Stopped bcps mid pack & had w/d bleed 4 days later. now pregnant - 1st moth off bcps will doc be able to accurately date pregnant w/o normal periods? how?

Yes, definitely: Pregnancies are easily dated with first trimester ultrasounds which are the most accurate way to date a pregnancy, especially when LMP is not known. They are typically accurate to within +/- 5 days. Don't worry for a second, you'll get a great date! call your doctor for appt soon.

Ultrasound Dating: The early OB ultrasounds are much more likely to give you accurate dating than relying on menstrual cycles. So, yes, with ultrasound.