Second Trimester Prenatal Tests

During your second trimester (weeks 13–27), prenatal tests help check on your baby’s health and growth. Some are routine, like blood tests for your blood type and iron levels. Others may be recommended based on your health history or risk factors. Certain tests, such as amniocentesis, may be considered if there’s concern about birth defects. Later in pregnancy, additional tests can help confirm your baby is developing well.

Your healthcare provider, and sometimes a genetic counselor, can tell you which tests are recommended for your pregnancy and help you make informed decisions.

Routine Tests

These tests are part of regular prenatal care and usually happen at checkups:

• Blood tests to check your blood type, iron levels and more
• Urine tests to check for infection or other issues
• Ultrasounds to see how your baby is growing 

Screening Tests: Checking for Risks 

Screening tests can show if your baby may be at risk for certain conditions — but they don’t give a definitive answer. If a test shows something unusual, your provider may suggest more tests.  

Quadruple Marker Test

This blood test looks at four substances in your blood to spot possible risks for Down syndrome and other conditions.

Results usually take 1–2 weeks. If anything looks unusual, you might be offered an ultrasound or a diagnostic test like amniocentesis to learn more.

Expanded Alpha-fetoprotein (AFP) Screening

This blood test is usually done between 15 and 20 weeks. It can show risks for:

• Chromosome conditions, such as Down syndrome
• Problems with the brain or spine (neural tube defects, like spina bifida) 

Who should get this test? 
California health authorities recommend all pregnant people be offered this test.

How accurate is it? 
It’s a screening test, not a diagnosis. That means the results aren't always right. Some may show a higher risk even when everything is fine (false positive). If this happens, your provider may suggest more tests, such as amniocentesis, to get a clearer answer. A genetic counselor can also help explain your options. 

Gestational Diabetes Screening

Between 24 and 28 weeks of pregnancy, most people are screened for gestational diabetes. If you're higher risk, you may be screened earlier in pregnancy. Most of the time, gestational diabetes can be managed with diet and exercise changes alone. Some patients need medication for this condition. Talk to your care team about treatment and options if you're diagnosed with gestational diabetes.

Ultrasound (Sonogram)

Ultrasound uses sound waves to make pictures of your baby. Most second-trimester ultrasounds, often called anatomy ultrasounds, are done between 18 and 22 weeks. They help show how your baby is growing.

Is it safe? 
Yes. Studies show there are no known health risks to you or your baby.

Do ultrasounds hurt? 
Ultrasounds don't usually hurt. If you have an intravaginal ultrasound, you may feel some discomfort or notice some pressure. Sometimes, if your baby's in difficult position to see, the sonographer may ask you to move or gently press on your abdomen to get a better view. If anything feels uncomfortable, let them know — they can adjust or try a different position to make you more comfortable. 

What can it show?

• How many babies you’re carrying
• Some congenital differences — such as your baby growing or developing differently than expected
• Where the placenta is
• Your baby’s growth
• Your due date 

Special Ultrasounds 

Your provider may suggest more detailed ultrasounds if you have a higher risk for certain conditions. Keep in mind, though, that no scan can detect everything, and some conditions may not appear until later in pregnancy — or even until birth.

• Fetal echocardiogram: A close-up look at your baby’s heart that can detect most cases of serious heart problems. It’s if there's a family history of heart problems or if something unusual shows up on a routine scan.
• Targeted ultrasound: A close look at one body part or organ, often used if there’s a concern about a genetic or physical issue. 

What to Remember 

It's your choice whether to have a test or not. If you’re unsure or have questions, talk with your provider — they’re there to support you. If any test shows a possible abnormality, your care team may suggest you talk with a genetic counselor.