I think my sisters guinea pig, Butters, is pregnant by my guinea pig, Reeces.

Question
Dear Pat,

I've had my guinea pig for about 2 months or less and same has my sister. We got our guinea pigs from PetSmart. They were both in the same cage and we THOUGHT they were both males. about 9  days, we went to PetSmart to get guinea pig stuff and I ran across a pen where the guinea pigs could run around in. We came home and set it up and when we put our guinea pigs in, mine started humping my sisters. After 10 sec, Butters ran away. We were all astounded by what just happened. So we took them to the vet and found out Reeces is a male and Butters is a female. I'm wondering that maybe Butters might be pregnant. I know about females going into heat and I know about all that stuff. I did my research and I think she has the symptoms of pregnancy but not all of them. Shes round and she has a hard abdomen. My mom said she isn't but I would like a experts point of view and would like to know about all the symptoms and what goes on every week of pregnancy... btw my mom isn't vet or a guinea pig expert so I need help.

Answer
Are you saying that the two of them have been together in the same pen all this time or just recently? Guinea pigs don't come into heat on a regular basis. Usually they are in estrus (a fancy name for being in heat) for only a few days. It's not a regular cycle, some will come in every two weeks, some as long as three weeks. They may only be receptive for a couple of days.  So it's difficult to predict when pregnancy may occur.

Even if the sow is not in heat the boar will mount them and try their luck. If they've been together since you got them the chances are greater than not that Butters is pregnant. Of course the question is by whom? She could have gotten pregnant before she left PetSmart. If they were only together for a few minutes the chances are far less that she conceived.

The gestation period is roughly 70 days. If she is pregnant you will feel babies moving around two to two and a half weeks before delivery. Not usually before then.  The females don't often look very pregnant until late in their pregnancy.  Within about a month into the gestation they tend to drink more water. Other than that there aren't many signs indicating babies. They do get a pear shaped figure and the tummy gets firm but that's about it. It's really a wait and see time.

There isn't anything special you need to do for Butters. She will take care of everything herself. You can safely hold her until she's obviously heavy with child, then it would be uncomfortable for her to be handled.

I'm not sure if this is really help for you or not.  Time will tell if you're going to have little ones in the family.  The usual litter is only two or three, although single births are common as well.  So are stillborn babies.  Don't be surprised if she has a dead baby in the litter. It's just the way it is and has nothing to do with how you've cared for her or fed her.