Possibly you're temperature drop is on it's way! Have a look at this, I think it explains quite well:
http://www.debbiejensen.com/temp_chart.htmlI do find the temperature method very accurate for me, as does my breeder friend/mentor. I'm not sure what you mean by a 'significant' drop. I'm just looking for a drop into the 36Cs, just as an example, the lowest I recorded on this year's litter was 36.7 at 0300 on the Saturday, she whelped at 2335 that night. I may well have missed a lower drop as the previous temp taken at 10pm on the Fri was 37.3, the temp taken on whelping day at 1145 was on the rise again!
The lowest on another litter was also 36.7 and she whelped within 24 hours, again the temperature prior to whelping was on the rise.
A dog's normal temperature is around 38.6C, so 38 isn't to be worried about. Whilst you are saying 37.7 for your girl's normal temperature, that's only been taken whilst pregnant, if I'm reading your post correctly. Post whelp it may be in the range of 38.3-39.4. If it's more than that then that's when I start to worry :-O
I'd say don't get too hung up with the temperature thing, it's just a guide to help you judge when the pups will start arriving, and can be nicely used alongside other signs. But if I were recording your temperatures, I'd now be monitoring to look for the steady drop and my guess is that you're looking at another 48 hours. But, don't hold me to that, I don't know your dogs, I don't know your thermometer, I don't know your thermometer reading skills, I don't know your room temperature, and I don't know anything else should she be a week overdue :-O But if she were mine that's what I'd be sort of expecting ;-) ... hhmm, wondering if I've given a sufficient get out clause!
I am wondering what the temperature is this evening.
Oh, my girl ate a lovely big lunch on the day of whelping :-O So, if she eats don't rule whelping out! Oh, also, my girls have never been sick prior to babies ;-)
How exciting, I hope all goes well, I am sure it will do ;-)