Prenatal Tests That Every Woman Should Undergo Before Planning a Pregnancy

Prenatal tests are performed before and during early pregnancy to assess mother and her baby's health. They can discover conditions that, if not treated, can put a baby at risk for complications such as preterm birth. Tests can also assist doctors in detecting birth defects or chromosomal abnormalities. Some prenatal tests are just screening tests, revealing the likelihood of a disease. Others are diagnostic tests that determine whether or not a foetus has a specific condition. A diagnostic test is occasionally performed after a screening test. The WHO guidelines indicate that every woman should be at least screened for the common chromosomal aneuploidies.

According to Dr. Dipanjana Datta, PhD, PDF (USA), Redcliffe Labs, the basic screening involves serum maternal markers at specific gestational weeks along with ultrasound markers, which can predict risk for common chromosomal aneuploidies like DOWN Syndrome, trisomy 18, and trisomy 13. Additionally, there are a few countries/specific communities where screening for common paediatric disorders can also be done. These tests are based on the population prevalence of the disorder and can also be specific for some communities. For example, we screen for thalassemia in this part of the world as it is prevalent.

Types of Prenatal Testing

Prenatal testing is classified into two types:

Screening tests

Prenatal screening tests can tell you whether your baby is more likely or less likely to develop certain birth problems, many of which are inherited. These testing include blood tests, ultrasounds, and prenatal cell-free DNA screening.

Prenatal screening tests are often performed in the first or second trimester. Screening tests cannot provide a conclusive diagnosis. If the findings show an elevated risk for a genetic disorder, your doctor will discuss your options for a diagnostic test to confirm the diagnosis.

• Depending on the risk estimation, further tests can be planned.
• If the combined risk of maternal and ultrasound markers comes as high risk, like around 1 in 100 or greater, then an invasive CVS or amniocentesis should be planned.
• For people with intermediate risk, NIPT can be offered, which is a test that can pick up aneuploidies with varying sensitivity from the maternal blood itself.
• If USG or maternal serum markers indicate an ONTD, then further USG and genetic testing like CMA or exome seq can be offered.
• Even at times, there can be indications in USG like structural anomalies in the fetus.
• Depending on the type of anomalies and indications, invasive tests like CMA and/or exome seq can be planned.

Diagnostic Tests

If a screening test reveals a potential problem, or if your age, family history, or medical history puts you at higher risk of having a baby with a genetic disease, you may want to pursue an invasive prenatal diagnostic test. The only way to be certain of a diagnosis is to do a diagnostic test. 

What Tests Are Needed During Pregnancy?

You must consult your gynaecologist before planning a pregnancy. Your doctor will take a full history of your current health and family history of medical conditions. They will inquire about any disorders in both families as well as pertinent information about your previous pregnancies. The doctor will also go through your prescriptions, immunizations, and supplements.

Genetic Screening

At times, there can also be an indication for additional advanced genetic screening before planning a pregnancy. India is characterised by multiple endogamous populations where marriage happens inside a community. There also prevalence of consanguinity in some parts of our social structure. These lead to an accumulation of deleterious genetic traits within the community or that family, contributing to the high prevalence of recessive gene alleles, which translates into genetic diseases. 

A family history of unknown new born or adult death, any history of congenital hearing or vision loss, cardiac or kidney disorders before the age of 30 years, with a history of epilepsy, intellectual retardation, neurodevelopmental/neuromotor delay, or recurrent pregnancy loss should also be investigated. In such cases, genetic counselling helps in informed decision making.

What Tests Will You Need Before You Become Pregnant?

Your doctor will prescribe certain tests for you to make sure that you and your partner are healthy before you embark on a pregnancy. These may include your blood count, blood group, screening for diabetes, thyroid disease, and thalassemia, STDs, and infections. You will also need a Rubella test to check if you are immune to German measles. German measles or Rubella infection (this is a mild flu-like infection with a rash) in the first three months of pregnancy can cause serious harm to the baby’s brain, heart, eyes, and ears. Therefore, it is important to have the rubella blood test before pregnancy to determine whether you need the rubella vaccination. You should have this injection at least 1 month before you start trying for a pregnancy. Additional genetic screening is recommended if there is a family history that is significant.

Tests During Pregnancy

Routine tests such as blood pressure, blood tests and urine tests are performed numerous times during pregnancy.

• First Trimester- The tests during first trimester (11- 13 weeks) can detect the risk to the fetus with certain birth defects such as Down syndrome, heart defects.  The tests involve fetal ultrasound and mother’s blood tests.
• Second trimester- Tests screen for congenital anomalies in the developing baby. These tests are blood tests known as multiple markers. A fetal ultrasound called the anomaly scan (performed in around 20 weeks gestation) can pick up such anomalies with a high detection rate.  A cardiac evaluation for the fetus is also suggested around 22 -24 weeks. 

Furthermore, ultrasounds are done from time to time for analysing fetal growth, structural abnormalities in baby and evaluate the due date. Also, other essential tests comprise of fetal monitoring, amniocentesis, glucose testing, and Group B Strep culture.

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