Endometriosis is a chronic gynaecological disorderwhich severely impacts the quality of life of affectedwomen (
Identifying risk factors, especially in the severe form
of endometriosis, can shorten the time between onset of
symptoms and diagnosis. Proposed risk factors include
low body mass index (BMI), family history or personal
history of endometriosis, and dysmenorrhea (
On the other hand, several studies have shown a
correlation between ABO and Rh blood groups with
infectious and noninfectious diseases. In addition,
the distribution of ABO and Rh blood groups varies
worldwide because of geographical and ethnic differences
A biological explanation for the correlation between
main blood groups and certain diseases has not been
stated. Genomic studies have shown that single variations
at the ABO locus and ABO blood groups were associated
with pro-inflammatory cytokine tumour necrosis
factor (TNF) receptor levels and adhesion molecules
such as intercellular adhesion molecule (ICAM) and E-
The aim of present study was to identify any association between ABO and Rh blood groups with endometriosis. Identification of an association between ABO and Rh blood groups with endometriosis could assist with diagnosis at the early stages of this disease in at- risk women.
In this case-control study, we assessed women who underwent
diagnostic laparoscopy secondary to unexplained
infertility or tubal ligation at Royan Institute and Arash
Women’s Hospital between 2013 and 2014. The Ethics
Committee of Royan Institute approved this study and
all study participants signed an informed consent form.
Inclusion criteria consisted of women with endometriosis
or normal pelvis according to laparoscopic findings.
Endometriosis was confirmed according to ASRM classification
based on the features of the lesions during laparoscopy
and pathology reports. A total of 433 women
were assigned to the endometriosis and control (women
without endometriosis and normal pelvis) groups. In the
endometriosis group, we determined the stage of endometriosis
according to ASRM classification (
ABO and Rh blood group typing were performed before laparoscopy at laboratories located in Royan Institute and Arash Women’s Hospital. A questionnaire was completed for each woman.
Statistical analysis was performed by using the Statistical Package for the Social Sciences (SPSS) version 20. The chi-square, t test, one-way ANOVA, and logistic regression tests were used for data analysis. Ordinal logistic regression was used to examine the relationship between the ABO and Rh blood groups to stages of endometriosis. Data are presented as number (percent) or mean ± SD. P<0.05 were considered significant.
In this study there were 433 participants. According to laparoscopy findings, 213 women with endometriosis were placed in the endometriosis group and 220 subjects with normal pelvis comprised the control group.
The 433 enrolled women had a mean age of 30.74 ± 5.97 years. The mean age of the endometriosis groups was 30.43 ± 5.81 years and the control group was 31.05 ± 6.11 years, which was not statistically significant [P=0.27, odds ratio (OR): 0.98, 95% confidence interval (CI): 0.95-1.01].
The average BMI in the endometriosis group was 23.48 ± 3.38 kg/m2. The BMI of the control group was 25.88 ± 4.40 kg/m2. Statistical analysis showed a significant inverse association between BMI and endometriosis (P<0.001, OR: 0.85, 95% CI: 0.80-0.90). The OR indicated that each unit increase in BMI decreased the risk of endometriosis.
In this study, the most common ABO blood group
was O with a frequency of 40.6%. There was no significant
association between ABO blood groups and
endometriosis (P=0.091), although the risk of endometriosis
in the O blood group was lower than the other
blood groups. The Rh+ blood group was present in 390
women (90.1%). There was no significant correlation
between Rh blood group and risk of endometriosis
Among demographic variables, regression analysis
indicated that a positive family history of endometriosis
in first-degree relatives had a significant association
with the risk of endometriosis (P=0.004, OR:
8.85, 95% CI: 2.01-38.98). The risk of endometriosis
in women whom first-degree relatives (mother, sister)
suffered from endometriosis was approximately
9 times more than women without a positive family
In this study, the most common symptoms of endometriosis
were pain during menstruation (73.7%) and
infertility (56.3%). There was no significant association
between the different stages of endometriosis (I-IV) and
frequency of ABO and Rh blood groups (
One-way ANOVA was used to compare mean age and
BMI of women in different stages of endometriosis.
Mean age and BMI did not significantly differ in the
different stages of endometriosis (
The frequency of ABO and Rh blood groups in the endometriosis and control groups
|Blood groups||Endometriosis groupn (%)||Control groupn (%)||OR (95% CI)||P value|
|A||73 (34.3)||73 (33.2)||1.316 (0.84-2.04)||0.091|
|B||50 (23.5)||40 (18.2)||1.645 (0.98-2.74)|
|AB||14 (6.5)||7 (3.2)||2.63 (1.01-6.83)|
|O||76 (35.7)||100 (45.4)||Reference level|
|Rh+||190 (89.2)||200 (90.9)||Reference level||0.55|
|Rh-||23 (10.8)||20 (9.1)||1.21 (0.64-2.27)|
OR; Odds ratio and CI; Confidence interval.
Relation between history of endometriosis in first-degree relatives with the risk of endometriosis
|Family history of endometriosis||Endometriosis groupn (%)||Control groupn (%)||OR (95% CI)||P value|
|No||197 (92.5)||218 (99.1)||Reference level||0.004|
|Yes||16 (7.5)||2 (0.9)||8.85 (2.01-38.98)|
OR; Odds ratio and CI; Confidence interval.
Association of severity of endometriosis with ABO and Rh blood groups
|Blood group||Control groupn=220||Endometriosis groupn=213||P valuec||P valueb||OR (95% CI)a|
|Stage 1||Stage 2||Stage 3||Stage 4|
|A||73 (33.2)||6 (27.3)||7 (30.4)||27 (36.5)||33 (35.1)||0.053||---||Reference level|
|B||40 (18.2)||4 (18.2)||2 (8.7)||19 (25.7)||25 (26.6)||0.292||1.297 (0.799-2.106)|
|AB||7 (3.2)||3 (13.6)||3 (13)||1 (1.4)||7 (7.4)||0.310||1.542 (0.668-3.557)|
|O||100 (45.4)||9 (40.9)||11 (47.8)||27 (36.5)||29 (30.9)||0.127||0.723 (0.477-1.096)|
|Rh+||200 (90.9)||20 (90.9)||20 (87)||65 (87.8)||85 (90.4)||0.871||---||Reference level|
|Rh-||20 (9.1)||2 (9.1)||3 (13)||9 (12.2)||9 (9.6)||0.680||1.130 (0.630-2.031)|
Values are given as number (%). a; Results are reported based on the odds ratio (OR) obtained from ordinal logistic regression, b; P value based on ordinal logistic regression, and c; P value based on Fisher’s exact test.
The frequency of different stages of endometriosis, age, and body mass index (BMI) in the endometriosis group
|Stage of endometriosis||n (%)||Age (Y) Mean ± SD||BMI (kg/m2)Mean ± SD|
|Stage 1||22 (10.3)||31.59 ± 4.53||23.65 ± 3.38|
|Stage 2||23 (10.8)||29.83 ± 4.98||23.72 ± 2.78|
|Stage 3||74 (34.8)||30.64 ± 5.89||23.17 ± 3.61|
|Stage 4||94 (44.1)||30.14 ± 6.22||23.62 ± 3.36|
|Total||213 (100)||30.43 ± 5.81||23.48 ± 3.38|
|P value -||0.696||0.812|
Several studies have shown that the distribution of
Rh and ABO blood groups can depend on ethnicity and
change in a geographic area over time (
Although the result of our study showed that the risk of
endometriosis in women with blood group O was lower
than other ABO blood groups, this difference was not statistically
significant. The risk of endometriosis in all ABO
blood groups was similar, which was consistent with studies
by Daliri et al. (
In the present study, the most frequent Rh blood group
was Rh+. There was no significant relationship observed
between Rh and the risk of endometriosis, which was
consistent with another study in Iran by Daliri et al. (
The results of our study showed that the different
stages of endometriosis and ABO and Rh blood groups
did not have a significant relationship, which was consistent
with findings by Demir et al. (
The limitations of this study included difficulties in finding women with normal pelvis during laparoscopy and low sample size based on the study power of 0.56. The power of this study indicated the need to conduct a study with a larger sample size.
This study has shown no significant association between the main blood groups (ABO and Rh) and the risk of endometriosis. It seems that Iranian women with the O blood group are less likely to develop endometriosis compared to women with other blood groups. However, this finding should be confirmed with a larger study population. In addition, the severity of endometriosis was not correlated to any of these blood groups.