Second Trimester Pregnancy Tests: When and How They Work

Quick take: The second trimester is when most routine prenatal screenings happen—from anatomy ultrasounds and the Quad screen to glucose tolerance and non‑stress tests. They’re designed to check your baby’s growth, detect common complications, and give you and your provider a clearer picture of the pregnancy. Most tests are safe, covered by insurance, and can be prepared for with simple steps like fasting or a full‑bladder scan.

It’s 10 p.m., you’re curled up on the couch, and a buzzing notification reminds you of your upcoming “second‑trimester labs.” Your mind races: “Will this be painful? What will they find? Do I need to change anything?” You’re not alone—millions of expectant parents feel the same mix of curiosity and anxiety as the pregnancy moves beyond the first three months.

In the second trimester (weeks 13–27), the focus shifts from confirming a pregnancy to monitoring the developing fetus and spotting any emerging health concerns. The tests you’ll encounter are mostly screening tools—ways to flag potential issues early—rather than definitive diagnoses. Understanding why each test matters, how to prepare, what the results mean, and what comes next can turn uncertainty into confidence.

Below you’ll find a complete guide to every common second‑trimester pregnancy test, why it’s recommended, how to get ready, what the numbers indicate, and what you can expect next. We’ve woven in real‑world experiences, practical tips, and the latest guidance from leading health authorities such as ACOG, the NHS, and the CDC.

What tests are done during the second trimester of pregnancy?

During weeks 13 to 27, most providers schedule a core set of screenings and diagnostic tests. The exact lineup can vary by country, insurance plan, and individual risk factors, but the most frequently ordered tests include:

• Anatomy ultrasound (mid‑pregnancy scan) – a detailed look at the baby’s organs, growth, and position.
• Quad screen (or quadruple serum test) – measures four hormones to assess the risk of certain chromosomal conditions and neural‑tube defects.
• Glucose tolerance test (GTT) – screens for gestational diabetes.
• Non‑stress test (NST) – evaluates fetal heart rate response to movements.
• Maternal blood pressure monitoring – checks for early signs of preeclampsia.
• Amniotic fluid assessment – often done via ultrasound to detect oligohydramnios or polyhydramnios.
• Placenta location check – ensures the placenta isn’t covering the cervical opening (placenta previa).

These tests collectively cover fetal anatomy, growth patterns, metabolic health, and maternal well‑being. They are recommended by the American College of Obstetricians and Gynecologists (ACOG) as part of standard prenatal care, and most public health systems (e.g., NHS England) include them in routine schedules.

Many families describe the second‑trimester visit as a “checkpoint.” One couple we spoke with shared that after the anatomy scan, they felt a surge of relief seeing their baby’s tiny hands and feet, even though the lab results later that week felt more intimidating. Knowing what each test looks for helps keep the focus on the big picture—ensuring a healthy pregnancy and preparing for any needed follow‑up.

Second trimester pregnancy screening tests

Quad screen vs. triple screen

The triple screen measures AFP, hCG (human chorionic gonadotropin), and estriol. The quad screen adds inhibin‑A, improving detection of Down syndrome and neural‑tube defects. Below is a quick comparison:

Both screens are performed with a simple blood draw. Results are reported as a “risk ratio” (e.g., 1 in 250) and a “multiple‑of‑the‑median” (MoM) for each marker. Higher MoM values for AFP suggest neural‑tube defects, while elevated inhibin‑A and hCG point toward a higher risk of Down syndrome.

According to the CDC, women who receive a high‑risk result are offered a diagnostic test, such as chorionic villus sampling (CVS) or amniocentesis, to confirm the finding.

Screening for gestational diabetes

Gestational diabetes screening is typically done between 24 and 28 weeks with a two‑hour, 75‑gram oral glucose tolerance test (OGTT). The test measures blood glucose before drinking the solution and at 1‑ and 2‑hour intervals. The thresholds set by ACOG are:

• Fasting: ≥ 92 mg/dL (5.1 mmol/L)
• 1‑hour: ≥ 180 mg/dL (10.0 mmol/L)
• 2‑hour: ≥ 153 mg/dL (8.5 mmol/L)

If any one value exceeds the cutoff, the diagnosis of gestational diabetes is made. Early detection allows for diet changes, glucose monitoring, and, when needed, medication to protect both mother and baby.

Non‑stress test during second trimester

A non‑stress test (NST) measures the baby’s heart rate in response to its own movements. During the test, a small ultrasound probe is placed on the abdomen, and a fetal heart‑rate monitor records beats for about 20–40 minutes. A “reactive” result—two or more accelerations of at least 15 bpm lasting 15 seconds—indicates good oxygenation and neurologic function.

Although NSTs are most often used in the third trimester for high‑risk pregnancies, they can be ordered in the second trimester if there are concerns such as reduced fetal movement, maternal hypertension, or a history of intrauterine growth restriction (IUGR). The procedure is painless, non‑invasive, and does not expose the baby to radiation.

One mother, who had a history of preeclampsia in a prior pregnancy, recalled the NST as “a quick check‑in that gave me peace of mind.” She was told to stay relaxed, and the technician let her listen to the baby’s heartbeat through the monitor speaker—a small but reassuring moment.

Second trimester pregnancy glucose test

The glucose test mentioned earlier is often called the “glucose tolerance test” (GTT) or “gestational diabetes screen.” Preparation is straightforward:

1. Fast for at least 8 hours (water is allowed).
2. Arrive at the lab in the morning; if you’re on insulin, discuss with your provider.
3. Drink the sweetened solution within 5 minutes.
4. Stay seated while blood is drawn at the 0‑, 1‑, and 2‑hour marks.

Most women experience a brief sweet taste and a slight nausea, but the test itself is low‑risk. If results are abnormal, your provider may repeat the test, suggest lifestyle modifications, or start medication such as insulin or metformin, following ACOG guidelines.

What to expect during a second trimester ultrasound

The anatomy ultrasound, usually performed between 18 and 22 weeks, is the centerpiece of second‑trimester imaging. Here’s what typically happens:

• Preparation: You’ll be asked to drink about 300 ml of water an hour before the appointment to fill the uterus with fluid, which improves image quality.
• Duration: The scan lasts 20–30 minutes.
• What’s examined: The sonographer evaluates the brain, spine, heart, lungs, kidneys, limbs, stomach, and placenta. They also measure the biparietal diameter (BPD) and femur length to estimate fetal weight.
• Possible findings: Normal anatomy, minor variations (like a small ventricular septal defect that often resolves), or concerns that may prompt further testing.

Most parents describe the moment they see the baby’s profile on the screen as “the most emotional part of the pregnancy.” One reader told us that the technician’s gentle explanation—“That’s your baby’s little heart beating strongly”—helped ease the anxiety of waiting for the images.

Second trimester pregnancy test schedule

While exact timing can differ by health system, a typical U.S. schedule looks like this:

In the UK, the NHS recommends a “mid‑wife scan” at 18–20 weeks and a “growth scan” around 28 weeks, with blood tests for anemia and infections scheduled alongside them. Insurance plans in the U.S. typically cover these core tests, though co‑pays may apply. Always verify coverage before the appointment.

Second trimester pregnancy screening for Down syndrome

Down syndrome (trisomy 21) risk is assessed using a combination of maternal age, serum markers (from the Quad screen), and sometimes a “cell‑free DNA” (cfDNA) test. While cfDNA can be done as early as 10 weeks, many providers repeat a serum screen in the second trimester for added reassurance.

For a typical Quad screen, a high‑risk result is usually reported as a risk greater than 1 in 270 (the threshold varies by lab). If the risk exceeds this, a diagnostic amniocentesis (performed at 15–20 weeks) is offered. Amniocentesis carries a small miscarriage risk (about 0.1–0.3 %), but it provides a definitive karyotype.

Studies cited by the National Institutes of Health (NIH) show that combining a first‑trimester nuchal translucency measurement with a second‑trimester Quad screen improves detection rates to over 90 % while keeping false‑positive rates below 5 %.

What is the quad screen test in pregnancy?

The quad screen is a blood test that measures four substances:

1. Alpha‑fetoprotein (AFP) – high levels may indicate neural‑tube defects.
2. Human chorionic gonadotropin (hCG) – elevated levels can signal Down syndrome.
3. Unconjugated estriol (uE3) – low levels are associated with chromosomal abnormalities.
4. Inhibin‑A – increased levels raise the risk for Down syndrome and trisomy 18.

Blood is drawn between 15 and 22 weeks, and results are expressed as a risk ratio. A “normal” quad screen means the calculated risk is below the lab’s cutoff (often 1 in 270). A “high‑risk” result triggers a discussion about diagnostic testing options.

According to the World Health Organization (WHO), the quad screen remains a valuable, low‑cost option in settings where cfDNA testing is not yet widely available.

Second trimester pregnancy test for gestational diabetes

The glucose tolerance test discussed earlier is the primary screen for gestational diabetes. Women with a history of gestational diabetes, obesity (BMI ≥ 30), or a family history of type 2 diabetes may be offered an earlier screen at 16–20 weeks.

Second trimester prenatal testing for genetic disorders

Beyond Down syndrome, the quad screen can also flag risks for trisomy 18 and trisomy 13. If any of these markers are abnormal, a referral for amniocentesis or chorionic villus sampling (if earlier) is made. Some centers also offer targeted cfDNA panels that focus on a broader set of chromosomal conditions.

Second trimester pregnancy tests for fetal development

The anatomy ultrasound is the cornerstone for evaluating fetal development. It confirms organ formation, assesses limb length, and checks for structural anomalies such as spina bifida, diaphragmatic hernia, or cardiac defects. Growth measurements (e.g., head circumference, abdominal circumference) are compared to standardized growth curves to identify potential intrauterine growth restriction (IUGR).

Second trimester pregnancy test for preeclampsia

Preeclampsia screening involves regular blood pressure checks, urine protein testing, and, in some protocols, measuring placental growth factor (PlGF) levels. Low PlGF combined with high blood pressure can predict early‑onset preeclampsia. The American College of Obstetricians and Gynecologists recommends low‑dose aspirin (81 mg) for women at high risk, starting before 16 weeks, but the decision is often reinforced after early second‑trimester labs.

Second trimester pregnancy test for fetal growth restriction

Fetal growth restriction (FGR) is evaluated through serial ultrasounds measuring abdominal circumference (AC) and estimated fetal weight (EFW). If the EFW falls below the 10th percentile, further monitoring—including Doppler studies of the umbilical artery—may be advised.

Second trimester pregnancy test for placenta previa

Placenta previa is diagnosed via transabdominal ultrasound when the placenta lies within 2 cm of the cervical os. If identified, providers recommend pelvic rest (no intercourse or digital exams) and schedule a repeat scan in the third trimester to see if the placenta migrates upward as the uterus expands.

Second trimester pregnancy test for amniotic fluid levels

Amniotic fluid volume is assessed with the “single deepest pocket” measurement or the “amniotic fluid index” (AFI). Values below 5 cm indicate oligohydramnios, while values above 24 cm suggest polyhydramnios. Both conditions can signal maternal or fetal issues and often lead to closer surveillance.

Second trimester pregnancy test costs and insurance coverage

Cost varies widely by country and insurance plan. In the United States, the average out‑of‑pocket expense for a Quad screen is $150–$250, while a detailed anatomy ultrasound can range from $200 to $500. The glucose tolerance test is often covered fully by Medicare and most private insurers, though a co‑pay may apply.

In the United Kingdom, the NHS provides all standard second‑trimester tests at no direct cost to the patient. For those with private health insurance, most plans reimburse the full fee, but it’s wise to confirm any prior‑authorization requirements.

If you’re concerned about cost, talk to your provider’s billing office early. Many clinics offer sliding‑scale fees or can connect you with charitable programs that assist with prenatal testing expenses.

From our medical team: All the tests described here are routine parts of prenatal care and have been shown to improve outcomes by identifying issues early. If you ever feel uncertain about a recommendation, ask your provider why the test is suggested, what the results could mean, and how it might change your care plan. Your comfort and safety are the top priorities.

Myth vs. fact

Myth: Second‑trimester tests are optional and only for “high‑risk” pregnancies.

Fact: While some tests are targeted to specific risk factors, most screening (like the Quad screen and anatomy ultrasound) is recommended for every pregnancy because they can uncover hidden problems that affect any baby.

Myth: The glucose tolerance test will cause a miscarriage.

Fact: The test is a simple blood draw and a sweet beverage; it does not increase miscarriage risk. The real risk comes from underlying diabetes, which the test helps manage.

Myth: A “normal” quad screen guarantees a healthy baby.

Fact: A normal screen means the measured risk is low, but it does not rule out all possible conditions. Ongoing prenatal care and ultrasounds remain essential.

Key takeaways

• Second‑trimester tests focus on anatomy, growth, and metabolic health, and are standard for most pregnancies.
• Common screenings include the quad serum test, anatomy ultrasound, glucose tolerance test, and blood‑pressure monitoring.
• Preparation is usually simple—fasting for the glucose test, drinking water for the ultrasound, and bringing a list of current medications.
• Results are risk‑based; a high‑risk finding leads to diagnostic follow‑up, not immediate treatment.
• Most tests are covered by insurance or public health systems; check with your provider if costs are a concern.
• If you notice serious symptoms—severe abdominal pain, bleeding, sudden swelling, or decreased fetal movement—contact your care team right away.

Frequently asked questions

What are the most common tests during the second trimester?

The most common are the anatomy (mid‑pregnancy) ultrasound, the quad screen, the glucose tolerance test for gestational diabetes, and routine blood pressure checks for preeclampsia.

Why are prenatal tests important during the second trimester?

They provide a window into the baby’s development and catch complications like neural‑tube defects, growth restriction, or gestational diabetes early, allowing timely interventions that improve outcomes for both mother and baby.

Can I decline second trimester pregnancy tests?

You can refuse any test, but it’s important to discuss the potential consequences with your provider. Declining a screening may mean missing an early sign of a condition that could be managed more easily if caught sooner.

What do second trimester pregnancy tests check for?

They assess fetal anatomy, growth measurements, risk of chromosomal abnormalities (via the quad screen), maternal blood‑sugar control, blood pressure trends, placenta position, and amniotic fluid volume.

How often should I have prenatal tests during the second trimester?

Typically, you’ll have a major anatomy ultrasound at 18–22 weeks, a quad screen around 15–20 weeks, and a glucose tolerance test at 24–28 weeks. Additional blood‑pressure and urine checks are done at each prenatal visit, usually every 4 weeks.

What are the risks of second trimester pregnancy tests?

All listed tests are considered safe. Ultrasound uses non‑ionizing sound waves, blood draws carry minimal infection risk, and the glucose test is non‑invasive. The only small risk is a slightly increased chance of miscarriage with invasive diagnostic procedures like amniocentesis, which are only done after an abnormal screening result.

When to call your doctor

If you experience any of the following, seek medical attention promptly: severe abdominal pain, vaginal bleeding, sudden swelling of hands or face, headaches with visual changes, decreased fetal movement, or a fever over 100.5 °F (38 °C). This article provides general information and does not replace personalized medical advice; always consult your obstetric provider with specific concerns.

References

1. American College of Obstetricians and Gynecologists (ACOG). “Practice Bulletin No. 190: Gestational Diabetes Mellitus.” 2023.
2. National Institute for Health and Care Excellence (NICE). “Antenatal Care.” Updated 2022.
3. Centers for Disease Control and Prevention (CDC). “Maternal and Infant Health – Pregnancy Screening Tests.” 2023.
4. World Health Organization (WHO). “Recommendations for Prenatal Screening.” 2022.
5. Mayo Clinic. “Quadruple marker test.” Accessed July 2024.
6. National Health Service (NHS). “Ultrasound scan during pregnancy.” Updated 2023.
7. Society for Maternal-Fetal Medicine (SMFM). “Guidelines for Non‑Stress Testing.” 2021.
8. American Academy of Pediatrics (AAP). “Guidelines on Gestational Diabetes.” 2022.