Babies whose mothers were stressed when they were pregnant could end up with worse cognitive development than their peers. But any effects on cognitive development can be almost completely overcome by good parenting. A study led by Professor Thomas O'Connor from the University of Rochester Medical Centre measured the levels of the stress hormone cortisol in 125 women as they underwent amniocentesis. When the children were 17 months old the researchers assessed the baby's cognitive development using puzzles, pretend play and memory tests. They also gauged the quality of the relationship between the mothers and their babies using a test in which children are briefly left alone and then reunited with their mothers. The study found that for children with an 'insecure' attachment to their mothers a high prenatal cortisol level was linked to shorter attention spans and weaker language and problem-solving skills. However, there was no link between prenatal cortisol levels and cognitive development in children who had a secure relationship with their mother.
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