Screening

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 individual developing certain complications during pregnancy including pre-eclampsia or of 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, VPA, SSRI, CBZ)

Prenatal screening is not diagnostic. Screening does not determine with certainty whether a baby will have a birth defect or chromosome abnormality, nor can it with certainty detect all individuals who will develop Pre-eclampsia. It only calculates the risk—high or low; positive or negative– that an abnormality may occur. If the risk is higher than a predetermined acceptable level, the pregnant patient will usually be sent for further diagnostic testing – such as amniocentesis or chorionic villus sampling or will be monitored more closely in prenatal care.

For most, prenatal 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 individuals who undertake prenatal screening are found to be high risk and are sent for diagnostic testing.

What is Prenatal Screening Software?

Prenatal screening software considers details of the pregnant patient, such as age, parity status, and family history of conditions, and incorporates 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. Other conditions such as Trisomy 13 and Smith-Lemli-Opitz syndrome can be included in prenatal screening.

Benetech PRA can also be used to screen a pregnant patient’s risk for developing Pre-eclampsia.

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”. Conversion of an assay result to a MoM allows for an effective and simple way to normalize an individual marker value with the entire population being screened.