Variants in the foetus's DNA - not the mother's - may be what triggers some preterm births, scientists have found.
Joseph R Biggio, of the University of Alabama, and his colleagues from the Eunice Kennedy Shriver Genomics and Proteomics Network for Preterm Birth Research analysed the number of copies of certain genes in the blood or saliva from hundreds of babies and their mothers.
While there was no link between the number of copies of the mother's genes and the chances of a preterm baby, there was a two- to eleven-fold increase in preterm births before 34 weeks of pregnancy when any of four genes were duplicated or seven genes were deleted in the babies born preterm, when compared to babies born full-term.
"These findings may help explain what triggers early labour in some women even when they've done everything right during pregnancy and there's no obvious cause for an early birth," said Edward McCabe, Chief Medical Officer at March of Dimes, a US nonprofit.
"The hope is that this finding may one day lead to a screening test to help identify which babies are at a higher risk of an early birth," McCabe said.
Preterm birth (birth before 37 weeks of pregnancy) is the leading cause of newborn death, and babies who survive an early birth often face an increased risk of a lifetime of health challenges, such as breathing problems, cerebral palsy, intellectual disabilities and others.
Even babies born just a few weeks early have higher rates of hospitalisation and illness than full-term infants.
While the differences in the number of copies of the genes may not be causing a preterm birth, they may put a baby at a higher risk of infection or reacting to other harmful environmental factors that may trigger early labour and delivery, said Biggio.
It may also help explain why treatment with progesterone, a naturally-occurring hormone in pregnancy shown to prevent some preterm births, works for only about one-third of women.
The study will be presented at the Society for Maternal-Fetal Medicine's annual meeting in San Diego this week.
