Hi,  I have some concerns about my pregnant pony.  She's 1/2 shetland 1/2 mini and stands about 42" tall and I bred her the first 2 weeks of July '07.  According to the horse pregnancy calculator she's due in about 4-6 weeks and this little mama is huge.  This is her 2nd colt and the last one I bred her to a 52" welsh stud and had a nice size baby, but I don't remember her being this big.  So I'm wondering if she's having twins.  Most everything I have read about twins isn't good for neither the mother nor the babies. 

Does anybody have any info or has anybody had any twin babies?  She is an easy keeper so maybe she's "just healty" as my grandmother would say.  I'm sure the vet could do an ultrasound on her and it would be a bit costly but I also don't want anything to happen to her.  If anybody has any info I would appreciate it, and thanks in advance.