First Trimester Screening Tests | Know Your Options Early

Hearing “first trimester screening” can feel like a lot, fast. You may be excited, tired, queasy, and suddenly staring at a list of tests with unfamiliar names. This page breaks down what those tests are, what they can and can’t tell you, when they’re done, and how people often use the results.

These tests don’t diagnose a condition. They sort pregnancies into “lower chance” and “higher chance” groups for certain findings. If a screen points to a higher chance, there are clear next steps. If a screen points to a lower chance, you still keep routine care and the mid-pregnancy anatomy scan.

What first trimester screening is built to do

Most first-trimester screening is about one thing: estimating the chance of chromosomal conditions like trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). Some options also screen for sex chromosome conditions, based on the test chosen.

At the same time, first-trimester visits often include checks that answer everyday questions that matter in real life: How far along am I? Is the pregnancy in the uterus? Is there one fetus or more? Is there a heartbeat? Those pieces may come from an ultrasound done for dating or symptoms, not only from a “screening” visit.

There isn’t one universal package. Clinics offer different paths based on local programs, your medical history, and what testing is available. The main options still fall into a few buckets, and once you see them side by side, the list stops feeling random.

First Trimester Screening Tests and what they measure

First Trimester Screening Tests usually refer to a combination of ultrasound markers and blood markers done in a tight window. The classic “combined” screen pairs a nuchal translucency (NT) ultrasound measurement with a blood test that measures pregnancy-associated plasma protein-A (PAPP-A) and free beta-hCG. Timing matters because these markers shift week by week.

Another option, cell-free DNA screening (cfDNA), uses a maternal blood sample to screen for common chromosomal conditions. Many labs offer it from around 10 weeks, and professional groups describe availability as early as 9–10 weeks in some settings.

Some people do one route. Others combine steps in a planned order, like a dating ultrasound first, then blood work, then a targeted NT scan. The order is usually about timing, scheduling, and what your clinic recommends for clean results.

Dating ultrasound and early scan checks

An early ultrasound can confirm gestational age, number of fetuses, and basic early development. Even when you plan cfDNA, an ultrasound around this time can still be useful because it checks that the pregnancy dating matches the testing window and can spot factors that change how results are interpreted.

Nuchal translucency (NT) ultrasound

The NT scan measures a thin fluid space at the back of the fetal neck during a narrow gestational window. The measurement is combined with gestational age and other factors to estimate chance of certain chromosomal conditions. The scan needs a trained sonographer and the right fetal position, so some appointments take longer than a standard look-see scan.

First-trimester blood markers (PAPP-A and free beta-hCG)

This blood draw measures substances linked with placental function. When paired with NT, age, and gestational dating, it forms the combined screen in many programs. Blood timing varies by clinic, but the goal is to keep it within the first-trimester screening window so the math behind the risk estimate stays valid.

Cell-free DNA screening (cfDNA)

cfDNA uses fragments of placental DNA in maternal blood to screen for common trisomies. It’s still a screening test, not a diagnosis, but it tends to be more accurate than older serum-only screens for trisomy 21. Many groups describe it as an option from around 10 weeks, with some sources noting 9–10 weeks availability.

Timing that keeps the results meaningful

Timing is the quiet force behind first-trimester screening. If the blood draw is too early or the NT scan is done outside the valid window, you can end up with a result that’s harder to trust or can’t be calculated at all. That’s why clinics schedule these visits in a fairly narrow band.

In many programs, the NT scan is done around 11 to 14 weeks, and the blood draw is done during a similar span. cfDNA is often offered from around 10 weeks onward. Local programs can differ, so your appointment letter may look a bit different from what a friend had in another city or country.

One practical tip: if your dates are uncertain, a dating scan first can prevent wasted testing. A difference of even a few days can shift what’s valid for a combined screen.

Test or step	Usual window	What it helps with
Dating ultrasound	Early first trimester	Gestational age, location of pregnancy, number of fetuses
Viability check (heartbeat, early growth)	Early first trimester	Confirms ongoing pregnancy and aligns timing for later screening
Nuchal translucency (NT) ultrasound	Often 11–14 weeks	Risk estimate for certain chromosomal conditions when paired with other inputs
PAPP-A blood marker	First-trimester window	Part of combined screening calculation with NT and gestational age
Free beta-hCG blood marker	First-trimester window	Part of combined screening calculation with NT and gestational age
Combined screening (NT + blood markers)	First-trimester window	Single risk estimate for trisomy 21, 18, 13 in many programs
Cell-free DNA screening (cfDNA)	Often from 10 weeks	Screening for common trisomies using maternal blood
Chorionic villus sampling (CVS) (diagnostic)	Often 10–13 weeks	Diagnostic chromosome testing using placental tissue sample

How to pick a screening path without getting lost

Most people start with a simple question: “What do I want this test to do for me?” Some want the earliest possible screening estimate. Some want fewer steps. Some want the lowest false-positive rate they can get from a screening test. Some want testing that fits with their values and what they would do with the information.

Here’s a clean way to think about the common paths:

• Combined screening path: NT ultrasound plus PAPP-A and free beta-hCG, with a single calculated chance estimate.
• cfDNA path: Maternal blood test from around 10 weeks, often paired with an ultrasound for dating and basic checks.
• Stepwise path: Start with one screen, then move to another test only if the first screen shows a higher chance.

If you’re in the UK or a program modeled on UK screening, you may see the “combined test” described as the routine first option for trisomy screening, with a different blood test offered later in pregnancy if the first-trimester window is missed.

If you’re in the US, professional guidance describes offering screening and diagnostic options to all pregnant patients, and clinics may present cfDNA alongside first-trimester combined screening as options. An updated ACOG practice advisory on screening for fetal chromosomal abnormalities lays out these options and how ultrasound markers and serum markers fit into screening.

What “screen positive” and “screen negative” actually mean

A screening result is a probability statement, not a diagnosis. A “screen positive” result means the calculated chance is above a program cutoff. It does not mean the fetus has the condition. A “screen negative” result means the chance is below the cutoff. It does not mean zero chance.

This is where plain language helps: screening sorts people into groups so that diagnostic testing can be offered to the smaller group that needs clearer answers.

What can shift accuracy

Several factors can change how screening performs, and none of them are a moral failing. They’re math and biology. Gestational age matters. Ultrasound quality matters. In cfDNA, factors like low fetal fraction can lead to a “no call” result and a need for redraw or another testing route. Some twin pregnancies also change what tests are available or how results are reported.

If you want the technical details on cfDNA availability and performance notes, the SMFM Consult Series on cell-free DNA screening summarizes current guidance and timing.

When diagnostic testing enters the picture

Diagnostic tests answer a different question than screening tests. They look directly at fetal or placental cells to determine whether a chromosomal condition is present. They’re offered for many reasons, including a screen showing a higher chance, an ultrasound finding, or a known genetic concern in the family.

CVS in the first trimester

Chorionic villus sampling (CVS) is typically done in the first trimester. A clinician takes a small sample of placental tissue, then the lab tests it. Because it’s diagnostic, it can confirm or rule out certain chromosomal conditions rather than estimating probability. The CDC overview on chorionic villus sampling and amniocentesis describes how CVS allows earlier diagnostic information compared with amniocentesis.

Amniocentesis later in pregnancy

Amniocentesis is generally done later than CVS. It samples amniotic fluid and can provide diagnostic answers about chromosomal conditions. Some families prefer to wait for this timing, especially if they’re also seeking testing that relates to open fetal defects, which are commonly screened in the second trimester.

Both CVS and amniocentesis carry procedure risks that your clinic should explain in plain terms with local numbers. Those risks differ by operator experience and setting. When you’re weighing options, ask for the clinic’s own complication rates, not only a generic statistic copied from somewhere else.

Result pattern	What it tends to mean	Common next step
Screen shows lower chance	Risk estimate falls below cutoff	Continue routine prenatal care and plan anatomy scan
Screen shows higher chance	Risk estimate exceeds cutoff	Offer diagnostic testing options and targeted ultrasound
cfDNA “no call” or low fetal fraction	Lab can’t report a result	Redraw, ultrasound review, or choose another test route
NT measurement higher than expected	Raises chance for chromosomal or structural findings	Referral for detailed scan and discussion of diagnostic testing
Dating scan changes gestational age	Original window may shift	Reschedule blood draw or NT to match valid timing
Twin pregnancy discovered	Some screens report differently	Use a twin-appropriate screening approach guided by clinic protocol

What to bring to your appointment and what to ask

People often show up thinking the test is “just bloodwork,” then realize the appointment is also about timing, ultrasound images, and decisions. A little prep keeps things calm.

Bring these details

• Your best estimate of last menstrual period, plus any cycle irregularity notes
• Any prior ultrasound dates and reports, if you’ve had one
• Family history of chromosomal or genetic conditions, if known
• Medication list and any chronic conditions on your chart

Ask these questions in plain language

• “Which screening tests does this clinic offer in the first trimester?”
• “What week is best for the NT scan here?”
• “If my screen shows a higher chance, what happens next at this clinic?”
• “If cfDNA comes back with no result, what’s your usual plan?”
• “Do you offer CVS here, or do you refer out?”

It also helps to ask how results are delivered. Some clinics call for higher-chance results and post lower-chance results in a portal. Knowing the pattern keeps you from refreshing your phone all day.

How results can affect the rest of prenatal care

First-trimester screening rarely lives in isolation. It can change the pace and type of follow-up imaging, and it can shape what testing comes next. A higher-chance result might lead to a detailed ultrasound earlier than planned, plus a referral for diagnostic testing if you want a yes-or-no answer.

A lower-chance result may let you breathe easier, but it doesn’t replace the anatomy scan later in pregnancy. Screening is aimed at specific conditions, and pregnancy care still includes checks for fetal anatomy, placental location, and growth over time.

If you want a clear description of how the combined test is used in a national screening program, the NHS page on screening for Down’s, Edwards’ and Patau’s syndromes explains timing and what the offered screens cover.

Common mix-ups that cause stress

Mix-up: Screening and diagnosis are the same

They’re not. Screening gives a chance estimate. Diagnostic testing can confirm or rule out specific chromosomal conditions.

Mix-up: A higher-chance screen means the fetus has a condition

It doesn’t. A screen is designed to catch as many affected pregnancies as possible, which means some unaffected pregnancies will also screen positive.

Mix-up: A lower-chance screen means zero chance

It doesn’t. It means the calculated chance is below a cutoff. That’s still useful, since it guides whether diagnostic testing is offered, but it’s not a guarantee.

Taking the next step that fits your values

People choose testing for different reasons, and that’s normal. Some want as much early information as possible. Some want to avoid procedures unless there’s a strong reason. Some want to keep testing minimal and stick with routine scans. Your plan can be steady even if your feelings change week to week.

If you feel stuck, try this small exercise: decide what kind of result would change your next step. If nothing would change, a complex testing plan may not be worth the stress. If a higher-chance screen would change your plan, focus on the screening route that best lines up with your timeline and what your clinic offers.

Whatever you choose, the best outcomes come from clean timing, good ultrasound technique, and clear follow-up plans. That’s the part you can control.