Benetech PRA Calculates the Risk That an Abnormality May Occur
What is Prenatal Screening?
Prenatal screening is the process of determining the chances of a pregnant woman having a baby born with a chromosomal abnormality, or birth defect. The risk is calculated using a number of factors.
Factors depend on the condition being screened for and the screening practices of each laboratory, and may include one or more of the following:
- the age of the mother at the time of delivery
- population prevalence of the condition
- the measurements of a number of chemical substances found in the mother’s blood at various times during the pregnancy
- specific measurements of the fetus taken using ultrasound
- sub-populations (IDDM, smoking status, IVF)
Prenatal screening does not determine whether or not a baby has a birth defect. It only calculates the risk that an abnormality may occur. If the risk is higher than a predetermined acceptable level, the pregnant mother will usually sent for further diagnostic testing – such as amniocentesis or chorionic villus sampling.
For most women, prenatal genetic screening involves two blood tests, one done in the first trimester and one in the second trimester, and an ultrasound done in the first trimester.
Approximately one in twenty, or 5%, of pregnant mothers who undertake prenatal screening are found to be high risk and are sent for diagnostic testing.
What is Prenatal Screening Software?
Prenatal screening software takes the age of the mother and the measurements that were observed in the blood tests and the ultrasounds and runs them through published algorithms to calculate risk for that pregnancy. Typically, doctors will take blood samples and ultrasound measurements in their offices and send the results to a lab for processing. That lab will take the measurements from the blood and ultrasound and enter the figures into the prenatal screening software program. The software then produces a report which is sent back to the doctor for discussion with the patient.
What conditions does prenatal screening screen for?
The most common abnormalities that are screened for are Down syndrome, Trisomy 18 and Open Spina Bifida.
What is a MoM?
The term MoM stands for Multiple of Median. The MoM is a measure of how far an individual test result deviates from the median (middle) value of a large set of test results obtained from unaffected pregnancies. For example, if the median AFP result at 16 weeks of gestation is 30 ng/mL and a pregnant woman’s AFP result at that same gestational age is 60 ng/mL, then her AFP MoM is equal to 60 divided by 30 (60/30) or 2.0. In other words, her AFP result is 2 times higher than “normal.”