Second Trimester Pregnancy Screening
What is being analysed?
Second trimester screening during pregnancy involves analysing maternal serum markers and ultrasound findings to assess the risk of chromosomal abnormalities such as Down’s syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13), as well as neural tube defects.
What does the result mean?
The result provides an estimate of the risk of chromosomal abnormalities or neural tube defects in the foetus. A "screen-positive" result indicates an increased risk, while a "screen-negative" result suggests a lower risk.
Why do the analysis?
The analysis is performed to identify pregnancies at higher risk for chromosomal abnormalities or neural tube defects, allowing for further diagnostic testing or counselling to be offered to expectant parents.
When to do the analysis?
Second trimester screening is typically performed between 15 and 22 weeks of gestation, with optimal timing around 16 to 18 weeks.
What sample is required?
A maternal blood sample is required for measuring serum markers, and an ultrasound scan is performed to assess foetal anatomy and nuchal translucency.
Is any type of prior preparation necessary?
No specific prior preparation is necessary for second trimester screening. However, it is advisable to discuss the screening procedure and its implications with a doctor beforehand.
How is it used?
The results of second trimester screening help guide further management decisions, such as whether to pursue invasive diagnostic testing (e.g., amniocentesis or chorionic villus sampling) for definitive diagnosis, or to provide additional support and resources for families facing potential chromosomal abnormalities or neural tube defects.
What are the normal values?
Normal values vary depending on the specific markers being measured and the ultrasound findings. Generally, a low-risk result indicates a probability below a specified threshold for the conditions being screened.
What does it mean to have altered values?
Altered values, or a "screen-positive" result, suggest an increased likelihood of chromosomal abnormalities or neural tube defects. Further diagnostic testing is typically recommended to confirm or rule out these conditions and provide accurate information for decision-making regarding pregnancy management.
Table of Values:
Result
Interpretation
Screen-Positive
Increased risk of chromosomal abnormalities or neural tube defects
Screen-Negative
Lower risk of chromosomal abnormalities or neural tube defects