Researchers have developed a non-invasive way to check for birth defects in women who are no more than five weeks pregnant. The test could do away with potentially harmful methods — collecting either fluid or a small tissue sample from the growing fetus's placenta or sac — now used to screen for congenital defects in the growing fetus. More than 6,000 congenital diseases, including sickle cell anemia and Down syndrome, are caused by a single gene mutation. Many of the genetic diseases cause pediatric hospitalizations or deaths. The new technique could lead to early identification and treatment of some defects, including metabolic disorders, while the baby is still in the womb. In looking for a safer test, doctors considered using the Pap smear, where a small sample of cells is scraped from the lower part of a woman's womb, called the cervix, for examination. The placenta, which envelops and nourishes the fetus, sheds an unborn baby's cells into the mother's body. Those cells can then be collected by a Pap smear. However, the mother's cells are mixed in with those of the growing fetus. Molecular biologist Sascha Drewlo and his colleagues at Wayne State University in Detroit, Michigan, found a way to separate the cells to look for disease-causing mutations in the unborn baby's DNA. "As you can imagine, all those cells are covered with maternal DNA and this can mask a lot of the results in the beginning,” Drewlo said. “And we are very happy that we were able to solve this important problem." In a study involving 20 healthy women who were between five and 19 weeks pregnant, Drewlo and his colleagues compared maternal DNA to samples of tissue taken from the placenta itself, using a method that measured expression of a protein by the placental cells, called trophobasts. The researchers were able to separate the baby’s DNA from the mother’s. Then, they applied the screening method to cells obtained in Pap smears. In every case, the scientists were also able to distinguish the mother’s cells from those of the fetus. The study was published in the journal Science Translational Medicine. Called a proof-of-principle, the work showed that the screening test could be performed in women no more than five weeks pregnant, without risk to the fetus. Drewlo said Pap smears are already routinely performed in non-pregnant women to screen for cancer, and genetic tests of fetal cells obtained in a Pap smear would look for very specific mutations for diseases. Drewlo said it shouldn't be long before doctors are using the procedure to check for disorders in the developing fetus. The technology is very established, he says, "we are just adjusting it for our particular needs." Drewlo said the next study will use cervical swabs to look for disorders in the growing fetus.