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.
Doctors use several different methods to listen to the fetal heartbeat. About 3 weeks, one day after fertilization, when the heart first begins to beat, the sound of the little heart is too soft to hear. Very soon thereafter, they can see the motion using ultrasound technology. A doctor's stethoscope is not sensitive enough to hear the embryo's heart beating. A special stethoscope called a fetoscope works well when the fetus is larger, usually around 15-17 weeks. 1 An active fetus however, can make this method of listening a bit challenging.