Triple Marker-Second Trimester
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No Fasting Required
Details
Maternal serum screening performed during the second trimester (usually between 15–20 weeks of pregnancy).
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Triple Marker-Second Trimester Test Information Guide
- Why is it done?
- Screen for chromosomal abnormalities in the fetus, particularly Down syndrome (Trisomy 21) and Edwards syndrome (Trisomy 18)
- Detect neural tube defects such as spina bifida and anencephaly
- Assess risk of congenital heart defects and other fetal abnormalities
- Evaluate pregnancies with increased risk factors including advanced maternal age (≥35 years), family history of genetic disorders, or abnormal first trimester screening
- Performed during the second trimester, typically between 15-22 weeks of gestation, with optimal timing at 16-18 weeks
- Normal Range
- Alpha-Fetoprotein (AFP): Normal range typically 0.7-2.5 MoM (Multiples of the Median) at 16-18 weeks gestation; measured in ng/mL or IU/mL with specific values varying by laboratory and gestational age
- Human Chorionic Gonadotropin (hCG): Normal range approximately 0.5-2.5 MoM; measured in mIU/mL with values decreasing as pregnancy progresses
- Unconjugated Estriol (uE3): Normal range typically 0.7-1.3 MoM; measured in ng/mL or nmol/L with values that increase during pregnancy progression
- Results expressed as MoM (Multiples of the Median) standardizes values across different laboratories and gestational ages; values between 0.5-2.5 MoM are typically considered low risk or negative screen
- Combined risk assessment determined by calculating overall detection rate; typical cutoff for positive screen is risk ≥1 in 250 to 1 in 270 live births
- Interpretation
- Low Risk (Negative Screen): Individual risk for Down syndrome and Edwards syndrome is below the established threshold (typically <1 in 250), indicating low likelihood of chromosomal abnormality; reassuring result but does not completely exclude possibility of genetic disorders
- High Risk (Positive Screen): Individual risk for chromosomal abnormality is above the threshold, suggesting increased probability of Down syndrome, Edwards syndrome, or neural tube defects; requires further investigation and counseling
- Elevated AFP: >2.5 MoM suggests increased risk for neural tube defects (spina bifida, anencephaly), abdominal wall defects, or other fetal anomalies; may also indicate multiple gestations or incorrect dating
- Low AFP: <0.7 MoM may indicate increased risk for Down syndrome when combined with elevated hCG and low uE3 in the characteristic triple marker pattern
- Elevated hCG: >2.5 MoM associated with increased Down syndrome risk; can also indicate molar pregnancy or multiple gestations
- Low uE3: <0.7 MoM, particularly when combined with low AFP and elevated hCG, suggests increased risk for Down syndrome and Edwards syndrome
- Accuracy of Triple Marker screening: Detects approximately 60-65% of Down syndrome cases and 50-70% of Edwards syndrome cases; detection rate for neural tube defects is approximately 80-85%
- Factors affecting interpretation include: accurate gestational dating (critical as markers change significantly with gestational age), maternal weight, maternal age, race/ethnicity, diabetes status, and smoking status
- False positive rate is approximately 5% when using cutoff of 1 in 250; false negative rate is approximately 35-40% meaning some affected pregnancies will have normal results
- Associated Organs
- Primary Organ Systems: Fetal brain and central nervous system, chromosomal and genetic systems of developing fetus, placental tissue (source of hCG)
- Down Syndrome (Trisomy 21): Chromosomal disorder affecting intellectual development, cardiac function, gastrointestinal system, and skeletal development; triple marker shows low AFP, elevated hCG, low uE3
- Edwards Syndrome (Trisomy 18): Severe chromosomal disorder with multiple organ involvement including congenital heart defects, renal abnormalities, and developmental delays; triple marker shows low AFP, low hCG, low uE3
- Patau Syndrome (Trisomy 13): Another severe chromosomal disorder; triple marker less sensitive for detection but may show abnormal marker combinations
- Neural Tube Defects: Including spina bifida and anencephaly affecting central nervous system development; elevated AFP is primary indicator
- Congenital Heart Defects: Structural abnormalities of the heart may be detected through abnormal marker combinations, particularly in Down syndrome
- Abdominal Wall Defects: Including gastroschisis and omphalocele; associated with elevated AFP
- Abnormal results may lead to psychological stress, anxiety, and need for prenatal counseling and further diagnostic testing
- Follow-up Tests
- Amniocentesis: Definitive diagnostic test recommended for positive triple marker screening; involves sampling amniotic fluid to analyze fetal cells for chromosomal abnormalities; typically performed after 15 weeks gestation
- Ultrasound Examination: Detailed fetal anatomy ultrasound to visualize structural abnormalities, assess for 'soft markers' of chromosomal disorders (such as cardiac echogenic foci, choroid plexus cysts, short femur), and confirm gestational dating
- Chorionic Villus Sampling (CVS): Alternative diagnostic test if positive screening detected and earlier diagnosis desired (typically 10-13 weeks); samples placental tissue for chromosome analysis
- Cell-Free DNA Testing (Noninvasive Prenatal Testing - NIPT): Advanced screening test analyzing fetal DNA fragments in maternal blood; higher detection rate (>99% for Down syndrome) and lower false positive rate; can be performed from 10 weeks gestation onward
- Genetic Counseling: Recommended for all positive results to discuss implications, risks of diagnostic testing, and available options
- First Trimester Screening Correlation: If available, combined with second trimester markers provides integrated screening (sequential screening) improving detection rates to 85-90%
- Repeat AFP Measurement: May be repeated if initial test inconclusive or affected by technical issues; repeat testing can confirm findings
- Specialized Fetal Echocardiography: Detailed cardiac ultrasound if cardiac defects suspected or markers suggest increased cardiac risk
- Fasting Required?
- Fasting Required: No
- Fasting is not required for Triple Marker screening as the test measures hormone and protein levels in maternal serum that are not significantly affected by food intake
- Patient Preparation: Routine blood draw requires no special preparation; patient may eat and drink normally before test
- Critical Timing Requirement: ACCURATE GESTATIONAL DATING IS ESSENTIAL - Test must be performed between 15-22 weeks of pregnancy, with optimal window at 16-18 weeks; incorrect dating significantly impacts result interpretation
- Prior Documentation: Bring documentation of last menstrual period (LMP) or confirm gestational age via recent ultrasound; inform healthcare provider of accurate gestational age
- Medications: No specific medications need to be avoided; continue all routine prenatal medications as prescribed
- Important Clinical Factors to Communicate: Inform provider of maternal age, race/ethnicity, maternal weight, diabetes status, smoking history, and any previous abnormal screening results as these affect interpretation
- Sample Collection: Simple blood draw via venipuncture; standard serum sample collected in tube without special handling; results typically available within 3-7 days
How our test process works!
