doppler at 16 weeks

Hi all!! Haven't posted here in a while, since I went back to LTC. Anyway, question! One of my friends, who currently works postpartum, is having trouble with a 16 weeker, in for dehydration. She has had her for around 48 hours, and no one has been able to get a FHT with a doppler. They are trying twice a shift, so basically QID. She does have an anterior placenta according to last ultrasound, and they can hear placenta noise, but no baby. The OB is reassuring her that it is normal not to hear for a prolonged period at that gestation and hasn't ordered an ultrasound or done a bedside at this point. My friend has been pp, and done L and D, forever, and has never not been able to hear for this long with a doppler. I've never not been able to hear and not have the OB order an ultrasound, at least for mothers peace of mind. Have any of you guys ever had this situation come up?