Severe stress during pregnancy can damage a baby's brain and put the child at greater risk of anxiety, depression and Attention Deficit Hyperactivity Disorder later on in adolescence, according to British research revealed last week.
The higher the levels of cortisol - a stress hormone - in the womb, the lower the toddler's "baby IQ" at 18 months, the researchers found.
"We found that if the mother was more stressed while she was pregnant the baby scored significantly lower on the mental developmental index," said Vivette Glover, lead researcher and professor of prenatal psychobiology at Imperial College London.
The study involved 250 women at 17 weeks gestation. They filled out questionnaires about their anxiety levels and the researchers monitored their cortisol levels and the amount seeping into their amniotic fluid.
Cortisol is naturally elevated during pregnancy, and rises again before a mother gives birth. Normally, the placenta protects the unborn baby from cortisol by producing an enzyme that breaks it down but the enzyme works less efficiently when the mother is stressed out.
The more anxious a mother was, the more cortisol appeared in her amniotic fluid, the researchers found.
Next, they will examine the children's brains using MRI scans; the oldest child is now six years old.
Experiments on pregnant primates have shown that stress can shrink a fetus's hippocampus by 30 per cent. The hippocampus plays an important role in memory, learning and emotional development. Maternal anxiety also affects other areas of the fetal brain, including the corpus callosum, which connects the right and left hemispheres, and the amygdala, which regulates our response to fear.
Canadian research is corroborating the British findings.
"If there's anything that we all agree on, it's that the fetus is incredibly vulnerable and fragile, and that even subtle perturbations in the mother's mood or her objective circumstances can have measurable effects on the fetus that last for years," said Suzanne King, an associate professor of psychiatry at McGill University.
Prof. King looks at stress, natural disasters and pregnant women. She studied 140 children born after the Quebec ice storm of 1998. Toddlers whose mothers felt severely anxious about that winter's hardships scored 15 IQ points lower than other local children, whose mothers experienced less stress and adversity in that period.
"That difference has been fairly well maintained through 81/2 years," said Prof. King.
She is now looking at the children's brain structures, and also separately studying 310 Iowa women who fell victim to the 2008 flooding.
"The end goal of our research is to be able to tell public-safety officials which women and their fetuses are especially vulnerable," Prof. King said.
The British researchers are also pushing for more professional support.
"In the developed world, the physical care of pregnant women is pretty good, but the emotional care is very, very lacking," Prof. Glover said.
"We need to be finding out about the emotional state of women in pregnancy, whether they're anxious, depressed or having problems with relationships with a partner, and then providing appropriate help."
The researchers also called out fathers: Prof. Glover said that 25 per cent of 125 respondents complained about emotional abuse from their partners.
"If women, while pregnant, said that their partner was emotionally cruel to them … that provided the kind of stress that related to lower baby IQ and to more anxiety in the child," Prof. Glover said.
She added that fathers sometimes feel excluded during pregnancy, and exhorted the protective role instead: "Fathers can help the development of their child right from when they're in the womb."
The researchers mounted their findings at the Royal Society Summer Science Exhibition last week.
Visitors played a game that showed how a mother's stress can increase the heart rate of her unborn baby. They also got to touch a real placenta, encased safely in plastic.