First Trimester Combined Test

The first trimester combined test is a prenatal screening test conducted during the first trimester of pregnancy, typically between 11 and 14 weeks. This test is designed to assess the risk of the fetus having certain chromosomal abnormalities, most notably Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). The combined test includes two main components:

  1. Blood Test:
    1. Pregnancy-Associated Plasma Protein-A (PAPP-A): Lower than normal levels of PAPP-A in the mother’s blood have been associated with a higher risk of chromosomal abnormalities.
    2. Human Chorionic Gonadotropin (hCG): This hormone, produced by the placenta, can be higher or lower than average in pregnancies affected by certain chromosomal conditions.
  2. Nuchal Translucency (NT) Ultrasound Scan:
    1. During the ultrasound, a measurement is taken of the nuchal translucency, which is a fluid-filled space at the back of the fetus’s neck. A thicker nuchal translucency can be a sign of chromosomal abnormalities or other developmental issues.

The results from the blood test and the NT scan are combined with the mother’s age and other factors to assess the risk of the fetus having a chromosomal abnormality. The test provides a risk assessment rather than a definitive diagnosis. If the risk is high, further diagnostic tests, such as chorionic villus sampling (CVS) or amniocentesis, might be recommended for a conclusive diagnosis.

Advantages of the First Trimester Combined Test:

  • It provides early information about the risk of certain chromosomal abnormalities.
  • Being non-invasive, it poses no risk to the fetus.
  • It can help expectant parents make informed decisions about whether to proceed with more definitive but invasive diagnostic tests.

Limitations:

  • It is a screening test and not diagnostic. This means it can’t confirm whether the fetus has a chromosomal abnormality; it only indicates the likelihood or risk.
  • There is a chance of false positives (indicating a problem when there isn’t one) and false negatives (failing to detect an existing problem).

The first trimester combined test is a standard screening option offered to many pregnant women, especially those without known risk factors for chromosomal abnormalities. It’s a part of the range of prenatal care options available to ensure the health and wellbeing of both the mother and the fetus