I have a girl who's heat is extremely hard to detect, you are lucky to find a single blood drop. I detected a single blood drop on Jan 25th and swabbed her daily for two weeks after and got nothing. I had her kenneled with the boy I wanted her bred with. Have been waiting for her to come into season and nothing since the blood drop, and no interest from my boy. Then suddenly last week she looked very pregnant. She is just started to loose some belly hair, full solid belly complete with sagging topline from puppy weight, nipple line very developed, temp today 100.6 .
Trying to determine her due date. I don't know if the blood drop detected on Jan 25th was the start of her heat, end of her heat, or maybe implantation bleeding. I can go by develment signs and taking of temps to watch for upcoming whelping. Has anyone had
temps of 100.6 earlier than approx 1 wk before whelping? I don't usually start taking temps till approx 1 to 1 1/2 wks before due dates so not sure if
they would have a normal temp prior to this time frame. Never did see my boy show interest...oh they were the sneaky pair

I'd ultrasound to see where pups are at with development. A good repro vet should be able to tell within a few days of due date.

The closest vet that can ultrasound or do progesterone tests is 2 hrs away. I'd hate to put her through the stress of a 4 hour drive this late in her pregnancy.

I asked the guy who is considered one of the best on the east coast how close they could get and he said "give or take a week."