Antenatal testing is a term that refers to various tests and procedures that are performed during pregnancy to monitor the health and well-being of the mother and the baby. Antenatal testing can help detect and prevent potential complications, such as preterm birth, foetal growth restriction, preeclampsia, gestational diabetes, chromosomal anomalies and stillbirth.

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Two Main Categories of Antenatal Testing

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Antenatal testing can be divided into two main categories: screening tests and diagnostic tests. Screening tests are used to estimate the risk or likelihood of having a certain condition, but they do not provide a definitive diagnosis. Diagnostic tests are used to confirm or rule out a condition with a high degree of accuracy, but they may carry some risks for the mother or the baby.

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Screening tests are usually offered to all pregnant women as part of routine prenatal care, while diagnostic tests are usually reserved for women who have a positive screening result, a personal or family history of a genetic disorder, or other risk factors.

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Some of the common screening tests that are performed during pregnancy include:

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• Blood tests: These are used to check the mother's blood type, Rh factor, iron level, glucose level, antibody level, and infection status (such as hepatitis B, syphilis, HIV, rubella and varicella). Blood tests can also be used to screen for chromosomal anomalies (such as Down syndrome, Edwards syndrome and Patau syndrome) by measuring certain proteins and hormones in the mother's blood (such as alpha-fetoprotein, human chorionic gonadotropin, unconjugated estriol and inhibin A).

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• Urine tests: These are used to check for signs of urinary tract infection, proteinuria (excess protein in the urine), glycosuria (excess sugar in the urine), and ketonuria (excess ketones in the urine). These conditions may indicate an increased risk of preeclampsia, gestational diabetes or dehydration.

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• Ultrasound scans: These are used to visualise the baby's anatomy, growth, position, movement and heart rate. Ultrasound scans can also be used to measure the amount of amniotic fluid around the baby (amniotic fluid index), the length of the cervix (cervical length), and the blood flow in the umbilical cord and placenta (Doppler studies). Ultrasound scans can also be used to screen for neural tube defects (such as spina bifida and anencephaly) by measuring the nuchal translucency (the thickness of the fluid-filled space at the back of the baby's neck) or by performing an anatomy scan (a detailed examination of the baby's organs and structures).

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• Nonstress test (NST): This is a method of assessing foetal well-being by observing the foetal heart rate response to foetal movement. A foetal monitor is used to record contractions and foetal heart rate. A normal result is when the foetal heart rate increases by at least 15 beats per minute for at least 15 seconds in response to foetal movement.

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• Modified biophysical profile (MBPP): This is a combination of NST and amniotic fluid index. It is used to evaluate foetal well-being and placenta function in certain high-risk pregnancies.

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Some of the common diagnostic tests that are performed during pregnancy include:

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• Chorionic villus sampling (CVS): This is a procedure that involves taking a small sample of tissue from the placenta (the organ that connects the mother and the baby) for genetic analysis. CVS can be performed between 10 and 13 weeks of gestation. It can diagnose chromosomal anomalies and some genetic disorders with a high degree of accuracy, but it carries a small risk of miscarriage or infection.

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• Amniocentesis: This is a procedure that involves taking a small sample of fluid from the amniotic sac (the fluid-filled sac that surrounds the baby) for genetic analysis. Amniocentesis can be performed between 15 and 20 weeks of gestation. It can diagnose chromosomal anomalies and some genetic disorders with a high degree of accuracy, but it carries a small risk of miscarriage, infection or injury to the baby.

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• Cordocentesis: This is a procedure that involves taking a small sample of blood from the umbilical cord (the cord that connects the baby and the placenta) for genetic analysis. Cordocentesis can be performed after 18 weeks of gestation. It can diagnose chromosomal anomalies and some genetic disorders with a high degree of accuracy, but it carries a small risk of miscarriage, infection, bleeding or injury to the baby.

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Antenatal testing is an important part of your pregnancy care and can help you and your health professionals make informed decisions about your pregnancy and birth. However, antenatal testing is not mandatory and you have the right to accept or decline any test or procedure that is offered to you. You should discuss the benefits, risks and limitations of each test or procedure with a health professional and make a shared decision that is best for you and your baby.

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Sources

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- Debbo Africa: debbo.africa

- Indications for Outpatient Antenatal Fetal Surveillance | ACOG. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2021/06/Indications-for-outpatient-antenatal-fetal-surveillance

- Antenatal Testing Center | UCSF Health. https://www.ucsfhealth.org/clinics/antenatal-testing-center

- Routine antenatal tests - blood tests, scans, swabs | healthdirect. https://www.healthdirect.gov.au/routine-antenatal-tests

- Antenatal tests: chromosomal anomalies | Raising Children Network. https://raisingchildren.net.au/pregnancy/health-wellbeing/tests-appointments/antenatal-tests-anomalies