Welcome! My name isXXXXX am a 2003 graduate from UC Davis, and currently a Medical Director of a veterinary hospital.
I am sorry to hear about this concern.
Well, that size disparity could predispose to dystocia (difficulty birthing) and a need for C-section.
But, it has only been a few hours. Whelping
.Multiple Links on Newborn Care
.Dystocia Link (Difficulty with Birth)
.General Pregnancy Information
I want you to pay specific attention to the link about dystocia.
Also, I think the following information about time intervals will be useful as well.Labor Timing
You'll see that labor can be up to 12 hours. But, now that she is in labor, if you see her having contractions but then after a period of time she seems to stop, that may be due to getting tired or weakness. That will be a red flag that warrants emergency attention.
One option is to get into a vet right now! Get an x-ray to determine if the fetus lined up to come out first is too large. That will give you the knowledge to know if C-section should be started immediately.
Hope that information has been helpful.
Please remember to select Reply to Expert, if for any reason you need further clarification, have more questions, or were expecting a different type of answer. Prior to leaving a feedback rating, which I greatly appreciate, my goal is to provide you the best answer possible.