I don't think I would read into how dark the lines are on a positive pregnancy test. The fact is that if there is a positive, it means positive, no matter how dark the line is. Some women produce different amounts of hCG (which is the hormone detected in pregnancy tests).
It is true that with twins, you will have higher levels of hCG. But that really depends on each person.
I am now 20 weeks pregnant. When I first got pregnant (this time) I took a pregnancy test at what would have been 5 weeks pregnant. I got a negative. I took multiple tests during the morning for the next week and got all negatives. However, at 6 weeks, I finally got a positive pregnancy test, and that positive was still somewhat faint.
Because I had a previous miscarriage in my first pregnancy and I had had so many negative tests, at the doctor, after seeing that my pregnancy test showed positive, my doctor ordered that we draw blood to check where my hCG levels were at. Of course, we had to check them after 48 hours as well. When I went back to have my blood drawn the second time, my doctor said that my hCG levels were REALLY low and that didn't indicate a viable pregnancy, but that we would check to make sure that they doubled. I remember him saying "if this is viable, you are really, really early! like 2 and a half weeks pregnant!" I knew that that wasn't right. Anyway, when the second blood draw came back, my hCG levels had, in fact, doubled in 48 hours. The next week, when we did a dating ultrasound (my doctor thought that I would be so early that we wouldn't see anything via ultrasound), we saw a 7 week 3 day old fetus! For whatever reason, I had produced a very low amount of hCG but I'm now 20 weeks and haven't had any complications. Lord willing, we will have our baby with us in April.
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