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Prenatal Tests: Second Trimester

Lea este articulo en EspanolThroughout your pregnancy, you’ll want to know how your baby is growing. You’ll also want to know if how you’re feeling is normal. Prenatal tests can offer you valuable information about your health and the health of your growing child.

If your doctor recommends a screening or test, be sure to learn about the risks and benefits. Most parents agree that prenatal tests offer them peace of mind while helping to prepare them for their baby’s arrival. But it’s your choice to accept or decline a test.

Read on to learn about tests that may be available to you during your second trimester.

What's a Screening Test

Routine Screenings & Tests

Your first visit to the obstetrician (if you haven’t gone already) should include a pregnancy test to confirm the pregnancy and a full physical that includes a pelvic exam. Your urine (pee) also will be tested for protein, sugar, and signs of infection.

If you’re due for your routine cervical test (Pap smear), the doctor will perform it during the pelvic exam. This test detects changes in your cervical cells that could lead to cancer.

To do a Pap smear, the inside of your cervix (the opening to the uterus that’s located at the very top of the vagina) will be swabbed with a cotton swab. This may be a little uncomfortable, but it is over quickly. During the pelvic exam your doctor will likely also check for sexually transmitted diseases (STDs) like chlamydia and gonorrhea.

In addition, blood will be drawn to check for things like:

  • your blood type and Rh factor. If your blood is Rh negative and your partner’s is Rh positive, you may develop antibodies that prove dangerous to your fetus. This can be prevented through a course of injections given to you.
  • anemia, a low red blood cell count
  • hepatitis B, syphilis, and HIV
  • immunity to German measles (rubella) and chickenpox (varicella)
  • cystic fibrosis — health care providers now routinely offer this screening even when there’s no family history of the disorder

After the first visit, you can expect to get your urine tested and your weight and blood pressure checked at every (or almost every) visit until you deliver. The reason for this is to identify conditions such as gestational diabetes and preeclampsia.

Throughout your second trimester, you’ll be offered more tests depending on your age, health, family medical history, and other factors.

Multiple Marker Test

Why Is This Test Performed?

Between the 15th and 20th weeks of pregnancy, expectant mothers usually are offered a blood test called the multiple-marker test (also called the multiple marker screening, maternal serum screening, or maternal blood screening). Doctors use this test to screen for Down syndrome and neural tube defects.

Depending on the number of things measured, this screening also might be called:

  • a “triple screen” or “triple marker” because it looks at the levels of a protein, alpha-fetoprotein (AFP), and two pregnancy hormones, estriol and human chorionic gonadotropin (hCG)
  • a “quadruple screen” (“quad screen”) or “quadruple marker” (“quad marker”) when the level of an additional substance — inhibin-A — is also measured

This screening calculates a woman’s individual risk based on the levels of the three (or more) substances, as well as:

  • her age
  • her weight
  • her race
  • whether she has diabetes requiring insulin treatment
  • whether she is carrying one fetus or multiple ones

The greater number of markers increases the accuracy of the multiple marker test and better identifies the possibility of a problem. In some cases, doctors will combine the results of this test with results from the first trimester screen (a blood test and/or ultrasound done at around 13 weeks to check for chromosomal abnormalities) to get an even better idea of a baby’s risk for Down syndrome and neural tube defects.

Should I Have This Test?

All women are offered some form of this test. Some practitioners include more parts of it than others. Remember that this is a screening, not a definitive test — it indicates whether a woman is likely to be carrying an affected fetus. It’s also not foolproof — Down syndrome, another chromosomal abnormality, or a neural tube defect may go undetected, and some women with abnormal levels have been found to be carrying a healthy baby. Further testing is recommended to confirm a positive result.

When Should I Have This Test?

The blood tests are typically done between 15 and 20 weeks.

How Is the Test Performed?

Blood is drawn from the mother.

When Are the Results Available?

Usually within a week, although it may take up 2 weeks.


Why Is This Test Performed?

Ultrasounds were once used only in high-risk pregnancies but have become so common that they’re often part of routine prenatal care.

During an ultrasound, sound waves are bounced off the baby’s bones and tissues to construct an image showing the baby’s shape and position in the uterus. Also called a sonogram, sonograph, echogram, or ultrasonogram, ultrasounds are used to:

  • verify the expected date of delivery
  • detect pregnancies outside the uterus
  • see whether there might be more than one fetus
  • determine whether the fetus is growing at a normal rate
  • record fetal heartbeat or breathing movements
  • check the amount of amniotic fluid in the uterus
  • indicate the position of the placenta in late pregnancy (which can sometimes block the baby’s way out of the uterus)
  • guide doctors during other tests, like amniocentesis
  • find structural defects that may indicate Down syndrome, spina bifida, or anencephaly
  • detect other problems such as congenital heart defects, cleft lip or palate, and gastrointestinal or kidney malformations

Should I Have This Test?

This test is considered safe, but it’s up to you to decide whether to undergo it. Talk to your health care provider to find out why this test is recommended for you.

When Should I Have This Test?

Ask your doctor when you will need to have an ultrasound. Most second-trimester ultrasounds, or “level 2” ultrasounds, are usually given between 18 and 20 weeks to examine a baby’s anatomy and to confirm that the baby is developing normally.

It’s during this test that a baby’s gender usually can be determined (as long as the baby is “cooperating” and in the right position). If you want your baby’s gender to be a surprise, make sure to tell the doctor or technician at the start of your test.

Women with high-risk pregnancies may need to have multiple ultrasounds throughout their second trimester.

When Are Results Available?

Although the technician can see the images immediately, a full evaluation by a doctor may take up to 1 week if one is not on site during the exam.

Depending on where you have the ultrasound done, the technician may be able to tell you that day whether everything looks OK. However, most radiology centers or health care providers prefer that technicians not comment until a specialist has taken a look — even when everything is OK.

Glucose Screening

Why Is This Test Performed?

Glucose screenings check for gestational diabetes, a short-term form of diabetes that develops in some women during pregnancy. Gestational diabetes is increasing in frequency in the United States, and may occur in 3% to 8% of pregnancies. Gestational diabetes can cause health problems for the baby, especially if it is not diagnosed or treated.

Should I Have This Test?

Most women have this test, and if they have gestational diabetes, are treated to reduce the risk to the baby.

When Should I Have This Test?

Screening for gestational diabetes usually is done at 24 to 28 weeks. Testing may be done earlier for women who are at higher risk of having it, such as those who:

  • have previously had a baby that weighed more than 9 pounds (4.1 kilograms)
  • have a family history of diabetes
  • are obese
  • are older than age 25
  • have sugar in the urine on routine testing
  • have high blood pressure (hypertension)
  • have polycystic ovary syndrome (POS)

How Is the Test Performed?

This test involves drinking a sugary liquid and then having your blood drawn after an hour. If the sugar level in the blood is high, you’ll have a glucose-tolerance test, which means you’ll drink a glucose solution on an empty stomach and have your blood drawn once every hour for 3 hours.

When Are the Results Available?

The results are usually available within 1 to 2 days. Ask if your health care provider will call you with the results if they are normal or only if the reading is high and you need to come in for another test.


Why Is This Test Performed?

This test takes a sample of the amniotic fluid that surrounds your baby, and examines the substances in the fluid, like genetic information. It is most often used to identify:

  • Down syndrome and other chromosome abnormalities
  • structural defects such as spina bifida and anencephaly
  • inherited metabolic disorders like PKU (phenylketonuria)

Doctors sometimes check for infection and Rh incompatibility with this test. Late in the pregnancy, this test can reveal if a baby’s lungs are strong enough to allow the baby to breathe normally after birth. This can help the health care provider make decisions about inducing labor or trying to prevent labor, depending on the situation. For instance, if a mother’s water breaks early, the health care provider may want to try to hold off on delivering the baby as long as possible to allow the baby’s lungs to mature.

Other common birth defects, such as heart disorders and cleft lip and palate, can’t be determined using this test.

Should I Have This Test?

Your health care provider may recommend this test if you:

  • had an abnormal screening test
  • are older than age 35
  • have a family history of genetic disorders (or a partner who does)
  • have had a previous child with a birth defect or had a previous pregnancy with a chromosomal abnormality or neural tube defect

This test can be very accurate — close to 100% — but only certain disorders can be detected. The rate of miscarriage with this procedure is between 1 in 300 and 1 in 500. It also carries a low risk of uterine infection, which can also cause miscarriage, leakage of amniotic fluid, and injury to the fetus.

Talk to your doctor to find out why this test is recommended for you, and to weigh the pros and cons of undergoing this test.

When Should I Have This Test?

Amniocentesis is usually performed between 15 and 20 weeks.

How Is the Test Performed?

While watching with an ultrasound, the doctor inserts a needle through the abdominal wall into the uterus to remove some (about 1 ounce) of the amniotic fluid. Some women report that they experience cramping when the needle enters the uterus or pressure while the doctor retrieves the sample.

The doctor may check the fetus’ heartbeat after the procedure to make sure it’s normal. Most doctors recommend rest for several hours afterward.

The cells in the withdrawn fluid are grown in a special culture and then analyzed (the specific tests conducted on the fluid depend on personal and family medical history).

When Are the Results Available?

Timing varies; depending on what is being tested for, the results are usually available within 1 to 2 weeks. Tests of lung maturity are often available within a few hours.

Percutaneous Umbilical Blood Sampling (PUBS)

Why Is This Test Performed?

This test obtains fetal blood by guiding a needle into the umbilical cord. It is primarily used in addition to an ultrasound and amniocentesis if your health care provider needs to quickly check your baby’s chromosomes for defects or disorders or is concerned that your baby may have another problem, such as a low platelet count or a thyroid condition. Alternative names for PUBS include cordocentesis, fetal blood sampling, or umbilical vein sampling.

The advantage to this test is its speed. In some situations (such as when a fetus shows signs of distress) it’s helpful to know whether the fetus has a fatal chromosomal defect. If the fetus is suspected to be anemic or to have a platelet disorder, this test is the only way to confirm it because it uses a blood sample rather than an amniotic fluid sample. It also allows transfusion of blood or needed fluids into the baby while the needle is in place.

Should I Have This Test?

This test may be used:

  • after an abnormality has been noted on an ultrasound
  • when results from other tests, such as amniocentesis or CVS, aren’t conclusive
  • if the fetus may have Rh incompatibility, to determine whether the baby has an infection if you’ve been exposed to an infectious disease

Risks are associated with this procedure, such as miscarriage or infection. The risks and benefits should be discussed with your health care provider if you choose to have this test.

When Should I Have This Test?

After 18 weeks.

How Is the Test Performed?

A fine needle is passed through your abdomen and uterus into the umbilical cord and blood is withdrawn for testing.

When Are the Results Available?

Usually within 3 days.

Additional Screenings for Couples at Risk

Throughout your pregnancy, your health care provider will order other tests based on, among other things, your (and your partner’s) personal medical history and risk factors. If your baby is at risk for certain hereditary conditions, you will be given an appointment to speak with a genetic counselor.

Screenings or diagnostic tests offered to those at risk for certain conditions include tests for:

Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: January 2014