I, myself, work for pathology and have done their coding for the last 19 years and when we get the placentas here, we use the codes
O43.90 (unspecified placental disorder, unspecified trimester)
O43.91 (unspecified placental disorder, first trimester)
O43.92 (unspecified placental disorder, second trimester)
O43.93 (unspecified placental disorder, third trimester)
We don't ever get denied using these codes (of course, only one of them, it's based on the trimester so whatever trimester they state, that's what you use unless it's not stated and that's where you'll use the unspecified). That's the only code that we use for the placentas here. To be honest, the majority of placentas we get here rarely have pathology that we can code so that's why we just go ahead and use one of these 4 codes
I hope this helps!!