Role of Maternal ABO Blood Type on Adverse Obstetric Outcomes
Authors: Shine Kailey , McGinnis Danielle , Iben Danielle , Holthaus Emily , Zoma Marim , Baran Kim , DeChristopher Phillip , Gylnn Loretto , Muraskas Jonathan 
Published: July 2024

Abstract: This retrospective chart review evaluates the potential role of maternal ABO blood type on various adverse obstetrical outcomes for both mother and neonate, including maternal hypertensive disorders, GDM, fetal growth restriction, clinical chorioamnionitis and other related disease processes. Methods: Delivery records were obtained from the electronic medical record (EMR) for deliveries occurring between 1/1/2020 and 12/31/2022. Data were extracted from nurse entered fields in the EMR during the delivery encounter (blood type, maternal age, body mass index (BMI), gestational age at delivery, quantitative blood loss, mode of delivery, and presence of Category 2 tracing,). Missing data were obtained through chart review. Other variables obtained through chart review included maternal pregnancy history, clinical chorioamnionitis diagnosis, fetal growth restriction, stillbirth, prolonged rupture of membranes, indications for cesarean section, hypertensive disorders of pregnancy, and medical history including chronic hypertension, gestational and pre-gestational diabetes, thrombophilia, bleeding disorder, venous thromboembolism, seizure disorder, cholestasis of pregnancy, and COVID infection. Comparisons between maternal blood type AB vs. all other blood types (group containing blood types A, B, and O) were completed using Student’s t-tests, Mann Whitney U tests, Pearson’s chi-square tests, or Fisher’s Exact tests as statistically appropriate. Comparisons between the 4 individual blood types (AB, A, B, O) were completed using ANOVA, Pearson’s chi-square tests, or Kruskal-Wallace tests as statistically appropriate. Post-hoc multivariate logistic regression was used to examine associations of interest identified on bivariate analysis. Results: A total of 3263 deliveries were reviewed from between 1/1/2020 and 12/31/2022. Of these, 113 patients had blood type AB (3.5%) and 3150 had other blood types (1015 type A, 463 type B, 1672 type O). Patients with blood type AB had statistically higher age than other blood types (31.0 ± 5.2 vs. 29.9 ± 6.1, p=0.046) and lower BMI (31.2 [IQR 7] vs. 33 [IQR 9.5], p =0.009). There were no differences in nulliparity, gestational age at delivery, chronic hypertension, gestational diabetes, cholestasis of pregnancy, quantitative blood loss, postpartum hemorrhage, clinical chorioamnionitis, fetal growth restriction, stillbirth, category 2 tracing, or mode of delivery. Patients with blood type AB had a gestational hypertension rate of 14% compared to 9% in other blood types (p=0.059). This association was further explored in multivariate logistic regression for prediction of gestational hypertension, which showed a statistically significant association for blood type AB vs. other (p=0.032, OR 1.91 (95% CI 1.06-3.43)) when controlling for age (p=0.074, OR 0.98 (95% CI 0.96-1.00)), BMI (p<0.001, OR 1.05 (1.04-1.07)), and gestational age (p=0.041, OR 1.06 (1.00-1.11)). However, patients with blood type AB had a rate of preeclampsia and superimposed preeclampsia of 3.6% compared to 8.9% in other blood types (p=0.05). This, too, was further explored in a regression for prediction of preeclampsia and superimposed preeclampsia, which did not show a statistically significant association for blood type AB vs. other (p=0.089, OR 0.36 (95% CI 0.11-1.17), when controlling for age (p=0.59, OR 0.99 (0.97-1.02)), BMI (p<0.001, OR 1.06 (1.05-1.08)), and gestational age (p<0.001, OR 0.88 (0.86-0.91)). A third regression model on any hypertensive disorder of pregnancy (including gestational hypertension, preeclampsia with or without severe features, eclampsia, and superimposed preeclampsia) did not show a statistically significant association for blood type AB vs. other (p=0.65, OR 1.13 (95% CI 0.66-1.95)) when controlling for age, BMI, and gestational age. Four-way comparisons between the 4 individual blood types (AB, A, B, O) did not show differences in any of the outcomes. Conclusion: Previous investigations have found variable results regarding maternal blood type and adverse obstetrical outcomes including hypertensive disorders, gestational diabetes, and perinatal diseases. A previous study by Burgess et al. found that mothers with type AB blood had an increased risk of developing late onset preeclampsia, while Hentschke et al. found no association between preeclampsia and maternal blood type. Reisig et al. found a significant correlation between type A+ mothers and the development of preeclampsia. This retrospective chart review of 3263 deliveries was performed to further investigate these associations and address this knowledge gap. It has been shown that AB blood type is associated with stimulated antigen response, an increased prothrombotic state and increased disease risk. In this study, maternal AB blood type was found to be associated with gestational hypertension. However, this association was likely due to a Type I error, as no other association with other hypertensive disorders, such as pre-eclampsia, was found to be significant. We found no other statistically significant correlations between maternal blood type and adverse obstetrical outcomes. Although previous studies have demonstrated a potential association between maternal AB blood type and adverse outcomes, our study, with a substantial sample size, did not yield similar results. In conclusion, physicians should not depend on maternal blood type as a reliable indicator of potential obstetrical outcomes or when identifying high-risk mothers.