Identifying the Risk Factors of Adverse Pregnancy Outcomes among Women with COVID-19: A Population-Based Case-Control Study in Southern Iran

Introduction: Pregnant women and their fetuses are considered as high-risk groups during the COVID-19 pandemic. The aim of this study was to identify the risk factors of adverse pregnancy outcomes among women with COVID-19. Methods: This case-control study was conducted among pregnant women who delivered live infants at least 60 days before data collection in Hormozgan Province, south of Iran, 2021. The case and control groups included women with and without the history of COVID-19, respectively. A 47-item checklist including demographic information of the mothers, maternal current and past medical history, maternal and fetal prenatal and post-natal outcomes; and other COVID-19 related outcomes was used. The logistic regression analysis was used for data analysis. Results: A total of 1337 women (668 in case and 669 in control groups) participated in this study. The mean (SD) gestational age in the case and control groups were 32.83 (84.64) and 23.75 (6.93) weeks respectively. Maternal age and the incidence of abortion, obesity, and multiple pregnancies was higher in the COVID-19 group compared with the control group. The most common COVID-19 symptoms were myalgia (24.8%), cough (19.3%), fever (17.5%) and olfactory disorder (14.3%). The preventive factors against COVID-19 adverse pregnancy outcomes were low and normal body mass index, influenza vaccination history, and multivitamin consumption, while the risk factors were multiple pregnancies, abortion and preterm labor. Conclusion: This study showed that pregnant women were to COVID-19. The identified risk factors for COVID-19 adverse pregnancy outcomes can be used to prioritized pregnant women in receiving COVID-19 related health services.

these symptoms may not be seen in infants.COVID-19 symptoms in newborns may include low grade fever, and body temperature instability, which frequently occurs in premature neonates.Infants might present with symptoms including malnutrition, lethargy, vomiting, diarrhea, and bloating. 8In general, limited studies have been conducted on the effects of COVID-19 during and after pregnancy on mothers and newborns and the findings of these studies were contradictory. 9For instance, a study by Banaei et al reported that COVID-19 was associated with adverse maternal outcomes, including fetal distress, preterm delivery, respiratory distress, thrombocytopenia with abnormal liver function, death, decreased fetal movement, intrauterine distress, anemia, hemorrhage, severe postpartum dyspnea, premature rupture of membranes, preterm delivery with meconium-stained amniotic fluid, and neonatal outcomes, including low birth weight, low Appearance, Pulse, Grimace, Activity, and Respiration )APGAR( score, and neonatal death. 102][13] The limitations of the previous studies may be listed as follows: (1) very small sample size, (2) lack of control group, and (3) lack of population-based studies.Therefore, there is a need for large population-based studies among pregnant women and newborns to identify the outcomes and risk factors for adverse pregnancy outcomes in COVID-19 patients.The findings of such studies will be helpful in designing strategies to maintain and promote maternal and neonatal health during COVID-19 pandemic. 14The result of this study can also help health care professionals design health interventions to improve maternal and neonatal health during the COVID-19 pandemic.Therefore, the aim of this study was to investigate maternal and neonatal outcomes of COVID-19 in pregnancy in Southern Iran.

Study Design and Data Collection
This study was a retrospective case-control study that was conducted in Hormozgan province, south of Iran in 2021.Equal number of cases and controls were enrolled in this study (n = 910).Confirmation of the COVID-19 was based on the polymerase chain reaction (PCR) examination of nasopharyngeal swab along with chest computerized tomography (CT) scan.All pregnant mothers in Hormozgan province were included in the study from the beginning of the COVID-19 pandemic (4 November 2020) until October 2020.

Sampling Method and Study Population
The study population included all mothers with a history of COVID-19 (case group) and mothers without a history of COVID-19 (control group) who delivered to live infant at least 60 days from data collection.According to the Integrated Health System (SIB) database, 16139 pregnant mothers gave birth to live infants from 4 November 2020 to October 2020 in Iran, among which, 910 (5.5%) mothers with COVID-19 were from the Hormozgan province, Iran.As the number of the study population was equal to the sample size for the case group, data collection was performed using census sampling (All pregnant mothers with COVID-19 from the beginning of the epidemic to October 2020).Sampling in the control group was performed based on stratified random sampling method, where cities of the province were considered as classes.
As individual matching was not possible to match cases and controls in terms of maternal age and gestational age at delivery, group matching was performed in this study.Other than the main characteristics used for matching, it was attempted to homogenize groups based on the three important items in case-control studies, including selection, comparability, and exposure.In terms of "comparability", group matching as well as suitable statistical methods (comparison between the two groups and regression analysis) were used to reduce bias.
The main purpose of the study was explained to the participants orally.Subjects were asked to read and sign the informed consent form.Participants were assured that their information will be confidential.Participants were asked to complete the research questionnaires in a separate environment.After completing the questionnaires, the contact information of the researchers was provided to the participants if they wished to be notified of the findings of the study.

Outcome Measurements
A 47-item checklist including demographic information, influencing factors, maternal and fetal prenatal and postnatal outcomes; and other maternal and fetal outcomes due to COVID-19 was used to measure the study outcomes based on literature and library studies.The checklist validity was approved by an expert group (10 faculty members of obstetrics and gynecology).Sampling was conducted in the comprehensive urban and rural health centers in the cities of the Hormozgan province.The SIB integrated health system was used for data extraction.In order to standardize data collection procedure, necessary training was provided to enumerators regarding the proper way of completing the questionnaires.The maternal and pregnancy characteristics of the participants depicts in Table 1.Both groups were not significantly different in terms of location, level of education of the mother or her spouse; mother or her souse's occupation; and income level (P > 0.05).There was a significant difference in terms of age, gravida, number of abortions, and number of live children between case and control groups (P < 0.05).All these variables were significantly higher among the case group compared to the control group.Gestational age at birth was significantly lower among the case group compared to the control group (P = 0.02).Prevalence of influenza vaccination was significantly higher among the control group (54.1%) compared to the case group (54.1% vs 44.6%, respectively, P = 0.001).

Primary and Secondary Outcomes
The rate of multiple pregnancy was significantly higher among the case group compared to the control group (4.2% vs 0.6%, respectively, P < 0.001).Furthermore, the prevalence of overweight/obesity was significantly higher among case group compared to the control group (40% vs 30%, P = 0.003).In the case group, 4.2% of the women did not take multivitamins, which was significantly higher compared to the control group (1.9%, P = 0.01).Time of multivitamin initiation was not statistically different between the case and control groups (P = 0.83).
Table 2 shows the comparison of pregnancy and childbirth outcomes between the case and control groups.There was a statistically significant difference between the case and control groups in terms of mode of delivery; so that the rate of cesarean section was significantly higher in the case group compared to the control group (40.7% vs 34.1%, respectively, P = 0.002).According to the standard mental health screening tool, there was no statistically significant difference in the levels of anxiety, stress, and other mental disorders between case and control groups (P > 0.05).The rate of abortion in the case group was significantly higher than the rate of abortion in the control group (1.8% vs 0.4%, P = 0.02).The rate of preterm labor was significantly higher in the case group compared to the control group (11.7% vs 5.9%, respectively, P < 0.001).
Ninety-six percent of the infants were apparently healthy at birth.Skin-to-skin contact was initiated immediately after birth and breastfeeding was initiated within four hours after birth in 89.2% of infants born to mother with COVID-19.There was a statistically significant difference in terms of skin-to-skin contact with mother and birth weight between the case and control groups (P < 0.001).The rate of artificial feeding was significantly higher in case group compared to the control group (4.1% vs 1.7%, respectively, P = 0.006).Furthermore, there was a significant difference in the distribution pattern of neonatal conditions between the case and control groups.While the incidence of intrauterine growth restriction (IUGR), congenital, and other neonates, was 4 (0.6%), 4 (0.6%), and 4 (0.6%), respectively, no such conditions were reported among the control group (P < 0.001) (Table 3).
Multivariate logistic regression analysis was performed to identify the factor that were associated with COVID-19 by including variables with significant difference between case and control groups in the model.In this model, the Hosmer and Lemeshow test was not significant (P = 0.35), which indicates that the test was appropriate for the data.
Based on the regression analysis, low body mass index (OR = 0.56, P = 0.02), normal body mass index (OR = 0.64, P = 0.03), history of influenza vaccination in the past year (OR = 1.45,P = 0.002), multiple pregnancies (OR = 0.13, P = 0.01), were significantly associated with COVID-19.It meant that women with low and normal body mass index were 0.44% and 0.36%, respectively less likely to develop COVID-19 compared to women with high body mass index.Women who had not been vaccinated against influenza in the past year were 0.45% more likely to develop COVID-19 compared to women who had been vaccinated against influenza.Women who did not have multiple pregnancies had a 0.86% lower chance of developing COVID-19 compared to those who had multiple pregnancies (Table 4).

Discussion
The results of the present study showed that pregnant women with COVID-19 were older and had higher incidence of abortions, obesity, and multiple pregnancies compared to the control group.However, there was no statistically significant difference between the history of smoking and alcohol between case and control groups.Some studies have reported that pregnant women with COVID-19 were more likely to be older, obese, have twin pregnancies, and have a history of high blood pressure compared to non-infected women.The study also indicated that alcohol use and smoking were less common among women with COVID-19, especially among primiparous women, compared to non-infected women. 15t can be suggested that high-risk pregnancies, including twin pregnancies, make pregnant women more exposed to COVID-19 due to more frequent visits to medical centers that results in increased exposure to COVID-19.The present study showed that higher body mass index of pregnant women was associated with increased risk of developing COVID-19.In a study conducted by Gao et al. a significant and positive relationship was reported between BMI and ICU admission due to COVID-19, and hospital admission or death due to COVID-19, which were in line with the findings of the present study. 16Complications of obesity can be attributed to the presence of excess fat deposition in tissues, including liver, heart, or skeletal muscle, which results in metabolic dysfunction and insulin resistance.Type 2 diabetes, high blood pressure, cardiovascular disease and drug abuse can increase the risk of developing COVID-19 in obese women. 17he present study showed that pregnant women who were vaccinated against influenza had a lower risk of developing COVID-19 compared to unvaccinated women.A cohort study conducted by Candelli et al showed that influenza vaccination could be effective in reducing the risk for coronary heart disease and mortality, which was in line with the observed protective role of influenza vaccination against COVID-19 in the present study. 18It is hypothesized that influenza vaccination may reduce the risk of other infectious diseases including COVID-19 due to pathophysiological mechanisms, including structural similarities in cell receptor ligands and antibody-reciprocal reaction and non-specific cell-response between influenza and COVID-19. 19,20he present study also showed that the use of multivitamins during pregnancy could reduce the incidence of COVID-19.Some vitamin deficiencies, including vitamin D, can increase the risk of developing COVID-19.Pregnant women can be more at risk for vitamin deficiency compared to non-pregnant women.The increased risk of vitamin D deficiency in pregnant women might be related to pregnancy, area of living, and limited sunlight exposure due to lockdown in COVID-19 pandemic.Proper intake of vitamin D supplements was previously reported to reduce the risk of viral respiratory infections. 21Vitamin D may affect body response to COVID-19 is two ways.First, vitamin D increases the production of antimicrobial peptides in the respiratory epithelium, reduces the rate of virus replication, viral infection, and symptoms.Second, vitamin D reduces the inflammatory response to SARS CoV-2 by increasing the concentration of anti-inflammatory cytokines and decreasing the concentration of proinflammatory cytokines that increase lung damage. 22 systematic review conducted in 2021 showed that the COVID-19 can cause abortion and fetal loss through inflammation and placental insufficiency.In addition to placental inflammation, fibrin deposition and multiple villi infarcts in the placenta of mothers infected with SARS-CoV-2 can impair the transfer of nutrients from mother to fetus and lead to adverse pregnancy outcomes. 23Due to the pandemic conditions, women had limited access to reproductive health services; therefore, unplanned pregnancies may have occurred during this period.On the other hand, women had limited access to reproductive health services during pregnancy and the risk of abortion and the negative pregnancy outcomes could increase.Some studies have shown that black or Hispanic pregnant women had a higher rate of COVID-19 and hospitalization compared to pregnant women of other races and ethnicities. 24,25This may reinforce the hypothesis that race and ethnicity may influence the course of the disease in COVID-19.However, the present study found no statistically significant difference in skin color between affected and non-affected women.In general, differences between the findings of the present study and the previous studies may be due to differences in the course of the disease, symptoms and severity of the disease, or differences in the immune systems of mothers and fetuses.The immune system response in pregnancy is complex and varies based on gestational age, immune response, duration and severity of infection; and maternal and neonatal outcomes of COVID-19.
A systematic review and meta-analysis compared COVID-19 symptoms between pregnant and nonpregnant women.The study reported that the most common COVID-19 symptom in both pregnant and non-pregnant women were cough (pregnant: 48.5%; nonpregnant: 53.5%) followed by fever (pregnant: 75.5%; non-pregnant: 74%) and myalgia (26.5%). 26This finding was in line with the findings of the present study, which reported that the most common symptoms in pregnant women with COVID-19 was fever, myalgia, and cough.In the study by Luo Q-Q et al. the most common symptoms were fever, cough and myalgia, respectively. 27mith et al. showed that the incidence of preterm delivery, cesarean section, low birth weight, and neonatal intensive care unit (NICU) admission was higher among pregnant women with COVID-19 compared to the normal population, which was in line with the findings of the present study. 28One of the mechanisms for increased incidence of preterm delivery in pregnant women with COVID-19 can be pre-placental hypoxia that can occur as a result of maternal respiratory disorders due to pneumonitis.This can promote a combination of antiangiogenic and pro-inflammatory factors that cause endothelial dysfunction, end organ damage, and placenta insufficiency, and lead to partial fetal hypoxemia and finally, fetal hypoxia. 29Viral infection during pregnancy can stimulate an abnormal response to opportunistic bacterial infections that may lead to preterm delivery. 30ome studies reported that a large number of patients with COVID-19 experienced preterm labor, but the validity of these findings was questioned due to the lack of a control group. 31,32The present study can confirm the results of the previous studies.The increase in the rate of fetal distress in newborn observed in mothers with COVID-19 in the present study reinforces the hypothesis that COVID-19 can act as a mediator and ultimately increase preterm delivery. 152][33] The cause of this finding is not known yet, but it might be due to preterm delivery or premature rupture of membranes (PROM).Therefore, fetal monitoring is recommended for early detection of these cases in the acute phase of the disease.
Increased incidence of cesarean delivery in pregnant women with COVID-19 has been previously reported 15,34 and was similar to the findings of the present study.Cesarean delivery is not directly related to COVID-19 severity in mother or fetus.Only a few studies reported that Caesarean section was performed due to maternal complications and fetal distress related to COVID-19.As a result, other clinical and non-clinical factors, including preeclampsia, preterm delivery, management of maternal respiratory disease, and the need to expedite delivery to stabilize mother's condition, improve maternal ventilation and prevent vertical transmission, should be considered in choosing the method of delivery.However, no contraindications for Caesarean section in pregnant women with COVID-19 have been reported yet. 15Th increased rate of Caesarean section and preterm labor may potentially be due to iatrogenic reasons. 33imilar to the findings of the present study, an increase in the incidence of low birth weight has been reported in other studies. 28Preterm delivery may be associated with increased prevalence of low birth weight and higher rates of NICU admission.It is important to note that COVID-19, as an acute infection, may have minor effects on birth weight.However, serial ultrasound assessments to evaluate the risk of IUGR is recommended in early pregnancy infections, and in pregnant women with chronic hypoxia. 34Furthermore, a systematic review showed that the most common obstetric findings in pregnant women with COVID-19 were preterm delivery, preeclampsia, hypertension, fetal distress, and fetal growth restriction. 35he present study showed a statistically significant difference in the health status of the infant between pregnant women with COVID-19 and non-infected women.In another study, the incidence of IUGR, LBW and NICU admission was higher in neonates born to an infected mother compared to the non-infected group. 368][39][40] Thus, decrease in ACE2 due to COVID-19 may be a risk factor for placental vascular dysfunction, maternal hypertension, and adverse pregnancy-related consequences of placenta dysfunction, as well as exacerbation of pre-existing conditions in pregnancy.
These complications may lead to increased incidence of IUGR or exacerbation of pre-existing IUGR. 37One study also showed that the rate of severe neonatal complications, including NICU length of stay of 7 days or more, as well as severe neonatal complications and their components, were significantly higher in women with COVID-19 compared to non-infected pregnant women.Increased neonatal risk persisted after adjusting for the effect of history for preterm delivery and preterm delivery in the current pregnancy.Therefore, it is possible that COVID-19 may have direct effects on adverse neonatal outcomes. 41he present study showed that the number of live children was significantly higher in pregnant women with COVID-19 compared to non-infected pregnant women.2][43][44][45][46] Although COVID-19 is a disease that has resulted in a large death toll, it is not yet possible to determine whether these deaths are related to COVID-19 infection. 44,47n the present study, the rate of breastfeeding was lower in infants of infected mothers compared to noninfected mothers.Some studies reported that the rate of breastfeeding was as low as 28.6% among women with COVID-19.Neonatal morbidity, low birth weight and preterm neonates, as well as inability of infected mother to breastfeed due to COVID-19 symptoms or pregnancy and childbirth complications are more common in these women.These factors may reduce the rate of breastfeeding and thus increase the need for formula feeding.One of the limitations of this study was the difficulty in matching the case and control groups.

Conclusion
The results of the present study showed that pregnant women are one among the vulnerable groups for COVID-19, based on the related risk factors, highrisk pregnant women should be prioritized to receive COVID-19 related health services.Women with COVID-19 were older and had higher incidence of abortions, obesity, and multiple pregnancies compared to the control group.However, based on the regression analysis, the effect of age, parity, and number of abortions was not significant.Lifestyle modification, evaluation and treatment of vitamin deficiency in preconception care and increasing the number of pregnancy care-related to abortions and preterm labor among pregnant women during COVID-19 pandemic is recommended.

Table 1 .
Comparison of maternal and obstetrics characteristics of the participants between the case and control groups

Table 2 .
Comparison of obstetrics complications between the case and control groups

Table 3 .
Comparison of the clinical characteristics of newborns between the case and control groups

Table 4 .
Regression analysis to determine the predictive role of maternal and obstetrics characteristics, obstetrics complications and newborn characteristics in differentiating women with COVID-19 from non-infected women RC = Reference, KMC = Kangaroo mother care, BMI = Body mass index, r = Pearson Correlation Coefficient, OR = odds ratio.Logistic regression analysis.Bold values indicate statistically significant relationship.