That's odd. I am a guy, not pregnant lol and I wear mine on the front side of my stomach but I sleep on my stomach so we are pretty much doing the same thing. My reciever never misses a beat. I will however say that I have a few lycra workout shirts I use that dramatically affect the readings. Could it be you have some bed clothes that might be causing interference?
I've had bad readings from the G4 when wearing on my side between the bottom of the rib cage and the top of the hip. It sometimes goes way high or way low, both rapidly as you observed.
I attribute this to times that I am sleeping on the sensor and compressing it against my mattress. When I download to Dex's Studio software, the anomalous data has a characteristic signature, a rapid surge up or down, often followed by missed data points. It's as if the Dex brains knows something is askew and it goes offline trying to figure it out.
I always fingerstick when this happens as I've learned the hard way that dosing or adding carbs based on the Dex alone only makes matters worse.
As to alternate sensor locations, have you tried the back of your upper arms? I've had mixed results there but I've read some reports of consistent success with good readings.
Good luck with your pregnancy! I'm always awed by the heroic efforts that T1D women make when they successfully manage their BG during pregnancy.
Try wearing it on your upper arm, just beside your shoulder. You won't sleep on it... that might help.
I was just about to post a similar question! I am at the beginning of my second pregnancy. With #1, I wore the 7+ sensor in my thigh with great results! If you put your legs together, I put the sensor at the midpoint between my knee and hip, on the inside, but above where my thighs touch (if that makes sense!). It gave me the heebie-jeebies to think about it, but insertion was not painful and my readings were great.
Here's the rub. I tried over the weekend in my thigh and two sensors failed there. Not sure if it's a g4 thing or just my luck. I was hoping someone would chime in and say they get great results in the inner thigh and it would give me some hope to try again.
Currently I use my upper arm, flank, and upper buttock areas for my omnipod so that real estate is taken...