Prenatal Tests in the 2nd Trimester

By now, you know the routine. The second trimester prenatal visits are more predictable. You look forward to that special moment when you can hear the baby's heartbeat for the first time. You've likely established a comfortable relationship with your doctor, too. Routine tests continue along with some specialized birth defect screenings and testing for gestational diabetes.

Routine Tests

At each doctor visit, you continue to have urine testing to check for protein, sugar, and any signs of infection. The doctor or nurse checks your weight and blood pressure as well. More exciting are the measurement of your growing abdomen and the first sounds of your baby's heart.

  • Fundal height. Starting at about 20 weeks, your doctor will measure the height of your uterus (fundal height). This helps verify the baby's gestational age and whether he or she is growing as expected. If the fundal height doesn't match up with the expected gestational age, you may need an ultrasound to find out why.
  • Fetal heart tones. By the beginning of your second trimester, your doctor can probably hear fetal heart tones using a handheld ultrasound device.


You will likely have an ultrasound between weeks 18 and 20. You may be able to watch the tiny heart beating! You might also get a peek at your baby's genital area to find out if it's a girl or boy – if you want to know.

At this stage, ultrasound confirms that you have one baby. It can also evaluate:

  • Baby's gestational age (and close in on your due date)
  • Normal growth and anatomy
  • Placement of the placenta
  • Amount of amniotic fluid
  • Baby's sex

Blood Sugar Test

Your doctor will test for gestational diabetes between weeks 24 and 28. If you are at high risk for developing gestational diabetes or if you have evidence of sugar in your urine, your doctor will likely do these tests earlier in your second trimester.

Optional Screening for Birth Defects

During your second trimester, your doctor will offer additional screening for birth defects, especially if you have a family history of birth defects or are over age 35. Your doctor will recommend what's best for you, depending upon your risk factors and results from any first trimester screening. You also should decide whether or not you want these tests. Some people decide that the results will not affect their plans for their pregnancies, so they do not want to go through testing that may cause them unnecessary stress. Note that doctors offer the multiple marker screen to all women, regardless of their age or risk.


Multiple marker screening. This test is offered to all women regardless of risk. A doctor takes a sample of your blood between the 15th and 20th weeks of pregnancy. You might hear these screenings referred to as triple screen, quadruple screen, or alpha fetoprotein (AFP) test. These tests can detect defects or levels of hormones that may indicate a possible problem.

NIPT screening- “Non-invasive prenatal testing- This test is generally offered to high risk patients. It is a blood test that looks at broken down fetal cells that are in the mother’s circulating blood to screen for Down’s Syndrome, Trisomy 18 and 13 and some sex chromosomal abnormalities. It can be done between 10-22 weeks of your pregnancy.

Amniocentesis. What if you are at increased risk or if the multiple marker screening or other factors indicate risk for a birth defect? You have the option of having an amniocentesis. This can diagnose chromosomal disorders or certain other defects. During an amniocentesis, the doctor guides a thin needle into the uterus to collect a sample of amniotic fluid for testing.

Now what? If your test results indicate risk for or an actual birth defect, you may want to consult with a genetic counselor. This person can help you understand the test results and risks and can help you understand your options.

WebMD Medical Reference Reviewed by Traci C. Johnson, MD on July 22, 2019



Lucile Packard Children's Hospital at Stanford: "Common Tests During Pregnancy."

U.S. Department of Health and Human Services Office on Women's Health: "Prenatal care and tests."

March of Dimes: "Routine prenatal tests."

American College of Nurse Midwives: "Second Trimester Tests."  

 American College of Obstetricians and Gynecologists: "Screening for Birth Defects," "Gestational Diabetes," and Your Pregnancy and Childbirth, Month to Month. 5th edition. 2010.

American Association for Clinical Chemistry. Lab Tests Online: "Second Trimester: Blood Glucose," "Second Trimester; Triple Marker or Quad Marker Screen," and "Amniotic Fluid Analysis."

Society of Obstetricians and Gynaecologists of Canada: "Content of a Complete Routine Second Trimester Obstetrical Ultrasound Examination and Report."

American College of Radiology: "ACR-ACOG-AUIM Practice Guideline for the Performance of Obstetrical Ultrasound." 

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