Dr. B,
Thank you so much for your response, it was very reassuring. The baby is moving around a lot and follow up scans were fine. I was thinking about what you said and wonder if there are effects on the mother too-during my last pregnancy, in my third trimester, every time I leaned back or went on my back I would feel strange and parts of my field of vision would be gone and it would last a few hours. Also I have on occasion fainted after standing up too quickly (not while pregnant) and now while pregnant I have to be careful because I feel woozy if I do that.
Oh-and it's a girl!
Hi!
It is very common for the fetal heart rate to drop transiently--we see it all the time on ultrasound or on the fetal monitor later down the road.
When a woman is pregnant and lying on her back, the large uterus ( about a cantelope right now) compresses her vena cava ( a huge vein which brings all of the blood from the lower part of the body to the heart) against her spine. Kind of like parking your car on the garden hose. This results in a drop in mom's blood pressure and a reduction in the blood supply to the baby. The baby's heart rate drops too in response to the lower blood supply. Turning onto the mom's left side will correct the problem almost immediately. Some women are more sensitive than others, and you may be one of the sensitive ones.
It doesn't hurt the baby--its just like holding your breath for a minute.
Whenever you lie down, if possible, keep a small pillow or folded towel under your right hip to prevent this from happening too often.
Good luck--by the way--did you find out boy or girl?
Dr B