Prenatal Testing Basics

Ultrasound Screening for Anatomy

Black doctor giving pregnant patient ultrasound
Ariel Skelley/Blend Images/Getty Images

Screens for: fetal anatomy and problems with the baby or pregnancy. An example might be gastroschisis (abdominal wall opening), a placental issue like a placenta previa, spina bifida or other missing or defective anatomical problems with a baby.

Who does it: Ultrasounds should be done by trained and certified ultrasonographers or physicians.

How it is done: Ultrasounds are done by having mom drink enough water to fill her bladder, providing a better image for the screener. A gel is applied to help conduct the sound waves from the transducer placed on your abdomen. The sound waves are returned to the machine and an image is displayed on the screen for the practitioner to interpret.

When is it done: A fetal anatomy screen, sometimes called an anomaly screen, is usually best performed between 18-20 weeks of gestation. There are other times that work best for specific scans of a particular part of the baby's anatomy.

Accuracy: Depends on the age of gestation, what was found, the machine used and the person performing and reading the scan. Be sure to ask your doctor or midwife for specific if something is found or if you are concerned.

Risk to mom: It can be uncomfortable to have a full bladder and to lay back. Some mothers also report anxiety about the findings.

Risk to pregnancy/baby: None reported at this time.

Additional resources:

Urine Screen

Urine Dip Stick. Photo © RE Weiss

Screens for: variety of conditions including bacterial infections, sugar, protein, etc. These might indicate further issues like preeclampsia, gestational diabetes, urinary tract infections, etc.

Who does it: This is frequent performed at every prenatal visit with your midwife or doctor. It may be done by a lab tech, a nurse, your practitioner or even by the pregnant woman. It can be done at home or in the office as needed.

How it is done: Urine is collected in a cup or other collection device. Test strips are dipped in the urine and interpreted via a chart.

When is it done: Throughout pregnancy.

Accuracy: Varies depending on the type of screening and product used to test.

Risk to mom: She can miss the collection container and get her hands wet with urine. Does produce anxiety in some women.

Risk to pregnancy/baby: None known.

Maternal Blood Sampling

Screens for: Blood type for Rh incompatibility, certain diseases like Hepatitis, HIV status and blood counts that may indicate issues like anemia, gestational diabetes, infection, etc. It can also be done as a pregnancy test by looking for hCG in the blood.

Who does it: This is usually performed by a lab tech, nurse or other health care worker.

How it is done: It is done with a needle to puncture your vein to draw blood for the screening.

When is it done: It can be done at any point in pregnancy. It is typically done at the beginning of pregnancy and repeated as needed at various points in pregnancy such as a part of the Alpha-fetoprotein screening, gestational diabetes testing, etc.

Accuracy: Depends on the blood sample, and method of testing for which particular test.

Risk to mom: There is a slight pain during the testing. You may bleed a bit and have a bruise from the location where the blood is drawn. A very small percentage of women will have further trouble with the site like infection.

Risk to pregnancy/baby: None known.

Additional resources:

Chorionic Villus Sampling (CVS)

Screens for: Genetic/chromosomal disorders of the baby such as Trisomy 13, Trisomy 18 and Down syndrome.

Who does it: This is typically done by a maternal fetal medicine specialist (MFM) or an OB/GYN.

How it is done: A small needle/catheter is placed either through the abdomen or through the vagina near the uterus to collect a small sample of villi. Ultrasound is used to guide the needle/catheter away from the baby.

When is it done: It can be done as early as 10 weeks gestation, though many only offer this between weeks 10-12.

Accuracy: Nearly 100%, barring lab error

Risk to mom: Small risk of infection from the procedure. Procedure is uncomfortable. You may experience cramping or spotting after the procedure.

Risk to pregnancy/baby: Has a very small percentage of risks of birth defects. Most studies report a less than 1% miscarriage rate from the CVS procedure.

Additional resources:

Amniocentesis (Amnio)

Screens for: This test can be used to determine if your baby has a chromosomal disorder or for fetal lung maturity.

Who does it: This is typically done by a maternal fetal medicine specialist (MFM) or an OB/GYN.

How it is done: A small needle is placed through the abdomen into the uterus to collect a small sample of amniotic fluid. Ultrasound is used to guide the needle away from the baby and the placenta.

When is it done: Genetic disorders testing can be done as early as 16 weeks until the end of pregnancy. Fetal lung maturity is done before the decision is made to induce or let preterm labor continue, usually after 34 weeks.

Accuracy: Barring lab error, virtually 100%.

Risk to mom: The procedure may be uncomfortable to painful. Cramping and spotting may follow the test.

Risk to pregnancy/baby: The earlier the test is done the higher the rate of miscarriage. After the first trimester the miscarriage rate is between 1 in 200 and 1 in 400 procedures. There are also risks of amniotic fluid leakage.

Alpha-Fetoprotein (AFP) Screening

Pregnant Woman having blood work drawn
Photo © Photo Science Library/Getty Images

Screens for: Neural tube defects like spina bifida. Can potentially screen Down syndrome as well.

Who does it: Blood draw is done by a nurse or lab tech.

How it is done: A needle is placed into your vein and blood is drawn to take to the lab. There are up to four substances checked: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol and inhibin-A.

When is it done: Between 15-18 weeks for best results.

Accuracy: The more hormones used, the more accurate. It is important to point out that this test is a screening. If this test is positive it does not mean that your baby is suffering from one of these problems, just that further testing may be needed.

Risk to mom: Slight pain from needle stick, rare potential for infection at the site of the blood draw.

Risk to pregnancy/baby: None known.

Additional information:

Also known as the triple screen, quad screen or AFP.

Cordocentesis/Percutaneous Umbilical Cord Blood Sampling (PUBS)

Screens for: Cases of Rh sensitization when the fetus needs a blood transfusion.

Who does it:This is typically done by a maternal fetal medicine specialist (MFM) or an OB/GYN.

How it is done: With ultrasound guidance a small needle is placed into the uterus to obtain a sampling of blood from the umbilical cord.

When is it done: Not until after the 18th week of gestation.

Accuracy: Virtually 100%, barring lab error.

Risk to mom: Procedure can be uncomfortable, cramping may occur afterwards.

Risk to pregnancy/baby: There is about a 1-2% risk of miscarriage.

Stress/Non-Stress Testing

Mother with fetal monitor non-stress test
Photo © Moment/Getty Images

Screens for: Fetal activity and well-being late in pregnancy.

Who does it: Nurse, doctor or midwife.

How it is done: A non-stress test is done by electronic fetal monitoring (EFM), while the mother records when the baby moves. The doctor or midwife measures the response of the fetal heart rate to contractions and movements.

The difference in stress testing is that while you are being monitored, you will be given some form of oxytocin. Sometimes this is done by nipple stimulation or an injecction of Pitocin to induce contractions to see how well your baby responds.

When is it done: Usually done late in pregnancy.

Accuracy: Varies.

Risk to mom: Anxiety is most common over results.

Risk to pregnancy/baby: None known.

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