I've reliably been able to get a dark + at only 9 dpo with each pregnancy...both singles and twins. THe earliest I've ever gotten one was very late on day 8. That was with my 8th and she was a single baby. All of my others have been right on morning of day 9. With this pregnancy I tested at 8 dpo, 9dpo and 10 dpo...all with negatives. We went out of town and I retested at 12 dpo and still a negative. On 13 I got a - in the am but a VERY faint + that took 5 minutes to appear in the afternoon. Same result on day 14. I quit testing thinking I would begin bleeding anyday. When I failed to start my period I tested again 7 entire days later and it was finally dark and strong. I measured 2 cms smaller than average up until 16 wks. At 21 wks we discovered our 2nd set of very healthy, thriving twins actually measuring a couple of days ahead of 21 wks! So, I have learned that tests and the strength and swiftness of the line mean nothing as to how many are in there!!! LOL!