Sex, Stress, And Perinatal Development

Researchers at the University of Adelaide have found that the sex of a fetus can determine its response to stressors occurring during the period of gestation and may make or break the baby's ability to survive in spite of complications. It seems that male and female babies have different rates of growth and development when subjected to stressors during pregnancy. Such stressors would include cigarette smoking, psychological stress, or maternal disease.

Growth Patterns

The study is being conducted by the Pregnancy and Development Group at the Robinson Institute which is located at the Lyell McEwin Hospital and is headed up by Associate Professor Vicki Clifton. "What we have found is that male and female babies will respond to a stress during pregnancy by adjusting their growth patterns differently," said Clifton.

Clifton explains that the male fetus seems to go into denial when his mother is stressed. He ignores the stressors and keeps on growing. He wants to get as big as possible. But the female will slow her rate of growth just a bit. She doesn't slow things down so much that she ends up with intrauterine growth restriction (IUGR), but nonetheless her growth will fall just below average.

However, if another complication should arise from a different stress or if the same stress is repeated, the female fetus will still continue to grow at a rate just below the norm and do just fine, while the male baby can't seem to cope. He ends up at a greater risk for pre-term delivery, aborted growth, or death in utero.

Cigarette Use

Clifton says that these growth responses that are specific to the sex of the fetuses have been seen in pregnancies that have been complicated by cigarette use, pre-eclampsia, and asthma. She says that the same growth responses would be seen during other stressful occurrences in gestation, for instance in response to a mother's psychological distress. Clifton attributes the sex-specific growth patterns to changes in the way the placenta functions in the presence of cortisol, the human stress hormone.

It seems that increased cortisol levels change placental function so that a female's growth is slowed, but that a male baby doesn't affect the same changes in the way the placenta works.

Professor Clifton's hope is that this study might lead to new and better therapies for pre-term pregnancies and for premature newborns, tailor-made to the sex of the fetus. The findings should also help obstetricians to better interpret the status of fetal growth and development in the case of high-risk pregnancies. "We are looking at what events during pregnancy cause changes in how the baby grows, what's behind this and ways in which we can improve the outcomes for pregnant women and their babies," said Clifton.