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.
The test is like standard echocardiography except that the pictures of the heart come from inside the esophagus rather than through the chest wall. The sound waves are sent through the body with a device called a transducer, which is attached to a tube and put down your esophagus. The sound waves bounce off of the heart and return to the transducer as echoes. The echoes are converted into images on a television monitor to produce a picture of your heart and aorta.