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.
Plethysmography uses blood pressure cuffs or other sensors attached to an instrument called a plethysmograph (or pulse volume recorder) to measure changes in the volume of a limb (or extremity). Because these volume changes are directly related to the amount of blood flowing through the limb, plethysmography helps to identify problems affecting blood circulation.