Pregnancy comes with a surprising amount of testing, and the names blur together fast: NIPT, NT, GBS, the anatomy scan, the glucose test. Are they all mandatory? What is each one even looking for? And what happens if something comes back "abnormal"? It's easy to feel like you're being swept along a conveyor belt of appointments without quite knowing what's happening.
So here's the calm version. We'll walk through the common tests in roughly the order you'll meet them, what each one checks, and — crucially — which are routinely recommended versus which are genuinely your choice. There's no pressure here, and there's no wrong answer.
First, the two words that make everything clearer
Before the alphabet soup, one distinction does most of the heavy lifting: screening versus diagnostic.
- A screening test estimates a chance. It comes back as "higher risk" or "lower risk," never a definite yes or no. Screening tests are simple and safe — usually blood draws and ultrasounds.
- A diagnostic test gives a definite answer. Amniocentesis and chorionic villus sampling (CVS) can confirm or rule out a chromosomal condition, but they involve a small procedure and a small risk, so they're offered selectively — often after a higher-risk screening result.
As ACOG puts it, screening and diagnostic options should be offered to everyone, and the choice to accept or decline is yours. A higher-risk screen is an invitation to learn more, not a verdict.
Carrier screening (before or early in pregnancy)
What it checks: whether you (and often your partner) carry genes for inherited conditions like cystic fibrosis, spinal muscular atrophy, or sickle cell disease. Carriers are healthy themselves, but if both partners carry the same condition, there's a chance of passing it on.
It's a simple blood, saliva, or cheek-swab test. ACOG recommends offering carrier screening to everyone considering or already in pregnancy — and is refreshingly direct that "carrier screening is your choice... there is no right or wrong choice." Doing it before pregnancy gives you the most options; doing it during is also fine.
Dating ultrasound (often weeks 6–13)
What it checks: confirms the pregnancy, checks for a heartbeat, counts how many babies are in there, and — most importantly — pins down your due date. An early ultrasound is the most accurate way to date a pregnancy, which then sets the timing for every test that follows. ACOG notes ultrasound is a safe, routine part of prenatal care.
First-trimester screening and NIPT (weeks 10–13)
This is where genetic screening usually begins, and you generally have two main paths (sometimes combined):
- NIPT / cell-free DNA screening. A blood test that analyzes tiny fragments of placental DNA circulating in your blood to screen for common chromosomal conditions like Down syndrome (trisomy 21) and trisomies 18 and 13. MedlinePlus and ACOG describe it as the most sensitive and specific screening for these conditions — but, again, a screen, not a diagnosis. It can also reveal fetal sex if you want to know.
- The combined first-trimester screen. This pairs a blood test (measuring proteins like PAPP-A and hCG) with an ultrasound called the nuchal translucency (NT) scan, which measures the thickness of the fluid at the back of the baby's neck. Together they estimate the chance of certain chromosomal conditions.
Some clinics offer integrated screening, which combines first- and second-trimester results for greater accuracy, including a second-trimester blood test (the quad screen) that also screens for neural tube defects like spina bifida.
If any of these come back higher-risk, your provider will talk through next steps — which may include diagnostic testing (CVS or amniocentesis). The key word is offer: at every fork, you decide how far you want to go.
The anatomy scan (around 18–22 weeks)
What it checks: often the appointment people look forward to most. This detailed ultrasound, sometimes called the mid-pregnancy or level 2 scan, examines your baby's anatomy head to toe — brain, heart, spine, kidneys, limbs — and checks the placenta, amniotic fluid, and growth. Per MedlinePlus, it's a routine, recommended part of second-trimester care. If you want to learn the baby's sex, this is usually when it can be seen. It's reassuring for most families, and if it flags something, it gives your care team time to plan.
Glucose screening (around 24–28 weeks)
What it checks: gestational diabetes, a form of high blood sugar that develops in pregnancy and usually causes no symptoms — which is exactly why it's screened for routinely. You'll drink a sweet glucose solution and have your blood sugar checked after an hour. If that screen is elevated, a longer follow-up test confirms the diagnosis. ACOG recommends this screening for essentially everyone, because catching and managing it protects both you and your baby. We go deep on what a diagnosis means in gestational diabetes, explained.
Group B strep, or GBS (around 36–37 weeks)
What it checks: whether you carry group B streptococcus, a common bacterium that lives harmlessly in the body of about 1 in 4 people but can occasionally cause serious infection in a newborn during birth. It's a quick, painless swab of the vagina and rectum near the end of pregnancy. If you test positive, ACOG explains that you'll simply be offered antibiotics through an IV during labor, which dramatically lowers the risk to your baby. A positive result isn't an infection — it just means you carry the bacteria, and the plan is straightforward.
A few others you might encounter
Depending on your history, you may also see routine bloodwork at your first visit (blood type and Rh factor, anemia, immunity to rubella, hepatitis B, HIV, and other infections), a urine test at most visits, and additional growth scans or fetal monitoring later if there's a specific reason. These round out the standard picture described by MedlinePlus.
Saying yes, saying no, and asking questions
Here's the part worth keeping: routine doesn't mean mandatory, and optional doesn't mean unimportant. Some tests — the anatomy scan, glucose screening, GBS — are recommended for nearly everyone because they protect health in concrete ways. Others, especially genetic and carrier screening, are deeply personal. People decline them for all sorts of valid reasons, and people pursue every available test for equally valid reasons. Neither choice makes you a better or worse parent.
A few good questions to bring to any test: Is this a screen or a diagnostic test? What would a result change for us? What are the next steps if it's higher-risk? Knowing what you'd do with the information helps you decide whether you want it.
It also helps to jot down each result and date as you go — it's easy to lose track across a dozen appointments. Many parents keep a simple running log so they can see the whole picture and bring good questions to the next visit.
The bottom line
Prenatal testing can feel like a lot because it is a lot — but each test has a clear job, and you're allowed to understand it before you consent to it. Screens estimate chances; diagnostics confirm answers; and at nearly every step, the test is offered to you, not done to you. Lean on your provider, ask what a result would mean, and make the choices that feel right for your family. That's the whole job.
This article is educational and not medical advice. Always check with your obstetric provider.