What Is Prenatal Screening and When Should You Have It During Pregnancy?
Updated: Aug 24
Pregnancy comes with many routine appointments, scans and tests, and it is natural to wonder which ones are actually necessary. One important part of pregnancy care is prenatal screening, which helps estimate whether a baby has a higher chance of certain chromosomal, genetic or structural conditions.
So, what is prenatal screening, when should you have it, and what happens if a result shows an increased chance?
Prenatal screening uses ultrasound, blood tests or a combination of both to assess the likelihood of certain conditions during pregnancy. It does not usually confirm a diagnosis. Understanding this difference is important when deciding which screening options are right for you.
What Is Prenatal Screening?
Prenatal screening refers to tests performed during pregnancy to estimate the chance that a developing baby may have certain genetic, chromosomal or structural conditions.
Depending on the stage of pregnancy, screening may include:
First-trimester ultrasound
Nuchal translucency (NT) scan
Maternal blood tests
Combined first-trimester screening
Non-invasive prenatal testing (NIPT)
Detailed ultrasound or anomaly scan
The appropriate screening approach depends on your gestational age, medical history, pregnancy history and the options available to you.
ACOG recommends that prenatal genetic screening and diagnostic testing options be discussed and offered to pregnant patients, regardless of age or baseline risk.
When Should Prenatal Screening Be Done?
Prenatal screening is offered at different stages of pregnancy, and each test has its own recommended time window.
First Trimester: Early Pregnancy Screening
The first trimester is an important period for pregnancy assessment.
An early ultrasound may help confirm pregnancy location, establish gestational age and assess early fetal development.
During the appropriate gestational window, an NT scan may be performed as part of first-trimester screening.
The NT scan measures the fluid collection at the back of the fetal neck. This measurement may be combined with maternal blood test results and other factors to estimate the chance of certain chromosomal conditions.
NIPT: When Is It Done?
NIPT (Non-Invasive Prenatal Testing), also called cell-free DNA screening, analyses small fragments of placental DNA present in the mother's blood.
It can screen for certain chromosomal conditions, including trisomy 21, trisomy 18 and trisomy 13.
NIPT is generally available from around 10 weeks of pregnancy, although the exact timing and test options can vary.
The important point is that NIPT remains a screening test, not a diagnostic test. A high-risk result generally requires appropriate counselling and consideration of diagnostic testing.
ACOG states that cell-free DNA screening is the most sensitive screening test for common fetal aneuploidies, but it is not equivalent to diagnostic testing.
Second Trimester: Anomaly Scan
Another important part of prenatal assessment is the detailed anomaly scan, usually performed around the middle of pregnancy.
This ultrasound examines the baby's physical development and anatomy.
The specialist may assess:
Brain
Face
Spine
Heart
Chest
Abdomen
Kidneys
Bladder
Limbs
Placenta
Amniotic fluid
The NHS recommends a mid-pregnancy ultrasound examination to check the baby's physical development and screen for certain structural conditions.
The anomaly scan is important because chromosomal screening and ultrasound assess different aspects of pregnancy health.
Is Prenatal Screening Necessary for Every Pregnancy?
Screening options should be discussed individually with your healthcare provider.
Many pregnant women are offered screening, but you may not need every available test.
Your doctor may consider:
Your gestational age
Previous pregnancy history
Family history
Medical conditions
Previous screening results
Ultrasound findings
Your preferences
The goal is to choose appropriate screening rather than simply undergoing every test available.
What Does a High-Risk Screening Result Mean?
A high-risk or positive screening result does not mean that your baby definitely has the condition being screened for.
This is one of the most important points for parents to understand.
If screening indicates an increased chance, your doctor may recommend:
Reviewing the screening result.
Performing or reviewing a detailed ultrasound.
Providing genetic or fetal counselling.
Discussing further screening options.
Considering diagnostic testing such as CVS or amniocentesis.
The appropriate next step depends on the specific test result and the overall clinical picture.
What Is the Difference Between Screening and Diagnostic Testing?
The distinction is simple:
Screening: Estimates the likelihood of a condition.
Diagnostic testing: Provides diagnostic information about whether a specific condition is present.
Examples of screening include NIPT and first-trimester combined screening.
Examples of diagnostic testing include CVS and amniocentesis.
Because diagnostic procedures are invasive, they are generally considered after appropriate counselling and when there is a clinical reason to obtain more definitive information.
Can a Low-Risk Screening Result Guarantee a Healthy Baby?
No.
A low-risk screening result is reassuring, but it cannot guarantee that a baby has no genetic, structural or developmental condition.
Each screening test looks for specific conditions, and no prenatal screening test can detect every possible health problem.
This is why routine antenatal care and recommended ultrasound examinations remain important even after a low-risk screening result.
What Happens After Prenatal Screening?
The next step depends on your result.
If the result is low risk:
You will generally continue routine pregnancy care and recommended scans.
If the result shows increased risk:
Your doctor may recommend specialist counselling, additional ultrasound assessment or diagnostic testing.
The result should always be interpreted in the context of the entire pregnancy rather than considered in isolation.
How Can a Fetal Medicine Specialist Help?
A fetal medicine specialist can help you understand which screening options are appropriate and explain what each test can and cannot tell you.
Specialist counselling may be particularly helpful when:
Screening results are high risk
Ultrasound findings are unexpected
There is a family history of genetic conditions
Diagnostic testing is being considered
Parents are unsure which screening option to choose
The goal is to provide accurate information without creating unnecessary anxiety.
Conclusion
Prenatal screening is an important part of modern pregnancy care because it can help identify pregnancies that may need further assessment.
The timing and type of screening depend on your individual pregnancy. First-trimester screening, NT assessment, NIPT and the second-trimester anomaly scan each provide different information.
Most importantly, remember that a screening result is not a diagnosis. If a screening test shows an increased chance of a condition, your doctor or fetal medicine specialist can explain what the result means and discuss appropriate next steps.
Doctor’s Note
“Prenatal screening can provide valuable information during pregnancy, but parents should understand the difference between screening and diagnosis. A high-risk result does not automatically mean that the baby has a genetic or chromosomal condition. When a result is concerning, we consider the screening result alongside ultrasound findings, pregnancy history and other relevant factors before discussing further testing. Good counselling helps parents understand their options and make informed decisions without unnecessary fear.”
— Dr. Divya Ravikumar, MBBS, DNB (OG), MRCOG, PDF (Fetal Medicine), Fetal Medicine Specialist
FAQs
1. What is prenatal screening?
Prenatal screening consists of tests performed during pregnancy to estimate the likelihood of certain genetic, chromosomal or structural conditions. It may include ultrasound, maternal blood tests or cell-free DNA testing such as NIPT.
2. When should prenatal screening start?
Screening can begin during the first trimester. Different tests have different time windows, so your obstetrician or fetal medicine specialist can recommend when each screening examination should be performed.
3. Is NIPT a diagnostic test?
No. NIPT is a screening test that analyses cell-free DNA in the mother's blood to estimate the likelihood of certain chromosomal conditions. A high-risk result may require further evaluation or diagnostic testing.
4. What should I do if prenatal screening shows a high risk?
Do not assume that a high-risk result means your baby definitely has a condition. Speak with your doctor or fetal medicine specialist. They may recommend detailed ultrasound, counselling or diagnostic testing depending on the result and your pregnancy.
5. Can prenatal screening detect every problem?
No. Screening tests focus on specific conditions and cannot detect every genetic, structural or developmental problem. Routine antenatal care and recommended ultrasound examinations remain important throughout pregnancy.
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