PRENATAL TESTING12 August 2020
PRENATAL TESTING, THE BENEFIT OF EARLY ANTENATAL CARE
The prenatal period or antenatal period is the time from fertilization just until before birth. Prenatal testing are screening and confirmatory tests that are carried out during the prenatal period on the mother or product of conception (placenta, amniotic fluid) for the possible presence of a disease condition either on the mother or baby. This screening and confirmatory tests are called prenatal tests.
Generally, these tests are done early in pregnancy. They might be repeated in the course of the pregnancy. Hence, the importance of early antenatal care booking to benefit from these screening tests where possible. The availability of some prenatal test depends on the available laws in the country and the availability of diagnostic skill, technology and approved treatment protocol. Even where it is available, it is not mandatory.
So, based on your history and examination findings, your healthcare provider may recommend some antenatal testing for chromosomal abnormalities. In some countries, it is part of the routine testing for all pregnant women in early pregnancy. After counselling on what the conditions are, availability of screening or confirmatory test and the possible treatment available. These tests might be ordered. It is optional and you can choose not to participate.
PRINCIPLES OF PRENATAL TESTING
A screening test help categorize the patient into a low risk or high risk group. Further testing is carried out on those classified as high risk. There should be a balance between the potential benefits of a screening test to the harm it might cause in an otherwise healthy pregnancy. Hence, the principles of prenatal testing as reported by Wilson and Jungner (1968).
- The health condition screened for must be an important health problem.
- There should be an accepted treatment for pregnant women and babies identify with the disease condition.
- There should be available facility and skill for diagnosis and treatment.
- There should be a recognizable dormant or early symptomatic stage.
- The natural history of the condition which includes it development from a dormant to a declared disease, should be adequately understood.
- There should be a suitable test or examination.
- The test should be acceptable to the population.
- There should be an agreed policy on whom to treat as a patient.
- The cost of diagnosis and treatment of patients should be economically balanced in relation to possible expenditure on medical care as a whole.
- Case‐finding should be a continuing process and not a ‘once and for all’ project.
PRENATAL TESTING FOR GENETIC ABNORMALITIES
Genes are a portion of the chromosome involve in the transfer of traits from parents to their children. Abnormalities in the number or structure of a chromosome can result in diverse disease conditions. Common amongst them include Down’s syndrome, Edward syndrome, Patau syndrome, Turner’s syndromes and a lot of other disease conditions. Nature has a way of taking care of things that it only allows the fittest to survive most of the time.
Thus, explaining the reason why a lot of these pregnancies abort spontaneously. Sometimes, before the woman even realizes she is pregnant. Some of these pregnancies with genetic abnormalities continue and the babies are delivered alive. Most of them have intellectual disability and cannot live an independent life thus, a burden to both the family and the healthcare system.
Hence, in countries where abortion is legal, such pregnancies are terminated if the couple do not want to continue with the pregnancy.
THE SCREENING TESTS
First trimester combined screening involves the use of ultrasound scan and maternal blood to screen for chromosomal abnormalities. A fetal nuchal translucency of ≥ 3.5mm as seen on scan with a reduce pregnancy associated plasma protein -A(PAPP-A) and increased free beta human chorionic gonadotropins (B-HCG) in maternal blood is associated with Down’s syndrome.
However, an increased fetal nuchal translucency with reduced PAPPA-A and B-HCG is associated with Edward, patau’s and Turner’s syndromes. Non-invasive prenatal testing using cell free fetal DNA obtain from the maternal blood can also be used for screening for Down’s syndrome.
THE CONFIRMATORY TEST
After a positive screen, a confirmatory test using cytogenetic studies can be carried out such as karyotyping. Karyotype which could be rapid or full karyotype, study the number and structure of the chromosome. This test reveals abnormalities depending on whether it is the full karyotype or rapid karyotype. The full karyotype is a comprehensive study and takes about 2 weeks to get the result.
Moreover, the rapid karyotype is limited to abnormalities in a few chromosomes implicated in Down’s, Edward, patau syndrome and also abnormality of the sex chromosomes. It takes about 48hours to get the result. Samples for karyotyping can be gotten via amniocentesis or chorionic villus sampling. These procedures are recommended early in the first trimester, about 11weeks of pregnancy for chorionic villus sampling and 15weeks for amniocentesis.
Just like amniocentesis, chorionic villus sampling is associated with some complications such as perforation of the intestine, bleeding and pregnancy loss. There is no need looking for something you do not want to act upon and get yourself worked up throughout the pregnancy period. If you are a pro-lifer, prenatal testing for chromosomal abnormalities might not be for you.