ultrasound at day 30 reliable

Question
I had my yellow lab ultrasound at day 30 and the vet could only pick up 3 maybe 4 puppies.  How reliable is this?  I have bred before, this is her second litter.  None of my females have had a litter smaller than 7 and we have used the same male.  

Answer
Hi Shirley

Personally, I still find x-ray more reliable. You can count skulls and actually see where the pups are placed. X-rays are done after 50 days.   With ultrasound, there is always the chance that there are pups behind each other and not easily detected.

Also on a side note, the older a female gets the less viable her eggs. It's the female that determines how many pups as she is born with all the eggs she is ever going to have.

Good luck.