In December 2019, severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) was detected in Wuhan, Hubei Province, China (1), and the disease was later named coronavirus disease (COVID-19) (2). Over the past 3 years, the novel coronavirus infection has spread around the world, causing a worldwide pandemic (3, 4). The severity of the disease ranges from mild asymptomatic infection to atypical pneumonia, acute respiratory distress syndrome, and multiple visceral failure (5), with high morbidity and mortality.

Large-scale studies have been reported on the impact of COVID-19 on the general population, but research and data on this group of pregnant women are still limited. Due to a variety of physiological changes during pregnancy, respiratory, circulatory, and immune system changes (6, 7), making pregnant women susceptible to various pathogens and prone to severe disease (8), during the epidemic, they are at high risk of contracting the new coronavirus (9). With the continuous understanding of the disease, infection with the novel coronavirus during pregnancy will have different degrees of impact on pregnant women and fetuses, affecting pregnancy outcomes (10–13).

Since the emergence of the pandemic, SARS-CoV-2 has been mutating constantly, with many variants emerging globally (14). There are five SARS-CoV-2 variants identified by the World Health Organization: Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2) and Omicron (B.1.1.529). Many mutations in variants, such as Delta and Alpha (15), are associated with immune evasion and higher infectivity, and there is uncertainty about the mutations in Omicron at this surface, and many mutations in the S protein of the Omicron variant may help the virus evade infection antibodies and other immune responses (16). The large number of mutations in Omicron increases the ability of the virus to enter cells and a higher risk of transmission (15, 16). Since 2022, Omicron has been circulating in China as the main variant (17), with a strong transmissibility with the adjustment of domestic epidemic prevention policies and the increasing number of infections. Some data from non-pregnant patients infected with Omicron have shown that it causes milder disease than those caused by previous variant infection (18, 19), and in clinical observations, pregnant patients have a similar situation, and with the general increase in awareness of the new coronavirus, 84.80% of people have received COVID-19 booster vaccination by June 2021 under the publicity and guidance of the Chinese government (20), studies have shown that COVID-19 vaccination has a promising effect on the prevention of SARS-CoV-2 infection, hospitalization, and ICU admission during pregnancy, with a reduction in preterm birth, and no increase in maternal comorbidities and complications, as well as adverse maternal and neonatal outcomes (21).

There are still many unknowns about the impact of the Omicron variant on pregnant women and newborns (22), and research reports are limited. This study summarizes the clinical data, maternal and infant data of pregnant women infected with the novel coronavirus variant admitted to our hospital and analyzes the clinical characteristics and pregnancy outcomes of patients, to provide reference for clinical treatment.

This study showed that infection with the COVID-19 variant during pregnancy has a shorter incubation period, and the most common symptoms are fever, sore throat, nasal congestion, runny nose, cough and other flu-like symptoms. Most of these patients had fever (9 4.38%) and sore throat (59.55%), which were like the early epidemic among the Wuhan pregnancy cases reported by Chen et al. The most common symptoms were fever (75%) and cough (73%), 9 to 5 percent of patients showed similar results (23), except for fever The chance of symptoms is higher, unlike the 6 to 2.7% of pregnant women reported by Rasha Khoury et al. in the United States to be asymptomatic before or during hospitalization (24). Physiological changes in the respiratory, circulatory, and immune systems occur during pregnancy due to hormonal changes (8, 9), increasing the risk of respiratory virus infection during pregnancy and more serious clinical manifestations after infection (25). As the virus continues to mutate, virus virulence and pathogenicity change, and the Omicron variant decreases in its virulence and pathogenicity in causing lung infection or ARDS (26–28), clinical manifestations and characteristics also have different manifestations. Another reason for the reduction in clinical symptoms and the reduction in critical cases may be related to the high vaccination rate, with more than 90 percent of patients receiving more than two doses of vaccine before pregnancy, and like recent studies, vaccination has a high efficacy in preventing SARS-CoV-2 infection, hospitalization, and intensive care unit admission during pregnancy, and reducing preterm birth (20).

Compared with no infection, infection with the novel coronavirus during pregnancy was associated with a faster fetal heart rate, fetal intrauterine distress, increased occurrence of cloudy amniotic fluid, and an increased incidence of cesarean section (4 to 4.9%), but there was no difference in preterm birth rates. Previous studies have observed an increase in cesarean section rates in COVID-19-positive pregnant women (29–31), primarily due to clinical manifestations of severe disease following infection or exacerbations due to underlying medical conditions, pregnant women undergo cesarean section due to worsening respiratory symptoms (32, 33), and an increased rate of preterm birth may occur (34, 35). In our study, patients who did not have novel coronavirus pneumonia or who required respiratory support or were admitted to the ICU ward were classified according to the severity of symptoms (36). The patients enrolled in the study were mild and asymptomatic infections, with obvious symptoms and mild disease, which were consistent with the pathogenic characteristics of the variant Omicron (26–28) Infection with this variant is associated with a lower likelihood of severe illness in pregnant women (37, 38). This study showed that the indications for cesarean section are mainly fetal intrauterine distress, repeated high fever after infection with the virus, increased fetal heart rate, easy to be complicated by significantly increased fetal heart rate, and fetal intrauterine distress. However, after reasonable symptomatic treatment and other treatment, the symptoms were relieved, the condition did not worsen, and there was no difference in the rate of premature birth of patients.

From the results of laboratory tests, the lymphocyte counts of 8 8.76% of patients in the positive group is reduced, and it is also observed in the subgroup analysis of the underlying disease that the lymphocyte count of infected with the new coronavirus in the state of the underlying disease is lower than that of those without the underlying disease. Chen L et al. reported that lymphopenia was observed in 44% of pregnant women and COVID-19 clinical features (23); Guan WJ et al. reported that 83.2% of nonpregnant patients had lymphopenia, and severe patients were more obvious (39). Research by Lee J. et al. suggests that lymphopenia and its severity can be a reliable predictor of clinical outcome for COVID-19, with lower lymphocyte counts predicting more severe disease and increased need for therapeutic intervention (40). Whether lymphopenia is a predictor of COVID-19 in pregnancy requires further research and more data.

Hypercoagulable status during pregnancy is determined by increased prothrombotic factors (VII, VIII, X, XII, v-W factor F) and fibrinogen, decreased S protein and fibrinolysis, and detection of coagulation function Changes, fibrinogen and D-dimer increase, and APTT shortens (41, 42). The laboratory results of this study showed that the positive group had prolonged APTT and PT, and decreased fibrinogen and platelet counts, which were different compared with the negative group. The study of Pluta J. et al. showed that the most commonly observed changes in the coagulation system caused by COVID-19 were D-dimer, elevated fibrinogen, prolonged clotting time, no severe thrombocytopenia, and coagulation abnormalities DIC (disseminated intravascular coagulation) and SIC (coagulopathy due to sepsis) diagnostic criteria, described as COVID-19-related coagulopathy (43). COVID-19 variant infection has an impact on coagulation function, but they are all within the normal range, there is no difference in the risk of postpartum hemorrhage, and there is a risk of promoting thrombosis.

In this study, there was no anticoagulation during pregnancy and postpartum, and no thrombotic events occurred in either group. Thrombotic complications in patients with COVID-19 are pulmonary microvascular thrombosis (immunothrombosis) (44) or deep vein thrombosis (45). Changes in thrombotic and fibrinolytic may persist up to 3 months postpartum and then return to pre-pregnancy status (46, 47). Studies have not shown an increased incidence of VTE or immunothrombosis in patients with COVID-19, and no VTE events have been reported during treatment with prophylactic and therapeutic unfractionated heparin (UFH) or LMWH, Physical methods during pregnancy and postpartum and appropriate postpartum activity are important methods for preventing blood clots, and more clinical research is needed for routine medical prophylaxis. Given the risks, prophylactic anticoagulation in pregnant women with C covid-19 infection remains uncertain.

The most common cause of neonatal admission to NICU is respiratory distress, and risk factors for neonatal respiratory distress include prematurity, cloudy amniotic fluid, maternal diabetic chorioamnionitis, oligohydramnios, or structural lung abnormalities (48). In this study, the incidence of amniotic fluid opacity increased in the positive group, but there was no increase in complications such as neonatal respiratory distress, and there was no difference in NICU occupancy. Considering respiratory contagiousness, newborns were transferred to a neonatal isolation area for unified nursing care after birth, and COVID-19 PCR was tested daily by nasopharyngeal swab for two consecutive days to rule out vertical transmission or close horizontal transmission from the mother after delivery. No positive results for vertical transmission were observed. Previous studies have described positive rates of 2 to 4.4 percent of neonatal COVID-19 PCR tests at delivery (29, 49–51), but vary widely, PCR tests of COVID-19 such as amniotic fluid, cord blood, placenta, and breast milk have found no evidence of vertical transmission (52–54), and further research is needed.

Dicategorical univariate logistic regression analysis was used to screen for factors at risk of C-19 infection in pregnancy, and the susceptibility of both groups to COVID-19 infection. There was no difference, and pregnancy did not increase the risk of COVID-19. However, after infection with the virus, the incidence of cesarean section in patients with gestational diabetes increased by 4.01 times. Consistent with the findings of Helmut J. Kleinwechter et al. women with gestational diabetes have an increased risk of susceptibility to COVID-19 and severe disease, and adverse maternal outcomes are more common (55). Previous studies have also suggested that patients with underlying medical conditions (eg, hypertension, diabetes, obesity) are not only associated with disease severity, but also increase perinatal adverse outcomes (56, 57).

This study showed that most patients infected with the Omicron variant during pregnancy developed symptoms, and the rate of severe and critical cases decreased significantly. Viral infection can affect the coagulation system, and lymphopenia and severity may be related to disease and prognosis; Compared with the non-viral group, viral infections increased cesarean section rates, but there was no difference in the incidence of preterm birth, particularly in pregnant women with gestational diabetes, where infection led to a fourfold increase in the incidence of cesarean section. There was no difference in neonatal complications, there was no evidence of vertical infection, and separate care for mother and infant may help reduce the risk of neonatal infection.

The shortcomings of this study are that the admission cases are single-center data of the unit, and the inclusion of more data from other medical centers in the region or even in the region helps to reflect the conclusions more realistically, especially the conclusion that infection in gestational diabetes patients increases the incidence of cesarean section; Data on the symptoms and prognosis of the long coronavirus after infection during pregnancy are limited and longer follow-up is required.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

The studies involving humans were approved by this study was reviewed and approved by the Medical Ethics Committee of Guangdong Maternal and Child Health Care Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

HX: Conceived the original idea, Provides data collection and data analysis, Writing—original draft. CC: Provides data collection and data analysis, Writing—original draft. SH: Contributed tables to the manuscript, Writing—review & editing. WZ: Contributed tables to the manuscript, Writing—review & editing. SC: Conceived the original idea, Writing—review & editing. XH: Contributed tables to the manuscript, Writing—review & editing. YLu: Conceived and designed this study, Writing—original draft. YLi: Conceived and designed this study, Writing—original draft. All authors contributed to the article and approved the submitted version.