Measuring different

Hello ladies! I know I’m probably just being a little *crazy* buuuut I had my first ultrasound with the MFM doctor on Monday (13w4d). Babies are Di/Di. Baby A measured 12w5d days heartbeat at 175 and Baby B measured 13w3d heartbeat at 159... does this sound about right? This is the first time they’ve measured so far a part and it has me a little worried...and no the ultrasound tech didn’t say anything but they aren’t supposed to.