Hello, I believe code 641.93 is correct.
using main terms in the alphabetic index Pregnancy, complicated, hemorrhage leads to code 641.9- using 5th digit 3 for antepartum as you stated. The 569.3 rectal bleed is not specific for the scenario and code 646.83 is "other" specified complications of pregnancy would be incorrect because you have the option of the specified indexed entry for hemorrhage complicating pregnancy (I noticed 646.8- in the index would be used for complication, pregnancy, gallbladder disease).
I hope this helps,
Elizabeth
CPC, CHONC, ICD-10-Proficient