By Dr. Richa Katiyar (MD – Fertility Specialist and Gynaecologist at Hope Fertility) in association with iGenetic Diagnostics
Prenatal tests and care are important for all pregnant women. However, it is all the more crucial for women who conceive after 35 years of age. The tests determine the likelihood of certain defects in the baby. This helps in counselling patients regarding decisions to continue the pregnancy and doing any additional tests required for confirmation of the diagnosis. These defects include genetic disorders like Down Syndrome, Patau Syndrome, Edward Syndrome, Sickle Cell Disease, Cystic Fibrosis, Tay-Sachs Disease, Muscular Dystrophy and Spina bifida (Neutral tube defect) among others.
Rapid advancements in medical sciences including diagnostics has resulted in better management of pregnancies, especially in older women. Healthy women deliver healthy babies. Apart from lifestyle changes for a healthy pregnancy, regular screening of the mother and foetus during pregnancy helps in timely interventions that can ensure the best outcome.
During the pregnancy, blood tests can be done to monitor the health of the mother by examining whole blood counts, and checking for sexually-transmitted diseases like HIV or Hepatitis B. Blood disorders that might potentially be detrimental to baby’s health can be determined at this time. The mother’s blood group is also reconfirmed and the Rhesus (Rh) factor is determined. If the mother is Rh negative (Rh-) and the father is Rh+, there is a chance that the baby may be Rh+. In such a case, the doctor will recommend a routine dose of anti-D immunoglobulin to avoid any complications that can be detrimental to the baby.
Additionally, there are tests scheduled at specific stages during gestation. These tests help in monitoring the pregnancy and help in better management of the pregnancy. This is particularly important if any of the parameters are not within healthy range.
First Trimester (Up to 13 Weeks of Pregnancy)
First-trimester screening includes ultrasound and maternal serum screening. Ultrasound is done to assess fetal nuchal translucency and to determine the presence of the nasal bone. Nuchal translucency screening is used to see if there is increased fluid or thickening in the back of the foetus’ neck. The nasal bone is not seen in babies with conditions like Down syndrome. This scan is generally performed between 11 and 13 weeks gestation. In this trimester, ultrasound is also used to determine the due date, examine the placenta, uterus, pelvis etc, and to diagnose an ectopic pregnancy or miscarriage.
Besides ultrasound, certain maternal serum markers are also assessed in the first trimester. In early pregnancy, abnormal levels of Pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG) are associated with increased risk of birth defects. In combination with ultrasound, these maternal blood tests help predict the likelihood of birth defects like Down syndrome and Edwards syndrome.
If the results indicate any abnormality, genetic counselling and additional tests like chorionic villus sampling or amniocentesis are recommended.
Chorionic Villus Sampling (CVS)
This test is done between 10 and 13 weeks of pregnancy. It involves taking a sample of the chorionic villus from the placenta through the cervix or abdominal wall. This tissue contains the same genetic material as the foetus. This can be then be tested for genetic defects.
Second Trimester (11-24 Weeks Of Pregnancy)
Second-trimester maternal serum screening is done between 15 and 20 weeks of pregnancy and involves multiple marker screening (either triple or quadruple marker screening). Levels of Alpha-fetoprotein (AFP) that is produced by the fetal liver vary during pregnancy. Abnormal levels may indicate an incorrect due date, foetal abdominal wall defects, Down’s syndrome or some other chromosomal abnormality, the presence of more than one foetus or an open neural tube defect like spina bifida. Levels of Estriol can be an indicator of foetal health. Other markers that are screened in this trimester are Inhibin and hCG.
At this stage, ultrasound (called as 18- to 20-week scan) is also performed to reconfirm the due date, look for abnormalities in the foetus, monitor its growth and activity, check the amount of amniotic fluid and blood flow patterns, and examine the cervix.
In combination with the first-trimester screen, second-trimester tests can predict any abnormalities in the foetus. In pregnancies where ultrasound and maternal serum screening tests are abnormal, an amniocentesis may be needed for an accurate diagnosis.
Amniocentesis
Amniocentesis is generally done between 15 and 20 weeks of pregnancy by inserting a long, thin needle through the abdominal wall and into the amniotic sac. A small amount of amniotic fluid is withdrawn. This fluid contains cells from the foetus. Any genetic abnormality in the foetus can be detected using these cells. AFP can be directly measured in this sample to determine if there is an open neural tube defect.
Third Trimester (Beyond 24 weeks Of Pregnancy)
Foetal Growth Scan
This test is to be done between 28 and 32 weeks of pregnancy. This is an Ultrasound and Doppler Scan test to determine the position of the foetus, monitor foetal growth and the position of the umbilical cord, measure the quantity of amniotic fluid, examine the placenta and to conduct a biophysical profile test.
Oral Glucose Tolerance Test or the Glucose Challenge Test
This test is usually done between 24-28 weeks. It is also known as OGTT, the test evaluates the mother’s ability to absorb and use glucose (sugar). This checks gestational diabetes. Gestational diabetes can lead to preeclampsia and high blood pressure.
Just Before Labour
Amniotic Fluid Index Test: This test determines the quantity of amniotic fluid in the water bag. Amniotic fluids protect the foetus from injuries if there is any blow to the stomach. It also protects the baby from infection and also lets the digestive system of the baby grow. Low amniotic fluid levels can harm the baby’s health.
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