Pregnancy and propane fumes?

The past few days, I've noticed an odor coming from my propane heater whenever it ignites. This concerned me since I'm 8 weeks pregnant, so I purchased a Carbon Monoxide detector. CO was not detected. I had my landlord check for leaks today. There weren't any, but my tank was very low on propane. He had explained heaters and stove that run on propane will often emit an odor when the tank almost empty. I am wondering if the odor would be harmful to the fetus.