Is it true you can get pregnant from pre-cum on your period?

Maybe but: The totally precise, correct, exact answer is "we don't know." we don't know because no one has (or will) ever study this in a scientific manner. It would be extremely unlikely, but under some circumstances it's theoretically possible. So "maybe" you could. Use protection if you don't want this to happen. If 47 years - if - is your correct age - then the chance is basically zero.

Very unlikely - if a: female has a very short menstrual cycle - maybe. Most studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile (however, don't know how promptly samples were examined). One small study published in 2011 showed that there are some individuals with a high motile sperm count in pre-ejaculate. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564677/