Maternal serum is a blood sample from a pregnant person, containing substances from the developing fetus and placenta. Analyzing maternal serum provides valuable information regarding the health of the pregnancy. It offers a non-invasive way to gain early insights into potential concerns without directly affecting the fetus.
The Role of Maternal Serum Screening
Maternal serum analysis screens for the chance of the developing fetus having certain chromosomal abnormalities or neural tube defects. These non-invasive screenings involve a routine blood draw, usually performed in the second trimester (15-22 weeks).
Commonly known as “triple screen” or “quad screen,” these tests are part of prenatal care. The triple screen measures three specific markers, while the quad screen includes a fourth marker, offering a higher likelihood of identifying at-risk pregnancies. These screenings help identify pregnancies that may benefit from further evaluation.
Key Substances Analyzed
Maternal serum screening measures specific biochemical markers to assess potential risks. Alpha-fetoprotein (AFP) is a protein produced by the fetal liver and yolk sac. Elevated AFP levels can suggest neural tube defects, such as spina bifida or anencephaly, or abdominal wall defects. Conversely, lower AFP levels may indicate an increased chance of certain chromosomal abnormalities.
Human chorionic gonadotropin (hCG) is a hormone produced by the placenta. High levels of hCG are often associated with an increased chance of Down syndrome, while low levels can suggest other chromosomal abnormalities like Trisomy 18. Unconjugated estriol (uE3), a form of estrogen, is produced by the fetus and placenta. Low levels of uE3 can be linked to Down syndrome or Trisomy 18.
Inhibin A is a placental hormone. Its inclusion in the quad screen enhances the detection rate for Down syndrome. Typically, elevated Inhibin A levels are observed in pregnancies affected by Down syndrome. The combined assessment of these markers, alongside factors like maternal age, gestational age, weight, and ethnicity, helps determine a numerical risk assessment.
Interpreting Screening Results
Maternal serum screening provides a risk assessment, not a definitive diagnosis. A “high risk” or “screen positive” result indicates an increased chance of a condition, but does not confirm its presence. Many individuals with a high-risk screening result proceed to have healthy babies. Similarly, a “low risk” or “screen negative” result does not guarantee the absence of a condition, as screening tests can have false negative results.
Screening tests are designed to identify individuals who might need further evaluation, differing from diagnostic tests that provide a conclusive “yes” or “no” answer. The accuracy of these screenings can be influenced by factors such as incorrect pregnancy dating or multiple pregnancies. Discussing results with a healthcare provider or genetic counselor is important for personalized interpretation and understanding implications.
What Happens After Screening
If maternal serum screening indicates a higher chance of a condition, several follow-up steps are available. Genetic counseling is often recommended to help individuals understand the screening results, discuss potential implications, and explore further testing options. This provides an opportunity to make informed decisions about pregnancy care.
Further diagnostic tests may be offered to confirm or rule out a suspected condition. Amniocentesis involves taking a small sample of amniotic fluid, which contains fetal cells, usually between 15 and 20 weeks. Chorionic villus sampling (CVS) involves collecting a tissue sample from the placenta, typically performed earlier in pregnancy, between 10 and 13 weeks. Both amniocentesis and CVS are diagnostic procedures that can detect chromosomal abnormalities with high accuracy.
Non-invasive prenatal testing (NIPT), also known as cell-free DNA screening, is another screening option for follow-up or as an alternative. NIPT analyzes fetal DNA fragments in the mother’s blood to screen for certain chromosomal conditions. Decisions regarding further testing are personal and are best made in consultation with medical professionals, considering individual circumstances and preferences.