I am 15 1/2 weeks pregnant with twins, and have been spotting for over three weeks. The spotting only happens when I am lying down, on my side and it is always heavy, meaning it fills a pad. It is very similar to a menstrual period, but I can't tell if I'm cramping because I have overwhelming back pain. My doctor tells me not to worry, but I do every time I wake up and I feel the bleeding. I'm starting to fear lying down at night. According to one ER doctor, the blood seems to be coming from my cervix, which also seems to be irritated. Have you encountered anything remotely similar to this? My blood pressure and pulse are normal. The babies are moving and breathing normally, too.
Yours is a very interesting question. (Although I know it's no fun to be medically interesting!)
I can only guess at what's happening. Since you're in the 2nd trimester, you're out of miscarriage territory. But with so much placenta involved with twins, I wonder if you've had an ultrasound to rule out a placenta previa. This would explain your bleeding, but not why it seems to be positional.
If you have cervicitis, an irritation on your cervix, this could also explain the bleeding and is in fact the most likely cause. Here's where my guess work come in: With your uterus being third trimester size (because of 2nd trimester twins), it's possible that you have some prolapse of your cervix, and if this causes it to jut against your vaginal floor (or roof, or sidewall), this may stop the bleeding; yet when you recline, the pressure of the cervix isn't jammed against your vagina, allowing it to ooze freely.
First and foremost, ruling out a previa is my first thought. If you don't have that and the babies look fine, then your doctor is right to ignore the problem. If you wanted to get aggressive with the cervicitis, you could have a vaginal smear done to rule out yeast or bacterial vaginosis infection--both harmless, but causes of cervicitis.