Developmental abnormalities, including those leading to miscarriage and autism, are primarily controlled by the genetics of the fetus and placenta.
Abnormalities of the placental trophoblast bilayer – the primary barrier between maternal and fetal tissues – are known as trophoblast inclusions. These abnormalities are linked with aneuploidy and miscarriage. However, it has not been known whether they occur due to the mother's uterine environment or the genetics of the fetus.
'Mothers often feel that they are responsible for these defects. But it's not their fault,' said Dr Harvey Kliman, senior author and researcher at Yale School of Medicine, Connecticut. 'This new research points to the genetics of these children as being the most important cause.'
In a study published in Placenta, the scientists examined placental data from 48 sets of identical and non-identical twins. They discovered that trophoblast inclusions were present with similar frequency in identical twins, yet non-identical twins showed a significantly different number of trophoblast inclusions.
Identical twins share the same DNA sequence, whereas non-identical twins share an average of half of their DNA sequence – the same as non-twin siblings.
As a non-identical twin, lead author Julia Katz, a former Yale undergraduate who is now a medical student at Hofstra University, New York, included her own placental slides from birth in the study.
Katz's twin brother was born underweight and with several congenital abnormalities, 'I had a lot of guilt, growing up, about why my twin had certain conditions that I didn't,' Katz explained. 'I think mothers also tend to blame themselves.'
The authors concluded that developmental abnormalities are influenced by the genetic makeup of the fetus and that the resulting trophoblast inclusions can serve as a marker of genetic abnormality.
'This work suggests that developmental abnormalities are much more likely to be due to the genetics of the child, and not the mother's fault,' Dr Kliman concluded.
According to the Centres for Disease Control and Prevention, birth defects affect one in every 33 babies born in the USA each year and are the leading cause of infant deaths, accounting for 20 percent of all infant deaths.