Recent findings have provided support for the treatment of cancer during pregnancy, a coincidence that places both mother and fetus at risk. Our objective was to critically review studies on physiological variations during pregnancy of the most commonly used tumor markers in the diagnosis and monitoring of gynecologic cancers. We performed a systematic review of three tumor markers during normal pregnancy: namely CA15-3, CA 125 and lactate dehydrogenase. For CA 15-3, 3.3% to 20.0% of all measurements were above threshold (maximum 56 U / ml in the third trimester). 35% of CA 125 were above cut-off: highest level in the first trimester, with a maximum value of 550 U / ml. Lactate dehydrogenase was not elevated in maternal serum during normal pregnancy. During normal pregnancy, tumor markers including CA 15.3 and CA 125 may be elevated; lactate dehydrogenase values remain below normal values. Knowledge of physiological variations during pregnancy may be important.