A total of 30291 patients admitted to Konya Dr Ali Kemal Belviranlı Gynaecology, Obstetrics and Children Hospital between September 2015-December 2017 for a period of 27 months were included in this retrospective study. Records of patients were reviewed retrospectively from laboratory and hospital information system digitally.

While analysing the records of patients retrospectively, only one blood group test result of a patient was included in this study. When patients had different or incompatible blood group results in records, these patients were excluded from study. Blood samples with haemolysis, clotted and insufficient were excluded from the study.

Ethical consideration: The study was approved by Review Board and Ethics Committee of Konya Necmettin Erbakan University Meram Faculty of Medicine (Ref No: 2018/1475).

Sample collection and processing: Blood samples were collected by antecubital veno-puncture into the Ethylene Diamine Tetra Acetic acid (EDTA) anticoagulant bottle and centrifuged at 4000 rpm for 10 minutes at room temperature for reverse grouping. ABO and Rh-blood group tests were performed by gel centrifugation method on fully automated immunohematology analyser (Autovue Innova, Ortho Clinical Diagnostics, USA). Forward reverse (cell and serum grouping) and forward (only cell grouping) cards were used in gel centrifugation method according to procedure described by Mujahid A and Dickert FL, and manufacturer’s instructions [13]. These cards have microtubes on each of the cards and there is buffered gel solution containing specific antibodies such as anti-A, anti-B, anti-A/B, anti-D and anti-C/D/E in microtubes. The agglutination occurs when erythrocyte antigens react with corresponding antibodies present in the gel solution or in the serum or plasma sample. The gel column acts as a filter that catches agglutinated erythrocytes as they pass through the gel column during the centrifugation of the card. The gel column separates agglutinated erythrocytes from non-agglutinated erythrocytes based on size. Positive result occurs when any agglutinated erythrocytes are captured at the top or along the gel column. Non-agglutinated erythrocytes reach the bottom of the microtube forming a pellet and yielding negative result.

Data analyses were performed by Statistical Package for the Social Sciences (SPSS version 20.0). Chi-Square test was used to compare distributions of ABO blood groups and Rh-factor across gender. Monte Carlo exact test was used to estimate exact significance as the data set is too large to compute exact significance. A probability value <0.05 (p<0.05) was considered to be statistically significant.

A total of 30291 patients were included in the present study. Patients were divided into two major groups according to age. There were 29548 (97.5%) women in the age group of 17-75 and they were admitted to gynaecology and obstetrics departments. The number of children in the age group of 0-16 was 743 (2.5%) and they were admitted to paediatrics departments. Out of 743 children, 466 (62.7%) were females and 277 (37.3%) were males. Out of 29548 women, 19635 (66.5%) were pregnant admitted to obstetrics departments and their age was ranged between 17-45 years (27.2±8.2 years).

A Rh-positive was the most common blood group among women and children with the rates of 37% and 35.4% respectively and followed by O Rh-positive (28.4%, 29.8%), B Rh-positive (16.1%, 16.9%) and AB Rh-positive (7.3%, 6.8%). AB Rh-negative had the lowest frequency as its rate was under 1%. Rh positivity was predominant with the rate of 89% while Rh negativity was 11% in both study groups [Table/Fig-1,2]. The proportional difference of distribution of blood groups A and B is significant (p<0.05) and there was a significant association between the distribution of A, B, O blood groups and Rh-factor in the age group of 17-75 (p<0.05) [Table/Fig-1].

Frequencies of ABO blood groups were identical among males and females among children. Rh negativity rate in males (12%) was a little higher than that of females (10.7%). The distribution of ABO blood groups according to gender and the difference between Rh negativity rates were not statistically significant (p>0.05) [Table/Fig-3].

Among pregnant, A Rh-positive (37%) was the most frequent and followed by O Rh-positive (28.8%), B Rh-positive (16.6%) and AB Rh-positive (7.5%). The proportional difference of distribution of blood groups A and B was statistically significant (p<0.05). The majority of pregnant had Rh positivity with the rate of 90% [Table/Fig-4].

This is the first report about the distribution of ABO and Rh-blood groups among children, women and pregnant population in central Anatolia, Konya, Turkey. This retrospective study was carried out in gynaecology, obstetrics and children hospital and gave a detailed information about frequencies of ABO and Rh-blood groups among children, women and pregnant population. A Rh-positive was the most common blood group among both women and children population with the rates of 37% and 35.4% respectively and followed by O Rh-positive (28.4%; 29.8%), B Rh-positive (16.1%; 16.9%) and AB Rh-positive (7.3%; 6.8%). In a study including neoanatal population born at a private hospital in İstanbul, Turkey, blood group frequencies were investigated and A Rh-positive (38.7%) was found to be the most common blood group followed by O Rh-positive (30.%), B Rh-positive (14.2%) and AB Rh-positive (6.6%) [11]. Balcı YI et al., from Denizli, Turkey reported the frequencies of the blood groups A, O, B, and AB as 42.6%, 33.3%, 16.8% and 7.4% respectively in a study conducted with male and female population [14]. These results were in line with the results of the present study. Authors think that findings obtained from the studies which analyse common blood groups in different populations were important for effective management of critical stock levels in transfusion centres and blood banks in a country.

A lot of studies detected that ABO and Rh-blood groups vary among different geographic regions, ethnic and socio-economic groups worldwide [1,2,4,11]. A population-based cross-sectional study including 3.8 million adults in China reported ABO and Rh-blood group distribution in different ethnic groups. Blood group A (30.5%) was determined as the most common phenotype and followed by O (30.4%), B (29.4%) and AB (9.7%) [15]. These findings were consistent with the present results. Unlike these findings, Odokuma et al., and Eru et al., carried out studies including university students in South and North central region of Nigeria and reported the predominance of blood group O with the rates of 57.2% and 52.5% respectively [16,17].

The ABO and Rh-blood group antigens are related to many fields of medicine and genetics as well as blood transfusion [11,18]. Some diseases are found to be associated with blood groups [11]. A study from Ethiopia reported the significant association between ABO blood groups and malaria infection as high rates of asymptomatic malaria parasitemia were detected in donors with O blood group [19].

Previous reports from different countries of the world emphasised predominance of O blood group among British, American, Malaysians and Saudi Arabian. A study from Nigeria reported that blood group O was the most common (57.2%) among blood donors as similar to other studies involving blood donors from Ethiopia (42.1%) and Uganda (50.3%) [2,8,19]. On the other hand, the most common blood group was found to be B (35.9%) and followed by O (30.9%), A (22.5%) and AB (10.5%) respectively in a retrospective study conducted by Chaurasia RK et al., from India [3]. Studies carried out in different parts of India by Gupta R et al., and Rajshree B and Joshi YR et al., revealed same results as Chaurasia RK et al., and reported B was the most frequent blood group (37%; 36.4%) and followed by O (26.3%; 31.7%), A (25.6%; 22.2%) and AB (11.1%; 9.4%) respectively [3,9,12]. Moreover, Rh-positivity among blood donors is documented as 91.7% in India, 92.8% in Ethiopia, 94.8% in Nigeria and >95% in Uganda [2,8,12,19]. These findings confirmed the trend of high prevalence of Rh positivity in African and Indian population. The rates of Rh positivity in Turkey were a little lower than these populations and ranged between 83.7%-88% [18,20-22]. The present results were similar to data reported from Turkey as Rh positivity rates were 89% in women and children and 90% in pregnant.

Rh incompatibility causes perinatal morbidity and mortality. Because of this, determination of ABO and Rh-blood groups in pregnant women is important [23]. The prevalence of Rh-negative pregnant women in the present study was 10%. This rate was higher than the rates obtained in previous studies done in India (4.2%) and Nigeria (4.5%) [23,24]. This might be attributed to the differences among ethnic and genetic characteristics of populations.

In a study from Istanbul province of Turkey, it was seen that the distribution of A, O, B, and AB blood groups were 43.4%, 33%, 15% and 8.5%, respectively [18]. A study from Kayseri, reported blood group A was the most frequent (44%) followed by O (30.3%), B (16.2%), and AB (6.5%). These rates were parallel with the rates detected in a study carried out in Yozgat city of Turkey [21,22]. In the present study, the frequencies of blood group A among women and children populations were 37% and 35.4%, respectively and a little lower than those obtained from these studies but the rates of other blood groups were similar to these studies. In contrast to these data, in Rize province which is located in Eastern Black Sea region of Turkey, the rate of blood group O (44.07%) and A (44.07%) was found to be significantly higher and blood groups B (9.2%) and AB (2.6%) were significantly lower than the rates found in other cities of Turkey [20]. These differences could be due to the fact that some cities like Rize are prone to immigration rather than emigration.

In the present study, AB Rh-negative had the lowest frequency among both women and children population with the rate of 0.9%. Similar prevalence for AB Rh-negative blood group is emphasised in studies carried out by Özkasap S et al., (0.4%) and Kader C et al., (0.8%) in Turkey [20,22]. Also, these findings were consonant with results obtained from studies performed among students in various regions of Nigeria [1,5,6,16,17]. This data is vital for blood banks and transfusion centres in order to detect and update their critical stock level for this rare blood group.

A study carried out by Apecu RO et al., from Uganda reported a significantly higher rate of Rh negativity among males than females [2]. Khan MN et al., detected statistically significant difference in ABO blood group prevalence between males and females and found blood group B was the most prevalent (37.4%) in males but blood group O (32.6%) was the most common in females [25]. However, in the present study, A Rh-positive was the most frequent blood group in both male and female children population and there was no statistically significant association between the distribution of ABO-Rh-blood groups and gender. This similar pattern was observed in previous reports and it was indicated that the distribution of ABO blood groups according to gender was not statistical significant [11,16,19]. Apecu RO et al., found that the distribution of blood groups according to age of blood donors was not statistically significant [2]. Contrary to this, the present results revealed that the proportional difference of distribution of blood groups A and B among women in the age group of 17-75 was significant (p<0.05).

There were differences between the present results and data reported from other countries worldwide. [2,3,15-17,19] These differences can be associated with ethnic and genetic factors of populations from different geographic regions of world. On the other hand, the present results indicate a similar trend of ABO and Rh-blood group profile compared to some studies carried out in Turkey [11,14,18,20-22] [Table/Fig-5].

The study was conducted within a specific population of women, children and pregnant and no males were included in the study. The results cannot be generalised to entire population of Konya. Even if the study was carried out at one centre as gynaecology, obstetrics and children hospital, a good number of patients attended to the study.

Authors think that further studies should be performed in other geographic regions of Turkey to obtain big data about frequencies of ABO and Rh-blood groups for Turkey. Knowledge of distribution of ABO and Rh-blood groups in a country is important for effective management of blood banks and transfusion centres. Also, this would help to provide suitable blood storage and to access to safe blood for people in need.