May 2, 2012 -- Researchers say they've found a way to identify the father of a baby as early as the eighth week of pregnancy.
The new method, reported in the New England Journal of Medicine, uses fetal DNA isolated from the mother's blood.
The test has already been used to prove an affair in a murder trial, and experts say it has other significant medical and legal applications.
"The technology is extremely important and really a very, very significant step forward for medical prenatal diagnosis," says Peter Benn, PhD, director of the diagnostic medical genetics laboratories at the University of Connecticut Health Center in Farmington. He was not involved in the research.
"That technology will allow genetic disorders to be identified without going through amniocentesis or chorionic villus sampling. That's a very important and useful step forward because those tests are not without some degree of risk to the fetus," Benn says.
Amniocentesis, in which a small sample of fluid that surrounds the fetus is removed and analyzed, and chorionic villus sampling, in which a small piece of tissue from the placenta is removed and analyzed, can cause infections, miscarriages, and birth defects. These tests are not able to be done before 10 to 15 weeks of pregnancy.
"Before we could only rely on tests that were invasive and could only be done later in pregnancy," says Jill Rabin, MD, chief of ambulatory care, obstetrics, and gynecology at Long Island Jewish Medical Center in New Hyde Park, N.Y.
"Here you have a blood test with the possibility of giving you an answer so that a woman can decide whether to proceed with a pregnancy or not based on the results of a noninvasive test. That is, right there, a tremendous utility," says Rabin, who was not involved in the research. "This is really cutting-edge stuff. It's very exciting."
Finding Fetal DNA in Mom's Blood
The new test overcomes several significant obstacles.
The first is that while researchers have long known that fetal DNA is present in the mother's blood, they believed it was floating around in such tiny amounts that it was almost impossible to find and analyze.
One of the reasons it was thought to be so rare, says researcher Ravinder Dhallan, MD, PhD, chairman and chief executive of Ravgen Diagnostics in Columbia, Md., is that the mother's blood cells easily burst when blood samples are drawn, which dilutes the fetal DNA.
By mixing a fixative agent into the blood sample, Dhallan says he was able to isolate enough fetal DNA so that it could be tested.
"What we realized was that if you add any fixative, it makes the mother's white blood cells, instead of being like water balloons that easily burst, they become more like ping pong balls that are stiff and won't burst," says Dhallan. "Now you've got 25% fetal DNA instead of 1% fetal DNA" in the blood.
By looking at the baby's DNA, researchers are able to spot places where the gene sequences are different from the mother's by only one letter. That letter will match the father's DNA. A sample of DNA from a suspected father can then confirm or exclude paternity.
When researchers tested 30 blood samples from biologic mothers and fathers who were grouped with unrelated men, they say they were able to correctly identify paternity in every case.
According to Ravgen's web site, the technology was used in 2009 to help prove that Michael A. Roseboro, who was on trial for his wife's murder, had fathered a baby with another woman. Prosecutors argued that the affair was motive for the murder.
Dhallen says he was motivated to develop the paternity test after being contacted by women who were eager to prove paternity and uncertain about whether to continue their pregnancies after situations involving violence, including rape.
"There are so many situations where people need to identify the paternity before the baby is born that are social, medical, and legal," he says.