An unborn baby's whole genetic code has been mapped in the womb using DNA taken from its parents.
The technique could in future make it possible swiftly to scan for some 3500 genetic disorders before birth, without physically disturbing either foetus or mother.
Most pre-natal genetic screening currently involves tapping fluid from the foetal sac, or taking placental samples. This is done by either inserting a probe through the mother's abdomen or the neck of her womb.
Such invasive methods can only identify a small number of birth defects including Down's syndrome, spina bifida, cystic fibrosis and muscular dystrophy. They also pose risks for both mother and child.
But there are thousands of rarer genetic conditions that are seldom spotted until they start producing symptoms.
The new research involved analysing DNA shed by the foetus and floating in the mother's bloodstream.
Blood sample DNA from the mother was also studied as well as DNA extracted from the father's saliva.
Fitting pieces of the genetic jigsaw together, scientists in the US were able to reconstruct the entire genetic code of an unborn baby boy.
The findings were checked by looking at the baby's DNA after birth.
Parts of the baby's genetic material inherited from each parent were predicted with more than 98% accuracy.
Researchers were also able to identify 39 of 44 "de novo", or new, genetic mutations before the baby was born.
De novo mutations, which are not inherited, are responsible for a large percentage of genetic disorders.
They are thought to play a role in a number of complex conditions such as autism and schizophrenia.
The research is reported in the journal Science Translational Medicine.
Lead scientist Dr Jay Shendure, from the University of Washington in Seattle, said: "This work opens up the possibility that we will be able to scan the whole genome (genetic code) of the foetus for more than 3000 single-gene disorders through a single, non-invasive test."
In future, a more refined and less costly version of the procedure could make pre-natal genetic testing far more comprehensive than it is now, the scientists believe.
But they acknowledge that the ability to sequence a baby's whole genome in the womb has as yet unresolved ethical implications.
It could produce a wealth of data relating to a baby's future health.
At the same time, difficult questions may be raised about the moral case for terminating a pregnancy.
Interpreting the results, and communicating them to parents, also presented a big hurdle.
"The less tangible implication of incorporating this level of information into pre-natal decision-making raises many ethical questions that must be considered carefully within the scientific community and on a societal level," the researchers wrote.
"A final point is that as in other areas of clinical genetics, our capacity to generate data is outstripping our ability to interpret it in ways that are useful to physicians and patients.
"That is, although the non-invasive prediction of a foetal genome may be technically feasible, its interpretation - even for known Mendelian (single gene) disorders - will remain a major challenge."