Introduction:
Prenatal tests are medical tests that a woman may be provided throughout her pregnancy to learn more about her and her baby’s health. For prenatal diagnosis and fetal therapy, fetal medicine is a difficult task that requires a multidisciplinary team.
Prenatal testing may be beneficial in selecting different pregnancy options or special management of the pregnancy and birth to improve the baby’s outlook. Depending on the mother’s phase of pregnancy and the health condition, different methods of prenatal testing are available and can be employed accordingly.
These prenatal tests can be performed to monitor and know the health issues in the infant, such as:
Birth defects
- These are medical problems that exist at the time of birth. They alter the appearance or function of one or more physical parts.
- Birth defects can affect your overall health, as well as how your body develops and functions.
Genetic and chromosomal conditions
Changes in genes and chromosomes are too responsible for these disorders. A gene is a molecule found in the cells of your body that stores instructions for how your body grows and functions. The structure in cells that holds genes is called a chromosome.
Cystic fibrosis (commonly known as CF), sickle cell disease, and cardiac abnormalities are all genetic diseases. Down syndrome is a common chromosomal disorder. These conditions can be passed on from one generation to the next, or they can develop on their own.
Types:
Prenatal screening tests
Both the first and second trimesters of pregnancy are suitable for screening tests. An ultrasound check and a sample of the mother’s blood are required for first trimester screening, whereas only a blood sample is required for second trimester screening. Some women may be offered “integrated” or “combined” screening, which is a combination of first and second trimester screening and cell-free DNA testing. The findings of the blood tests and ultrasounds are then coupled with maternal variables such as age and weight to determine the likelihood of particular chromosomal disorders in the present pregnancy.
Within a week, screening results are usually available, and individuals who have a positive result are offered diagnostic testing. The rate of detection for screening tests differs depending on the test type. In addition, this test can screen the fetus for aneuploidy; defects of the brain and spine called neural tube defects (NTDs); and some defects of the abdomen, heart, and facial features.
Prenatal diagnostic tests
These tests can determine whether or not the foetus has specific abnormalities. The two types of diagnostic tests are chorionic villus sampling (CVS) and amniocentesis. Cells from the fetus or placenta acquired these assays can determine with greater than 99.9 percent accuracy whether or not a developing baby has a chromosomal difference. Tests for certain genetic abnormalities must be obtained in advance.
Between 10.5 and 13.5 weeks of pregnancy, a CVS procedure is conducted. A doctor collects a tiny tissue sample from the placenta during the operation by either putting a thin needle through the woman’s belly or introducing a small catheter through the cervix. The procedure employed is influenced by the baby’s and placenta’s location.
From the 15th week of pregnancy ahead, amniocentesis is undertaken. A tiny needle is introduced into the amniotic sac via the woman’s belly to remove a small sample of fluid from surrounding the growing baby during amniocentesis.
Cells obtained from either process can be used for chromosomal analysis or other genetic assays when necessary. The findings of chromosomal analysis normally take two weeks, while other genetic testing may take longer, depending on what test was ordered.
There is a risk of miscarriage connected with diagnostic test methods, which is estimated to be up to 1% for CVS and less than 1% for amniocentesis.
Preimplantation genetic Screening/diagnosis (PGS): state of the art
It is a technique for genetically analysing embryos before they are implanted into the uterus that can be used as an early pre-natal diagnosis to ensure a pregnancy free of any chromosomal abnormalities. The goal of pre-implantation genetic diagnosis is to determine the genetic status of cells (typically single cells) biopsied from oocytes/zygotes or in vitro-created embryos during assisted reproductive treatment.
Goal and objective:
Since the initial identification of the molecular structure of DNA, the scene of genetic testing and screening has changed significantly.
- Identify specific threats to the fetus
- Make a pregnancy assessment
- Consider the several prenatal diagnostic options.
- If desirable and possible, diagnose the fetus
- Inform family members about the diagnosis, expected outcomes, and potential treatments.
- Counsell about the dangers, advantages, and unknowns.
- consult through family issues.
- Conduct a risk assessment for additional members of the family.
- Assist with psychosocial issues and follow-up
Who will be benefits from prenatal diagnosis?
- People who live in families that are at a higher risk of developing a genetic condition.
- A family history of chromosomal disorders or genetic diseases
- Chromosome abnormalities are more common in older women (> 35).
- Maternal illness is linked to a higher incidence of birth abnormalities (diabetes, phenylketonuria)
- Pregnancy exposure to a known teratogen
- Screening tests or ultrasounds that are abnormal
- Women who are worried or concerned
Reliability and accuracy:
There is the chance of false-positive and false-negative results with any form of testing. A false-positive result is a screening test result that indicates the presence of a condition when none exists. A false-negative result is a screening test result that shows there isn’t an issue when there is. The rates of false-positive and false-negative results for each test can be obtained from your health care provider.
Current practice, emerging advanced, and ethical issues:
- Prenatal screening programs, as they are now given in most Western countries, consist of tests that are identical. To begin, pregnant women are provided a risk assessment test for significant aneuploidies. Invasive diagnostic tests, which carry a risk of miscarriage, are offered if there is a higher risk. For many years, the only method of ultimate diagnosis was traditional karyotyping. Furthermore, a number of foetal ultrasound scans are available to detect serious congenital defects, but the same scans also provide useful information for the best possible pregnancy and delivery assistance. Microarrays, which may detect a significantly larger variety of abnormalities than karyotyping, and non-invasive prenatal testing (NIPT), which allows for a significant reduction in the frequency of invasive tests for aneuploidies, are two recent advancements in prenatal screening.
- Owing to the rapid breakthroughs in genomics, properly incorporating new genomic testing into prenatal clinical practice remains difficult. Next-generation sequencing technology can be used to run genomic analyses on fetal samples collected through amniocentesis or chorionic villus sampling. Karyotype and CMA are two of the most used genetic tests today. In clinical adult and paediatric medicine, whole exome sequencing (sequencing the exons or protein-coding sections of the genome) is beginning to find a role.
- Finally, the rapid use of genetic tests in clinical practice demands tight coordination and communication among research laboratories, commercial laboratories, professional associations, and doctors. Every attempt should be made to bring these organizations together in order to promote women’s science and care.
Key points:
- Prenatal testing can assist to understand out how mother and fetus doing during pregnancy.
- During pregnancy, some prenatal tests, such as a blood pressure check and a urine test, are repeated numerous times.
- Other prenatal diagnostics, such as ultrasounds or blood tests, are performed less frequently.
- Some prenatal tests look for health issues in your baby, such as birth abnormalities or genetic diseases.
References:
- Vora NL, Wapner RJ. Introducing new and emerging genetic tests into prenatal care. Semin Perinatol. 2018 Aug;42(5):283-286. doi: 10.1053/j.semperi.2018.07.004. Epub 2018 Jul 26. PMID: 30115457; PMCID: PMC6370457.
- de Jong A, Maya I, van Lith JM. Prenatal screening: current practice, new developments, ethical challenges. Bioethics. 2015 Jan;29(1):1-8. doi: 10.1111/bioe.12123. PMID: 25521968.
- American College of Medical Genetics www.acmg.net.
- Semin Perinatol. 2018 Aug;42(5):303-306. doi: 10.1053/j.semperi.2018.07.019
- Wang J, Tang XX, Zhou Q, Yang S, Shi Y, Yu B, Zhang B, Wang LL. Int J Womens Health. 2021 Sep 22; 13:879-888. doi: 10.2147/IJWH.S324529.
- American College of Obstetrics and Gynecology www.acog.org.