The first gestational weeks are essential for the normal development of the brain. While this is an intricate process between genes and environment, certain environmental factors, such as endocrine disrupting chemicals (EDC) and their mixtures, and adverse life events (ALE), may disrupt this process. However, more knowledge is needed on how these environmental factors contribute to neurodevelopmental outcomes. It is also unknown if maternal thyroid hormones might mediate the associations and how children’s play behaviour is associated with neurodevelopmental outcomes.

The aim of the thesis is to explore the importance of prenatal exposure to EDCs and their mixtures and ALE for children’s neurodevelopmental outcomes, examine if maternal thyroid mediates such associations, explore neurodevelopmental outcomes in relation to play behaviour, and identify whether associations differ between boys and girls.

Data from the Swedish Environmental Longitudinal Mother and child Asthma and allergy study have been used in this thesis. Urine and serum samples have been collected from the mother during early pregnancy to measure the concentrations of EDCs and thyroid hormones. Data on ALEs were collected by questionnaire when the children were 4 years old, and behavioural outcomes and cognitive function as well as play behaviour were assessed when children were 7.5 years old using validated instruments.

Results show that prenatal exposure to EDC mixtures was associated with behavioural difficulties in children, with differences observed between boys and girls. Maternal thyroid function emerged as a potential biological mechanism underlying these associations. Furthermore, ALEs during pregnancy were linked to behavioural, but not cognitive outcomes. Lastly, children's play behaviour was associated with behavioural outcomes.

In conclusion, EDCs and ALEs are associated with neurodevelopmental outcomes, and there are co-occurrences between children’s play and neurodevelopmental outcomes.

As brain development begins early in pregnancy, exposure to environmental factors during this sensitive period can interfere with this process. This thesis explores two such factors—endocrine-disrupting chemicals (EDCs) and their mixtures and adverse life events—in relation to neurodevelopmental outcomes, along with the biological mechanisms that may explain these associations. We used data from the Swedish Environmental Longitudinal Mother and child Asthma and allergy (SELMA) study, which included pregnant women in Värmland and followed them until the children were 7.5 years old. The exposures of interest were urine and serum concentrations of EDCs and adverse life events during pregnancy within the family. The neurodevelopmental outcomes of interest were behavioural difficulties, autistic traits and cognitive function.

Prenatal exposure to EDC mixtures was associated with behavioural outcomes in children at 7.5 years, with differences observed between boys and girls. Maternal thyroid function emerged as a potential biological mechanism underlying these associations. Furthermore, adverse life events during pregnancy were linked to behavioural, but not cognitive outcomes, in the offspring. Lastly, children's play behaviour was associated with behavioural outcomes.