Ay, first time ko marinig yan phrasing, pero I think you mean baby is lying on or very close to the placenta? Honestly sis, sa 17 weeks marami pang malaking changes sa positioning, so don't worry too much yet, the baby moves around a lot pa, kaya likely mag-shift pa yan by the time you're further along. Best to ask your OB directly about it sa next visit para ma-explain niya exactly what they saw, kasi sometimes the angle of the ultrasound or how baby is positioned makes things look different than they actually are, and doctors will know best kung may kailangan i-monitor or kung totally normal lang yan.