Massive transfusion in relation to obstetric hemorrhage : with special attention to placenta accreta

Abstract: The overall purpose of this thesis was to assess risk factors, incidences, and complications of massive blood transfusions in relation to obstetric hemorrhage postpartum. Obstetric hemorrhage requiring blood transfusion postpartum has recently shown an increasing trend in many high resource countries. Massive transfusion, defined as more than 10 units of RBC within 24 hours is well described in surgery and trauma care, however little is known about its occurrence and risk factors in obstetric patients. Most blood transfusions are safe and necessary, but there are potential complications, including transfusion reactions, transfusion transmitted infections, and post transfusion thrombosis, which have to be taken into consideration when choosing between blood transfusion and other alternatives. The increasing rate of cesarean deliveries since the 1970’s, has contributed to complications in sequential pregnancies. One of the more severe complications is abnormally invasive placenta, a condition with a high risk of requiring massive blood transfusion and peripartum hysterectomy. In Study 1, the incidence, risk factors, and rate of antenatal detection of abnormally invasive placenta in the Nordic countries were investigated. The study was conducted as a Nordic collaboration from 2009 to 2012, and included 605,000 deliveries. Cases of abnormally invasive placenta were reported on a monthly basis directly from maternity wards, and were complemented with data from the National Health Registries to confirm or to identify missing cases. In total, 205 cases of invasive placentas associated with a laparotomy were identified, corresponding to a prevalence of 3.4 per 10,000 deliveries. Major risk factors were placenta previa (OR = 290) and prior cesarean section (OR = 7). Only one third of the cases identified as invasive placentas were detected antenatally, and among those cases not detected, more than one third had had a prior cesarean section. Study 2 was a retrospective population-based cohort study investigating risk factors, incidence, and trends over time for massive blood transfusion in women who gave birth in the County of Stockholm between 1990 and 2011. Data from the Medical Birth Registry was cross-linked to the Stockholm Transfusion Database. Massive transfusion was defined as transfusion of >10 units of red blood cells from time of partus through the next day. Altogether 517,874 pregnancies were included. The study found the incidence of massive transfusion to be 5.3 per 10,000 deliveries and showed an increasing trend over time. Major antenatal risk factors were abnormal placentation (OR = 41) and prior cesarean section (OR = 4). Study 3 was a retrospective cohort study investigating whether postpartum hemorrhage and red blood transfusion are significant and independent major risk factors for venous thromboembolism postpartum. Women who gave birth between 1999 and 2002 in the Stockholm region were included in the study. A time period before the implementation of national thromboprophylaxis guidelines was chosen. Data from the Medical Birth Registry was linked to the transfusion database and to the National Discharge Registry. Among 82,376 deliveries 56 cases of venous thromboembolism were identified. The study found transfusion of red blood cells postpartum (OR = 5) - but not postpartum hemorrhage without blood transfusion - to be a significant major risk factor for venous thromboembolism postpartum. In Study 4 the aim was to assess the risk of transfusion reactions in women receiving postpartum blood transfusion. This populations based cohort study is based on the same cohort as Study 2. Data on pregnancies from the Medical Birth Registry was linked to the Stockholm Transfusion Database. Women with postpartum blood transfusion and a transfusion reaction within seven days from partus were identified. The study found a twofold increased risk (OR = 2.0) of a transfusion reaction in women postpartum compared to non-pregnant women receiving a blood transfusion. Among all women who had a blood transfusion postpartum, women with preeclampsia were twice as likely to have a transfusion reaction. In summary, abnormally invasive placenta occurs in 3.4 out of 10,000 deliveries and is the major risk factor for massive blood transfusion postpartum. A reduction in the rate of cesarean deliveries might be the best way to lower the incidence of both invasive placenta and massive blood transfusion postpartum. A focused ultrasound in pregnant women with a placenta previa or a low-lying placenta covering the scar of a previous cesarean section might improve antenatal detection of abnormally invasive placentas and allow better planning for delivery, thereby reducing maternal morbidity in those complicated pregnancies. Postpartum blood transfusion and especially massive blood transfusion are independent major risk factors for postpartum thromboembolism. As such, they should be implemented in the Swedish thromboprophylactic guidelines during pregnancy. The risk of transfusion reactions in women during pregnancy seems to be increased, especially in pregnancies complicated by preeclampsia. Therefore, a heightened attention is recommended to women with preeclampsia when a blood transfusion is to be administrated.

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