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Between 8 and 10 weeks of pregnancy, your doctor performs an ultrasound to check the baby’s health and development. Ultrasound helps your doctor to determine how far along the pregnancy is.

During an ultrasound, warm gel is rubbed onto your abdomen. A scanning device is then placed on your abdomen, and sound waves transmit images of the baby and the amniotic sac to a high-definition monitor. Sometimes, the due date is adjusted based on the results of this test. The baby’s skull, arms, and legs are evaluated.

A nuchal translucency screening is done at this time to measure the thickness of the baby’s neck, which can be a sign of conditions such as Down syndrome. Further testing, such as chorionic villus sampling (CVS) or amniocentesis, is then performed to confirm or rule out this diagnosis.

Ultrasound tests can also detect the baby’s heartbeat, typically at six weeks. At 16 to 22 weeks of pregnancy, ultrasound testing provides detailed views of the baby’s internal organs, including the brain and the heart. In the third trimester, ultrasound may be used to help your doctor assess the baby’s size prior to delivery.

Your doctor tests you for gestational diabetes between 24 and 28 weeks of pregnancy, or sooner if you are at risk. Gestational diabetes, which can cause high blood pressure, can be a cause of excessive birth weight, which is when a baby is nine pounds or heavier at birth, increasing the need for a cesarean delivery. It can also increase the baby’s risk for metabolic problems—resulting in a rapid heart rate and breathing—and jaundice, which is when there is a yellow discoloration of the baby’s skin, after birth.

In this test, you drink a liquid form of glucose that causes your blood sugar levels to rise within 60 minutes. If your blood sugar level is higher than 130 milligrams per deciliter, you then take another test.

For 8 hours prior to the second test, you must fast, meaning you do not eat or drink anything. During this test, you drink glucose. Then, your blood is tested immediately and every hour for three hours. If two of the four blood glucose levels are found to be elevated, you have gestational diabetes.

Your blood sugar levels must be tested upon wakening and after each meal during your pregnancy. You can do so by using a home monitoring device that measures a drop of blood taken from your finger.

You may require insulin to control blood sugar levels and to avoid the complications of gestational diabetes, such as excessive birth weight in the baby.

Group B Streptococcus is a bacterium that can be found in the vagina, urinary tract, or rectum. It can be passed to the baby during delivery and cause serious illness. Your doctor tests you for group B strep between 35 and 37 weeks of pregnancy, or sooner if you’re at high risk of preterm labor.

If you test positive for group B strep, your doctor gives you intravenous (IV) antibiotics during labor to prevent infection of the baby.

If you are at high risk for pregnancy complications, including preeclampsia, or if you are carrying more than one baby, you may have fetal monitoring tests to evaluate the wellbeing of your baby or babies. These tests are conducted during the third trimester.

A biophysical profile test is used by your doctor to evaluate your baby’s breathing rate and muscle tone, as well as the amount of fluid in the amniotic sac. This is done using ultrasound.

If this profile determines there are problems with the baby’s wellbeing, a nonstress test may be performed. During this test, a monitor attached to a band is strapped around your abdomen to measure the baby’s heart rate and movements. Every time you feel the baby move, you press a button attached to a monitor. If the results show little movement, you may take the test again to help assess whether the baby is in distress.

Your doctor may perform genetic testing to assess the baby’s risk of certain conditions if you are age 35 or older, or if you had another baby who was born with genetic irregularities. These tests also may be performed if an ultrasound scan indicates a birth defect such as a congenital heart defect. If tests indicate that the mother is a carrier for a genetic condition, the father’s blood may also be tested.

Cell-Free Fetal DNA

In a cell-free fetal DNA test, your blood is tested for chromosomal abnormalities in the baby. This is possible because cells from the placenta, an organ that provides nutrients to the baby in the womb, circulate in the mother’s blood. A positive test result can indicate genetic conditions such as Down syndrome.

Chorionic Villus Sampling

Between 10 and 14 weeks of pregnancy, your doctor may perform chorionic villus sampling, or CVS, which is a test for genetic abnormalities, such as Tay-Sachs disease, or chromosomal problems that can cause conditions such as Down syndrome.

In this test, the doctor inserts a thin, flexible tube called a catheter through the vagina into the cervix and placenta. Sometimes, a long, thin needle is inserted through the abdomen instead.

Ultrasound helps guide the doctor to the placenta, where he or she collects a sample of chorionic villi, tiny growths that carry genetic material. This sample is tested in a laboratory.

Rarely, a CVS test can increase the risk of miscarriage. Often, this test can be performed instead of amniocentesis, which is not performed until the second trimester.

First Trimester Screening

Between 11 and 14 weeks, a series of blood screening tests are performed to determine the baby’s risk for certain chromosomal abnormalities. One test determines levels of pregnancy-associated plasma protein A, the results of which can help your doctor assess the risk of miscarriage or low birth weight in your baby. Your doctor may also perform tests that determine the level of a pregnancy hormone called human chorionic gonadotropin. Low levels can indicate miscarriage or ectopic pregnancy, and high levels can indicate pregnancy with multiple babies.

The results of these tests, in combination with nuchal translucency screening performed with ultrasound, help identify the baby’s risk for Down syndrome and other chromosomal abnormalities.

Amniocentesis

An amniocentesis can test for genetic abnormalities, such as Down syndrome and cystic fibrosis. It can also determine if a baby has certain birth defects, including neural tube defects, which affect the baby’s brain and spinal cord.

In this test, a sample of amniotic fluid, which surrounds and protects the baby in the womb, is taken for analysis. A thin needle is inserted through the abdomen and into the uterus to the fluid-filled amniotic sac. A small amount of amniotic fluid, which contains cells, is extracted and analyzed in a laboratory for irregularities.

This procedure is performed after 16 weeks of pregnancy. Rare complications include amniotic fluid leakage, which can cause an infection in the mother’s uterus, and miscarriage.

Multiple Marker Screening

Also known as the quad screen or modified sequential screen, this blood screening procedure identifies four substances: alpha-fetoprotein, a protein produced by the fetus; human chorionic gonadotropin; the hormone inhibin A; and estriol, an estrogen produced by the baby. The results of this test can help determine if the baby has certain genetic conditions. It is performed between 15 and 22 weeks of pregnancy.