Pregnant Sow

Question
I have owned several boar guinea pigs in the past but bought my first sow/female on January 21st of this year.  I have not owned a guinea pig for about 10 years and never a female.  After about 4 weeks I noticed a drastic change in her midsection. And thought oh great I bought a pregnant guinea pig.  I know nothing of breeding guinea pigs. It's never been my intention.  Well it is now May 16th. She is very large. Nipples r large.  She was seen by the vet today and her pregnancy is confirmed. It is not false and has at least 3 fetus.  She is still very active. Loves attention. Eats and drinks a lot. She has not been around any guinea pigs since the day she was purchased.  This would make her being 117 days into gestation IF she conceived on the day I bought her. Is this even possible?? Can a female guinea pig hold sperm until its the right time to b pregnant??  I'm just confused. Vet said she is very healthy. Truely pregnant and just to watch her close. So my question is as above. Can they hold sperm for a later pregnancy or can there be a rare case of a longer gestation?  

Thank you for your time.
Stacy

Answer
This is something I've never heard of, but I suppose nothing is impossible. The normal gestation is about 70 days. To answer the question about holding sperm, no. Sperm from any species does not live that long so that wouldn't be possible.

This may be a case of rare gestation, maybe something for the Guinness Book of Records!