Arterial Blood Gases. Test Overview. An arterial blood gas (ABG) test measures the acidity (pH) and the levels of oxygen and carbon dioxide in the blood from an artery. This test is used to check how well your lungs are able to move oxygen into the blood and remove carbon dioxide from the blood.
How Often the Test Is Done During Your Pregnancy. Your doctor may use the Doppler often to listen to your baby's heartbeat during routine checkups, starting at about 8 to 10 weeks. Handheld Dopplers will not work quite this early.
Throughout a woman's pregnancy, her doctor will typically begin a prenatal exam with listening to the baby's heartbeat. Although a Doppler instrument is most frequently used, a fetoscope, a type of stethoscope, can be used after 20 weeks to hear a baby's heartbeat. A baby's heartbeat is checked often to monitor how the baby is developing and coping with the stress of the pregnancy and labor.