the number of examined children was too low to give a reliable result.
The researchers found no connection between childhood autism and intake of other supplements during pregnancy.
They also found no correlation with maternal intake of folate through food.
The results show an association between the use of folic acid supplements in the mother during pregnancy and a reduced risk of childhood autism.
The results supported the Norwegian Directorate of Health's recommendations for folic acid supplements during pregnancy and emphasised the importance of starting early - preferably before conception.
The ABC Study included participants in the Norwegian Mother and Child Cohort Study (MoBa) who were born in 2002-2008, and included a total of 85,176 children.
It said the mothers had given detailed information about their diet and the use of supplements in early pregnancy.
The study said children with autism diagnoses in MoBa were identified through questionnaires, referrals from parents and health personnel and through links to the Norwegian Patient Register.
It said when the analyses were done, 270 children with autism diagnoses were identified in the study population; of these children, 114 children had autism, 56 had Asperger syndrome and 100 had atypical or unspecified autism.
It said the use of folic acid supplements in early pregnancy increased sharply from 2002 to 2008 among women who participated in the Norwegian Mother and Child Cohort Study.
It said 43 per cent of mothers took folic acid supplements in 2002, while the percentage had risen to 85 per cent in 2008; however, many women began later than is desirable; only half of women who took folic acid supplements had begun before conception.
The Norwegian Directorate of Health recommends that women who were planning to become pregnant should take folic acid supplements from one month before conception and during the first three months of pregnancy.
The recommendation was based on research showing that the use of folic acid supplements in early pregnancy protected the foetus from spina bifida and other neural tube defects.
The ABC Study was a large research project conducted by the Norwegian Institute of Public Health in collaboration with Columbia University in New York, USA.
The goal was to investigate causes of autism and to study how autism spectrum disorders develop in children.
The study was nested within the Norwegian Mother and Child Study.