Published by the Students of Johns Hopkins since 1896
September 19, 2020

Scientists create new prenatal blood test

November 19, 2015

RICMART 01/CC-BY-SA-4.0 This informational blood test can reduce the risk of miscarriage.

By TONY WU Senior Staff Writer

Parents often wonder about the sex and medical condition of their unborn child after the news of a pregnancy. Ultrasound images are currently used to allow parents to peer into the womb and reveal the baby’s sex by capturing images of its external genitalia if taken at the right time and angle. However, these predictions are not precise due to the low image qualities and the positioning of the baby. With the drawbacks of ultrasound images and the dangers of the more invasive amniotic fluid test (AFT) in mind, a more accurate and comprehensive fetal test is currently under development. Researchers at Plymouth Hospital and Plymouth University recently created an alternative to the AFT that can also detect birth defects. This improved procedure reduces the risk of miscarriage by using maternal blood samples rather than amniotic fluids. This represents the first use of a blood test to determine fetuses’ sex, blood type and health conditions. AFT typically uses a needle that penetrates the abdominal and uterine wall of the pregnant mother. Once the needle reaches the amniotic sac, the doctor extracts about 20 milliliters of the fetal cell, containing amniotic fluid. The cells are separated, and the chromosomes are examined for defects. In most cases the AFT does not harm the fetus. However, the mother suffers a miscarriage in about one percent of the tests. The risk increases substantially when the test is performed before the 15th week of the pregnancy. This is because the invasive extraction of amniotic fluid can cause injury to the fetus. Doctors only perform amniocentesis when they suspect serious birth defects based on their analysis of ultrasound images because of these risks. Another alternative to AFT is chorionic villus sampling, which can also cause miscarriages especially if a fetus is smaller than average. This procedure involves removing some placental tissue through either the abdominal wall or the cervix of the mother. In contrast, the test developed by researchers examines the blood that is circulating between the fetus and the mother. This carries metabolites, hormones and DNA from the fetus into the maternal blood. Researchers can run DNA sequencing tests by extracting the fetal DNA from these blood samples, which provides them with information about the developing fetus including its sex and potential medical conditions. Scientists have been able to amplify the DNA in samples that contain low quantities of it through a process called digital polymerase chain reaction (PCR). Scientists can make multiple copies of a small chain of DNA through PCR, which can improve their ability to analyze the DNA. Doctors can inform their patients about the conditions of their child more accurately by utilizing this new technique. This can prove especially useful when the child suffers a debilitating disease such as spina bifida (a spinal defect that causes the spinal bones to form improperly around the spinal cord). Patients with spina bifida may have problems with walking and bladder control. This blood test could reveal chromosomal defects such as Down Syndrome or Duchenne muscular dystrophy for other patients. “The technique represents a comparatively low-risk method for the early identification of a number of conditions, which in turn will aid earlier diagnosis and possible therapies to the potential benefit of both mother and child,” Neil Avent, the study’s lead author and a professor at Plymouth University School of Biomedical and Healthcare Sciences, told Science Daily. Overall this new procedure can provide parents with information about their unborn children without posing as much of a risk to the health of fetuses as existing tests do.

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