Relationship between ABO blood group phenotypes and hypertensive disorders of pregnancy: A hospital-based cross-sectional study in Kano, North-West Nigeria

Background: Hypertensive disorders of pregnancy (HDP) complicate an estimated 5%–10% of pregnancies globally. Studies have linked non-O blood group with the development of HDP, especially preeclampsia (PE). However, these reports have not been consistent. This study aimed to determine the relationship between ABO blood group and HDP among pregnant women attending antenatal clinic at Murtala Muhammad Specialist Hospital, Kano, Nigeria. Materials and Methods: Two hundred and ten pregnant women with clinically diagnosed HDP and an equal number of age-matched normotensive controls were recruited for the study. Blood pressure was measured using a mercury sphygmomanometer and a Littman's stethoscope which was positioned on the medial aspect of the right arm at sitting position. Urinalysis was performed using a urine dipstick (Medi-Test Combi 9®). ABO blood groups were determined by tile agglutination method using potent monoclonal anti-A, anti-B, and anti-D reagents (Plasmatec Lab., Bridport, UK). Data were analyzed using Statistical Package for Social Sciences version 23.0. Chi-square test of association, Student's t-test, and logistic regression were used as statistical tools, and results were presented as frequencies, percentages, mean ± standard, odds ratio (OR), and confidence interval (CI); P ≤ 0.05 was considered statistically significant. Results: The mean age of the cases and controls was 26.20 ± 6.96 and 25.90 ± 6.37, P = 0.65, respectively. The mean gestational age of the cases and controls was 32.30 ± 4.15 and 29.06 ± 4.25, P = 0.01, respectively. The mean systolic and diastolic blood pressure of the cases and controls in mmHg were 176.62 ± 32.62 and 123.08 ± 6.40, P = 0.01, and 114.20 ± 20.08 and 76.43 ± 5.07, P = 0.01, respectively. Of the 210 individuals in the HDP group (cases), 90 (42.86%) had gestational hypertension (GH), 50 (23.81%) had PE, and 70 (33.33%) had eclampsia. Type O blood group was the most common group in both cases (93 [44.3%]) and controls (98 [46.7%]). This was followed by groups A (40 [19.0%] and 45 [21.45]), B (58 [27.6%] and 53 [25.2%]), and AB (19 [9.0%] and 14 [6.7%]) for cases and controls, respectively. There was no statistically significant difference in the frequencies of ABO blood group between the cases and controls (χ2 = 1.41, P = 0.70, df = 3). Compared to type O blood group individuals, non-O blood group individuals had 1.106 times odd of developing HDP than the controls (OR: 1.106, 95% CI: 0.753–1.625, P = 0.61). Similarly, types A, B, and AB blood group individuals had 1.292, 1.492, and 1.882 times odds of developing GH compared to blood Group O and controls (OR: 1.292, 95% CI: 0.670–2.490, P = 0.45; OR: 1.492, 95% CI: 0.813–2.740, P = 0.20; and OR: 1.882, 95% CI: 0.746–4.748, P = 0.18), respectively. Equally, types A, B, and AB blood group individuals had 1.243, 0.990, and 1.699 times odds of developing PE compared to blood group O individuals and controls (OR: 1.243, 95% CI: 0.561–2.754, P = 0.59; OR; 0.990, 95% CI: 0.442–2.217, P = 0.98; and OR: 1.699, 95% CI: 0.546–5.281, P = 0.36), respectively. Compared to type O blood group individuals, types A, B, and AB blood group individuals had 0.463, 0.690, and 0.901 times odds of developing eclampsia compared to controls (OR: 0.463, 95% CI: 0.199–1.079, P = 0.74; OR: 0.960, 95% CI: 0.505–1.825, P = 0.90; and OR; 0.901, 95% CI: 0.301–2.695, P = 0.85), respectively. Primiparity (OR: 2.320, 95% CI: 1.451 – 3.711, P = 0.01, for HDP) and gestational age (OR: 1.078, 95% CI: 1.013 – 1.148, P = 0.02 – gestational hypertension; OR: 1.328, 95% CI: 1.212 – 1.456, P = 0.01 – preeclampsia; OR: 1.467, 95% CI: 1.333 – 1.614, P = 0.01 – eclampsia) were identified as pregnancy related risk factors for HDP. Conclusion: The frequencies of ABO phenotypes in women with HDP are similar to that of normotensive pregnant women. There is no relationship between ABO phenotypes and HDP as observed in this study. However, nulliparity and gestational age were identified as risk factors for HDP. Similar hospital-based and population-based studies should be conducted to further evaluate this phenomenon in this environment.