The causes of autism spectrum disorder (ASD) are complex and remain unclear. A recent study, involving more than 3.5 million children, now shows that the risk of ASD may slightly increase for each week a baby is born before or after 40 weeks of gestation.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, affecting 1% to 2% of children worldwide. Children with this disease cannot initialize or take part in social communication and have repetitive behaviours. The reasons may be genetic and related to environmental factors, and there are still a lot of unsolved puzzles in this field.

© Unsplash / Andrew Seaman

A group of scientists analysed data of 3.5 million children born in Sweden, Finland or Norway between 1995 and 2015. The goal of the study was to explore a potential correlation between gestational age (at which week a child is born) and the risk of Autism Spectrum Disorder. The results show that the children born at term (in weeks 37-42) had the lowest risk rate of 0.83. This risk rate represents the percentage of babies with ASD in the specific group: a risk rate of 0.83 means that less than one baby born at term had ASD in the study population. For the babies born preterm in weeks 22-31, the risk rate for ASD was about 1.67, while for the babies born preterm in weeks 32-36 the risk rate was 1.08. Finally, post-term birth, in weeks 43-44, was associated with the highest risk rate observed (1.74).

The results suggest that preterm and post-term birth can be related to ASD. However, the main limitation of the study is the lack of information on the potential causes for either pre- or post-term birth. More research is required to clarify the link between pre- and post-term birth and ASD.

The study is based on nationwide data from Sweden, Finland, and Norway, made available from the European Union’s Horizon 2020 research and innovation program “RECAP preterm” (Research on European Children and Adults born preterm, www.recap-preterm.eu). Please see the following link for more information regarding the RECAP preterm project and EFCNI’s involvement: www.efcni.org/activities/projects-2/recap

Paper available to view at: PLOS Medicine

Full list of authors: Martina Persson, Signe Opdahl, Kari Risnes, Raz Gross, Eero Kajantie, Abraham Reichenberg, Mika Gissler, Sven Sandin

DOI: 10.1371/journal.pmed.1003207