this can be a very difficult situation, both for the patient and the doctor.
Leaving the placenta in its place and giving methotrexate has been proposed, some report very successful outcomes with spontaneous resorption of placenta, and some report late post partum hemorrhages even necessitating hysterectomies. Surgery is always an option and rather than going into surgery in emergency, elective conditions should be seeked. Daytime surgery with blood transfusion support should be preferred. If you don't have a multidisciplinary support team, consider transporting the patient to a tertiary center before the labor starts. Good luck
Depending on the size of the retained placenta, is the entire placenta or just a lobe? Depending on the patient status, is she thermodynamic stable, not bleeding or is she profusely bleeding?
Medical management can be attempted in stable cases with small retained placentas but the patient should be closely followed as she is at risk of infection which could become very serious.
You can always do a controlled hysterectomy if the patient has completed her family and you are located in a hospital that can provide you with the necessary amount of blood.
If unstable than hysterectomy is the only option. If you're not able to do so at your hospital then tamponading the uterus can be attempted and transport the patient to a facility that has the capability to do the hysterectomy and transfuse the patient.
a retained placenta or persistent postpartum bleeding develops after vaginal delivery. After reassessment of the risk factors for placenta accreta, the possibility of abnormal placental invasion must be considered before proceeding with additional attempts at manual or surgical removal because these may only worsen the hemorrhage and increase the risk of maternal morbidity and mortality. When the diagnosis of placenta accreta is suspected, management options might include intrauterine balloon tamponade, selective pelvic embolization in stable cases, and emergency surgery