Carbon Dioxide (CO2)

Monitoring CO2 is essential, as abnormal levels can reflect metabolic changes and nutritional deficiencies. This article will discuss the optimal CO2 ranges during pregnancy, explore the causes of high or low levels, and examine how pregnancy’s physiological shifts influence these reference values. 

CO2 Testing

The CO2 test measures the concentration of bicarbonate (HCO3⁻) in the blood. Approximately 95% of CO2 is in the form of bicarbonate. Therefore, the CO2 blood test is really a measure of the blood bicarbonate level.

CO2 is the byproduct of cellular respiration. In normal metabolic function, glucose enters the citric acid cycle to be metabolized to make adenosine triphosphate (ATP) energy. Energy production requires H2, O2, and glucose and is catalyzed by several enzymes that rely on B vitamins for function. CO2 is one of the byproducts of this process. CO2 is transported through the bloodstream in a bicarbonate-bound form. CO2 is negatively charged and works as a base in the body to regulate pH. 

The chloride shift is the process by which chloride and CO2 are exchanged in red blood cells for oxygen and CO2 transport. When CO2 enters the plasma as a byproduct of cellular respiration, it dissolves and degrades to bicarbonate. Red blood cells exchange this bicarbonate for chloride. When RBCs enter the lungs, the opposite occurs, which releases CO2 for exhalation, adding chloride back into the RBCs. 

CO2 in Pregnancy

Gap metabolic acidosis results from bicarbonate losses through the gut or kidneys with subsequent gain in chloride ions. [1]

During pregnancy, and especially during labor, the maternal carbon dioxide level declines considerably.

Renal adaptations that cause increased excretion of bicarbonate during pregnancy are reversed immediately after delivery, leading to the reabsorption of bicarbonate and a rise in CO2.

High CO2 in Pregnancy

​There is limited data on the application of this indice in pregnancy.

Most Common Causes of High CO2 in Pregnancy

• Metabolic Alkalosis
• Acute Illness w/Fever
• Severe Vomiting in Pregnancy (Hyperemesis Gravidarum)
• Asthma
• Sleep Apnea/Snoring

Low CO2 in Pregnancy

​There is limited data on the application of this indice in pregnancy.

Most Common Causes of Low CO2 in Pregnancy

• Dehydration
• Thiamine Deficiency
• Metabolic Acidosis

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Medical Disclaimer:
This content is for educational purposes only and is intended for licensed medical professionals. It is based on current research, subject to change, and not intended to diagnose, treat, or prevent any medical condition. This information does not replace consultation with a qualified healthcare provider. Seek professional medical evaluation and treatment from a licensed provider. Use of this information is at your own risk.​

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