BRIEF COMMUNICATION ABO blood group and fertility: a single-centre study Carlo Mengoli1, Carlo Bonfanti2, Chiara Rossi2, Massimo Franchini2 Faculty of Medicine, University of Padua, Padua; 2Department of Transfusion Medicine and Haematology, "Carlo Poma" Hospital, Mantua, Italy
The overall number of the women included in the study, which was performed at the Transfusion Centre of Mantua City Hospital (Italy), was 7,250; the sizes of the three cohorts are reported in Table I. The Pearson's chi2 test on all three cohorts was significant [Pearson's chi2 (6 d.o.f.)=13.73, p=0.033] (Table I). The significance was
The ABO blood group exerts a profound influence on haemostasis, documented by the close relationship between ABO blood type and von Willebrand factor (VWF), and hence factor VIII (FVIII), plasma levels1. Individuals with blood group O have approximately 25% lower VWF plasma levels compared with those with non-O blood groups2. Among people with non-O groups, AB individuals have the highest VWF and FVIII levels, followed by group B and then group A2. Several epidemiological studies and systematic reviews have analysed the clinical consequences of this phenomenon, especially regarding the risk of developing venous and arterial thromboses3-5. However, beside the association with various pathological processes, it would also be interesting to know whether the non-O blood type-related enhanced clot formation, documented by thrombin generation tests6, is also able to influence some physiological processes linked to haemostasis7. A possible relationship between ABO blood group antigens in women and uterine embryo implantation is particularly intriguing. With the aim of investigating the effect of ABO blood group system on female fertility, we conducted a single-centre study evaluating the correlation of ABO blood group system in female blood donors with and without children and in pregnant women.
A Cohen-Friendly association plot was built with R8,9. The age distribution in the three cohorts was explored, in order to detect age as a possible cofounder. Age was compared in the three cohorts by the ANOVA approach, followed by a pair-wise comparison of the three cohorts. In order to evaluate the possible effect of age on the prevalence of the four blood groups (A, B, AB and O), a multivariate logistic approach was followed, using each blood group as a dependent variable, and age + cohort as predictors.
Table I - Distribution of ABO blood groups in the three cohorts: female blood donors with children, female blood donors without children, and pregnant women. Cohort Donors with children
Material and methods
Three cohorts of women were consecutively enrolled in the period from January 2010 to September 2014: (i) cohort 1, female blood donors with one or more children; (ii) cohort 2, female blood donors without children; and (iii) cohort 3, pregnant women. In order to avoid a difference in ABO blood group distribution according to ethnicity, we considered only Caucasian women in this study. ABO blood group was determined for all subjects, whose age and gender were also recorded. Women with subsequent pregnancies during the study period were recorded only once. The distribution of the ABO blood groups in the three cohorts was reported and evaluated comparatively by means of Pearson's chi2 test, with six degrees of freedom (d.o.f.). Further comparisons were performed between each pair of the cohorts. All estimates were obtained using Stata 13.1 (StataCorp LP, College Station, TX, USA).
ABO blood group
Total Donors without children
Total Pregnant women
The null hypothesis of the same distribution in all cohorts was rejected (Pearson's chi2 [6 d.o.f. ]=13.73, p=0.033).
Blood Transfus 2015; 13; 521-3 DOI 10.2450/2015.0322-14 © SIMTI Servizi Srl
521 All rights reserved - For personal use only No other uses without permission
Mengoli C et al
A number of studies have analysed the relationship between ABO blood type and infertility with conflicting Table II - Age (in years) of the women in the three cohorts.
Donors, with children
Donors, without children
results. However, almost all focused on the parental or maternal-foetal interaction in the ABO system. To our knowledge, this is the first study to address this issue from another point of view, i.e. comparing ABO blood group distribution between pregnant women and (nonpregnant) female blood donors. We think that this is a more correct approach for verifying the hypothesis of the influence of ABO-driven haemostasis on fertility rather than the immunological effect of ABO incompatibility. In the present study, the prevalences of different ABO blood groups were modestly, but significantly different in the three cohorts analysed. Namely, group B was 2.17% more frequent in pregnant women and 2.04% more frequent in female blood donors with children than in female blood donors without children; the difference comparing pregnant women to the aggregate donors was 2.01%. It cannot be excluded that confounder variables played some role. Immigrants were not included this analysis, in order to avoid a potential bias due to ethnic background. Age was a possible source of interference, but the logistic analysis did not support this possibility. Only few studies are available in literature on this issue and their results are conflicting10-13. However, although there are methodological differences, some comparisons with previous studies can be made. For instance, in a study conducted in Pakistan on 587 mothers and 1,656 pregnancies, B-positive mothers were more successful in reproduction and had a low percentage of antenatal loss than mothers with other ABO groups10. Interestingly, a more recent study found that O blood group was associated with diminished ovarian reserve, an important predictor of female fertility, in a relationship that was independent of increasing age11.
due mainly to a lower prevalence of group B subjects among the blood donors without children, compared to the other cohorts. Of all binary comparisons, only that of cohort 2 (female blood donors without children) vs cohort 3 (pregnant women) was statistically significant (Pearson's chi2 [3 d.o.f.]=10.49, p=0.015). Combining all donors, and comparing them to pregnant women, the Pearson's chi2 (3 d.o.f.) was 8.85 (p=0.031). The prevalence of B group in the aggregate donors was 9.37%, similar to the 9.21% of cohort 2 alone (female blood donors without children). The age distribution in the three cohorts is summarised in Table II, and also plotted in Figure 1. The age spanned from 18 to 64 years in the donor cohort and from 13 to 47 years in the pregnant cohort. The mean age was rather uniform, but the standard deviation appeared to differ substantially, due to a bimodal distribution (not reported here) in cohort 2. This difference was confirmed by ANOVA (p