Prenatal Tests Split Across Three Trimesters of Pregnancy
Prenatal tests are a crucial part of a healthy pregnancy, providing expectant parents with valuable insights into the health of both mother and baby. These tests are performed throughout the three trimesters of pregnancy, each serving a unique purpose.
First Trimester (Weeks 1–13):
The first trimester focuses on dating the pregnancy and screening for genetic risks. Key tests include the Dating Scan, performed around 6 to 14 weeks to confirm pregnancy viability and estimate gestational age. The Nuchal Translucency (NT) Scan, carried out at 11 to 13 weeks, measures fluid at the back of the fetal neck to assess the risk of chromosomal abnormalities.
The Combined First-Trimester Screening (Double Marker Test + NT scan) is a blood test measuring pregnancy-related markers combined with the NT scan to screen for chromosomal disorders. For a more definitive diagnostic test, Chorionic Villus Sampling (CVS) can be performed between 10-13 weeks to collect placental tissue for genetic testing when indicated.
A Detailed First Trimester Ultrasound (DFTU) may be performed at 12-13 weeks, especially for high-risk pregnancies, to detect structural fetal anomalies early.
Second Trimester (Weeks 14–27):
The second trimester emphasises anatomical evaluation and additional risk assessment. The Triple or Quad Marker Test, performed between 14-20 weeks, measures AFP, hCG, estriol, and inhibin-A to assess risks for neural tube defects and chromosomal abnormalities.
The Anomaly Scan / Morphology Scan, carried out at 18-22 weeks, evaluates detailed fetal anatomy and detects structural anomalies. Amniocentesis, an invasive diagnostic test performed after 15 weeks, may be carried out for fetal genetic analysis if indicated by abnormal screening or family history.
Screening for gestational diabetes and anemia is usually done at 24-28 weeks to assess maternal health.
Third Trimester (Weeks 28–40):
The third trimester monitors fetal well-being and growth. A Third Trimester Ultrasound is typically done between 32-36 weeks to monitor fetal growth, presentation, amniotic fluid volume, and placental position. Cordocentesis (Percutaneous Umbilical Blood Sampling) is a rare invasive test to obtain fetal blood in specific cases for diagnosis or treatment.
Additional Tests:
Other tests include the Non-stress Test, which measures the baby's heart rate when the mother experiences uterine contractions, ensuring the baby receives an adequate amount of oxygen from the placenta during labour. This test is performed several times, including during labour and delivery.
The Multiple Marker/Quadruple Screen Test during pregnancy for birth defects screens the baby for Down syndrome and certain neural tube defects. This test is performed between the 16 and the 18 week of pregnancy.
Non-invasive Prenatal Screening uses a blood sample to look at the DNA from the placenta and identify if the baby is at risk of genetic conditions. This test is performed during labour as you deliver your baby.
Foetal Doppler ultrasound is used to measure the blood flow in the baby's veins and the overall health of the foetus. This screening test is performed between the 24 and 28 week of pregnancy.
The Cystic Fibrosis (CF) test may be performed with saliva or a urine sample to determine who is the carrier of the condition. The test is performed before the 20 week of your pregnancy.
Urine tests are performed to detect gestational diabetes, preeclampsia, infections, and other issues. The GBS test is performed between the 35 and the 37 week of pregnancy.
Other Tests:
- Pap smear detects signs of cervical cancer using cells swabbed from the cervix.
- STD tests include a blood test to detect the HIV virus that causes AIDS, which can seep into the placenta during or before delivery and infect the foetus.
- Abdominal scan examines the health of the organs in the abdomen, including the liver, gallbladder, pancreas, kidneys, appendix, intestines, and spleen, and can also provide a glimpse of the growth and development of the baby.
- Transvaginal scan examines the cervix, fallopian tubes, vagina, uterus, and ovaries and can check for any abnormalities in the placenta, monitor fetal heartbeat, check for any abnormal bleeding, and check for any complications in the cervix.
- Electronic foetal heart monitoring tracks your baby's heart rate during pregnancy, labour, and delivery to determine your baby's well-being. This test can be performed during the third trimester.
- Integrated or Sequential Screening uses a combination of ultrasound images of the baby's neck and the blood tests to determine the risk of Down syndrome, spina bifida, brain disorder, and spinal cord disorder. The first test of Integrated or Sequential Screening takes place between the 11 and the 14 week, and the second one between the 16 and the 18 week.
Understanding the various prenatal tests available can help expectant parents make informed decisions about their healthcare during pregnancy. It's essential to discuss these options with your healthcare provider to determine the most suitable tests for your unique situation.
