ABO blood group and COVID-19 in pregnant women: A case-control study.

In some countries, coronavirus disease 2019 (COVID‐19) is the leading cause of death in pregnant women. The risk factors for severe COVID‐19 are similar to those identified for the general population. The effects of ABO blood groups and COVID‐19 are unclear. Among pregnant women, this association has been identified in the United Kingdom, with women with blood group A showing a higher risk of developing COVID‐19.

A retrospective case–control study was performed. The population included all pregnant women who attended the emergency department for respiratory symptoms (suspected cases of COVID‐19) at a single center between May 14, 2020, and October 9, 2021. The cases were pregnant women with positive polymerase chain reaction results for severe acute respiratory syndrome coronavirus (SARS‐CoV‐2) (designated COVID‐19+), and controls were women with negative polymerase chain reaction results for SARS‐CoV‐2 (designated COVID‐19–) in a 1:1 ratio. The blood group was determined by the column agglutination method. Pearson χ2 test was used to analyze the association between the blood group and the probability of having COVID‐19.

Two hundred patients who met the selection criteria were included. The Table 1 shows the characteristics of both groups of patients. The blood group did not influence susceptibility to COVID‐19 (P = 0.754). A difference was observed in age and susceptibility to COVID‐19 (P = 0.034). The mortality rate was higher in the COVID‐19+ group than in the COVID‐19– group (4% vs. 0%, respectively; P = 0.043), but the blood group did not influence mortality (P = 0.059). COVID‐19 was a risk factor for maternal mortality (odds ratio [OR], 2.04; 95% confidence interval [CI], 1.77–2.35). In pregnant women with COVID‐19, the infection had a median of 29 gestational weeks. Moderate–severe COVID‐19 was observed in 74 (74%) patients and occurred mainly in the third trimester (44 of 74). No differences were observed between the ABO blood group and disease severity (P = 0.965).

TABLE 1

Characteristics of pregnant women by study group (COVID‐19+ and COVID‐19−), n = 200

Characteristics	All	COVID‐19+	COVID‐19−	P value
	N = 200	n = 100	n = 100
Age group, year
≤29	47.5% (95)	55.0% (55)	40% (40)	0.034
>30	52.5% (105)	45.0% (45)	60% (60)
Blood group
A	20.5% (41)	21% (21)	20% (20)	0.754
B	4.5% (9)	5% (5)	4% (4)
AB	0.5% (1)	1% (1)	0% (0)
O	74.5% (149)	73% (73)	76% (76)
Patient group
A	21% (42)	22% (22)	20% (20)	0.298
No A	79% (158)	78% (78)	80% (80)
B	5% (10)	6% (6)	4% (4)	0.643
No B	95% (190)	94% (94)	96% (96)
O	74.5% (149)	73% (73)	76% (76)	0.237
No O	25.5% (51)	27% (27)	24% (24)
Rhesus factor
Positive	98.5% (197)	98% (98)	99% (99)	0.803
Negative	1.5% (3)	2% (2)	1% (1)
Outcome at the end of pregnancy
Live	98% (196)	96% (96)	100% (100)	0.043
Deceased	2% (4)	4% (4)	0% (0)
Obstetric outcome
Term birth	57.0% (114)	64% (64)	50% (50)
Preterm birth	14.5% (29)	29% (29)	0% (0)	<0.001
Second‐trimester abortion	0.5% (1)	0% (0)	1% (1)
First‐trimester abortion	28.0% (56)	7% (7)	49% (49)

Abbreviation: COVID‐19, coronavirus disease 2019.

The four pregnant women who died had blood group O, three patients who died had a history of obesity, and three had advanced maternal ages (older than 35 years). The frequencies of the blood groups depend on the geographical regions. In Turkey, a country with a high prevalence of blood group A, this blood group increased the susceptibility to COVID‐19 (OR, 2.1; 95% CI, 1.5–2.9). Pregnant asymptomatic women were not included. However, it has been described that up to two‐thirds of pregnant women with COVID‐19 are asymptomatic.

This study found no association between blood group and COVID‐19 susceptibility, severity, or death in pregnant women. Similar to other research, two risk factors were identified in pregnant women with COVID‐19: age and obesity.

AUTHORS CONTRIBUTIONS

The authors assume responsibility for conducting the trial and ensuring data integrity, analysis, and protocol adherence. C.G.T.A.: designed the protocol and drafted the original manuscript. O.D.C.G. and C.S.L: acquisition of data. C.S.L.: preparation of Tables. C.G.T.A.: analysis or interpretation of data. R.M.A.: substantively revised the manuscript. All authors contributed to the critical review of the paper and approved the final version of the manuscript.

FUNDING INFORMATION

The authors received no specific funding for this work.

CONFLICT OF INTEREST

The authors have no conflicts of interest.