Complete Blood Count (CBC): What You Need to Know About This Common Blood Test
A blood test during pregnancy that measures three substances to assess the risk of certain birth defects and chromosomal conditions.
{"Screens for neural tube defects like spina bifida","Checks for chromosomal conditions such as Down syndrome","Performed between 15-20 weeks of pregnancy","Results indicate risk level, not a definitive diagnosis","A positive screen requires follow-up testing for confirmation"}
Key facts at a glance
- LOINC
- 35086-8
- Short code
- 2nd trimester 3 screen Pnl SerPl
- Synonyms
- 2nd trimester 3 screen Pnl SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What is this test? A complete blood count (CBC) is a routine blood test that measures the different cells in your blood, including red blood cells, white blood cells, and platelets, to evaluate your overall health.
The Second Trimester Triple Screen (also known as the maternal serum screen or triple test) is a blood test performed during the second trimester of pregnancy, typically between 15 and 20 weeks. It measures three specific substances in the mother's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and estriol (a form of estrogen produced by the placenta).
How is the test performed? A healthcare professional will draw a small sample of blood, usually from a vein in your arm, using a thin needle. The sample is then sent to a laboratory where it is analyzed under standard testing procedures.
A healthcare provider will draw a small blood sample from a vein in your arm. The sample is then sent to a laboratory for analysis. The test is simple and carries no risk to your pregnancy. Results are usually available within a few days to a week.
What do the results mean? Your results show whether your blood cell counts fall within normal ranges. Values that are too high or too low can point to infections, anemia, clotting problems, or other conditions that may require further evaluation by your provider.
The test measures the levels of the three substances and compares them to expected values based on your age, weight, race, and how far along you are in your pregnancy. Results are reported as screen-positive or screen-negative, indicating whether there is an increased risk for certain conditions.
What conditions does this test screen for? A CBC can help screen for anemia, infections, blood disorders such as leukemia, bleeding or clotting problems, and other conditions that affect the health of your blood and immune system.
The Triple Screen can help identify increased risk for: Neural tube defects (such as spina bifida or anencephaly), Down syndrome (trisomy 21), and other chromosomal abnormalities. It is important to understand that this is a screening test, not a diagnostic test. A positive result means there is a higher risk, not that the baby definitely has a problem.
What happens after the test? After the blood draw, you can return to your normal activities right away, and a small bandage will cover the puncture site. Your provider will review the results with you and discuss any follow-up testing or treatment that may be needed.
If your results show a higher risk, your healthcare provider may recommend additional diagnostic tests such as a detailed ultrasound or amniocentesis to confirm or rule out any conditions. A normal (negative) result reduces but does not eliminate the possibility of birth defects.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The Triple Screen is an important prenatal screening tool that helps identify pregnancies at increased risk for certain birth defects and genetic conditions. Early identification allows parents and healthcare providers to prepare for any special needs the baby may have. The test is typically offered to all pregnant women, though it may be particularly recommended for those with risk factors such as advanced maternal age (35 or older at delivery), previous child with a chromosomal condition, or family history of neural tube defects.
Frequently asked questions
Is the Triple Screen safe for my baby?
Will I need to fast before the test?
What if my test results are positive?
Can the Triple Screen predict all birth defects?
How accurate is the Triple Screen?
Should I get the Triple Screen or the Quad Screen?
Sources
- 1
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy