1. Background
Coronavirus Disease 2019 (COVID-19), caused by severe acute respiratory syndrome in Wuhan, Hubei Province of China, in December 2019, has become an epidemic affecting all countries worldwide (1-3). In March 2020, the World Health Organization (WHO) declared the disease caused by coronavirus a COVID-19 pandemicb (2, 4, 5). Although the disease is highly contagious, its main clinical symptoms are fever, dry cough, fatigue, myalgia, and shortness of breath. There are limited data on the effects of COVID-19, which affects all life periods of people, including pregnant women and fetuses. At the same time, the continuity of breastfeeding during this period poses a big problem. In the current scientific literature (6-8), breast milk is not accepted as a mother-to-baby transmission route for COVID-19 and other known respiratory viral infections. In a recent study by Chen et al., samples of amniotic fluid, cord blood, breast milk, and throat swab from babies taken from 6 out of 9 pregnant women in the third trimester were diagnosed with COVID-19 and confirmed by laboratory tests. Tests for SARS-CoV-2 in the samples taken were negative. It was reported that the test could not be performed because samples could not be taken from 3 mothers (9). The results of this study support that COVID-19 will not be transmitted through breast milk. In addition, skin contact between mother and baby has many benefits, such as strengthening mother-baby attachment, increasing breastfeeding rates, stabilizing the glucose level in the baby, and maintaining the baby's body temperature (10, 11). For this reason, it is seen that the importance of breastfeeding for mothers and babies should not be ignored since the level of evidence for the statements about not breastfeeding in mothers diagnosed with COVID-19 is low.
The World Health Organization (WHO), United Nations International Children's Emergency Fund (UNICEF), and Centers for Disease Control and Prevention (CDC) promote breastfeeding and mother-infant contact as long as adequate measures are in place to control COVID-19 infection. The WHO accepted breastfeeding as safe and emphasized the need for breastfeeding parents to wear a mask and ensure breast and hand hygiene (4).
According to the CDC, it was explained that if the mother's COVID-19 test is positive, the newborn should be isolated in a separate room, but this situation should not prevent mothers who want to breastfeed their babies. It has been reported that mothers should be encouraged to express milk during this process, and if possible, they should use a specialized breast pump for milk extraction. It has been stated that attention should be paid to hand hygiene while performing all these processes (6, 7). Providing breastfeeding during the pandemic is very important for maternal and newborn health. However, all mothers diagnosed with COVID-19 and those suspected of COVID-19 should receive comprehensive counseling and training from healthcare professionals on breastfeeding and expressing milk for their newborns (7). Breastfeeding during this period can cause anxiety in women for all these reasons (8). On the one hand, mothers who want to breastfeed their babies are afraid of infecting their babies with the COVID-19 virus. Breastfeeding mothers do not fully experience the emotional pleasure of breastfeeding because their anxiety levels increase while breastfeeding their babies despite applying all preventive measures (12). Therefore, breastfeeding mothers' feelings, thoughts, and experiences during the pandemic are very important for healthcare professionals. Determining their feelings and experiences is key in providing professional support to women during breastfeeding.
2. Objectives
This study aimed to determine women's breastfeeding experiences during the COVID-19 pandemic.
3. Methods
3.1. Design
This study was carried out using a qualitative approach. The data of the study were collected between January 2021 and March 2021.
3.2. Setting and Participants
This qualitative study was conducted in a research hospital in the Central Anatolian Region of Turkey. It involved 42 women who gave birth in the postpartum clinic on the first day of maternity (Table 1). There are two hospitals with maternity services in the province where the study was conducted. Since one of these hospitals was declared a pandemic hospital, it ended its service in obstetrics during the pandemic. This study was conducted in the postpartum service of the research and practice hospital, which does not work as a pandemic hospital in the same province and provides maternity services.
Table 1.Obstetric Characteristics of the Participants a
| Features | Values |
|---|---|
| Number of pregnancies | |
| Primiparous | 23 (54.7) |
| Multiparous | 19 (45.3) |
| Planning status of current pregnancy | |
| Planned | 33 (78.5) |
| Unplanned | 9 (21.5) |
| Having a health problem during pregnancy | |
| Yes | 4 (9.6) |
| No | 38 (90.4) |
| Baby's gender | |
| Female | 18 (42.9) |
| Male | 24 (57.1) |
| Birth type | |
| Vaginal delivery | 16 (38.1) |
| Cesarean delivery | 26 (61.9) |
| Average gestational age | 38.4 ± 2.3 |
| Average baby birth weight | 3146 ± 657.2 |
| Total | 42 (100) |
a Values are expressed as No. (%) or mean ± SD.
The population of this study consisted of women who gave birth in a research hospital in the Central Anatolia Region and were hospitalized on the first day of postpartum. Women who accepted the study and met the inclusion criteria were included in the study. Interviews were held with mothers who had breastfeeding experience during the COVID-19 pandemic, and the interviews were terminated with a total of 42 participants, considering that the data started to repeat and data saturation was reached. The number of participants was determined according to the "data saturation" principle, which is valid in qualitative research. A qualitative descriptive study was conducted through in-depth semi-structured interviews until data saturation. After data saturation in the qualitative sample, interviews with 42 pregnant women were terminated. There are studies with similar sample numbers on the subject (9, 10). Inclusion criteria for the study are as follows: participants must be between the ages of 18 and 35, able to read and speak Turkish, not diagnosed with COVID-19, have initiated breastfeeding after giving birth, have a healthy baby, not have any chronic diseases with the baby, and agree to participate in the study (Table 2). Exclusion criteria included women who did not have a baby with them, had a premature or postmature baby, or were foreign nationals.
Table 2.Characteristics of the Participants Regarding Breastfeeding During the Pandemic
| Features | No. (%) |
|---|---|
| Skin-skin contact at birth | |
| Yes | 23 (54.7) |
| No | 19 (45.3) |
| Previous breastfeeding status | |
| Lactating | 15 (35.7) |
| Not breastfeeding | 27 (64.3) |
| Breastfeeding time after birth | |
| Breastfeeding in the first 30 minutes | 20 (47.7) |
| Breastfeeding within the first hour | 16 (38.1) |
| Not remembered | 6 (14.2) |
| Total | 42 (100) |
3.3. Data Collection
The data were collected with an introductory information form aimed at determining the socio-demographic characteristics of women. Also, an interview form was prepared to determine women's feelings, thoughts, and experiences about breastfeeding in the in-depth interviews. The main questions were as follows. Based on your experiences as a breastfeeding mother:
- How do you think the pandemic will affect the breastfeeding process? Does giving birth during the pandemic worry you?
- What are your concerns about your baby and yourself?
- Do you think you are ready to breastfeed during the pandemic? How did you prepare? Did you receive information about breastfeeding during the pandemic before birth?
- What are you doing to protect your baby and yourself from COVID-19?
- What are your expectations from healthcare personnel regarding the breastfeeding process?
Probing questions, such as "Could you tell me more about that, please?" were asked to find additional data. The interviewer was free to ask additional questions to obtain more detailed information about the topics discussed. These questions were in addition to the ones he had prepared beforehand while still adhering to the overall structure and content of his prepared questions. A semi-structured interview technique, which is one of the qualitative data collection methods, involves using a predetermined set of questions and topics to guide the interview with participants. Different people's opinions on similar topics were disclosed in the interview form (13). The researcher collected data using face-to-face interviews with breastfeeding women in the gynecology and obstetrics clinics between January 2021 and March 2021 in the patient rooms following social distance and hygiene rules. The interviews were conducted in the participants' own rooms, in a quiet and uninterrupted environment. The participants selected the time for the interview themselves. A single observer collected the data through individual in-depth interviews. The interviews included a personal information form to gather the participants' characteristics and an interview form with semi-structured questions. The interviews lasted approximately 25 - 40 minutes. A voice recorder was used to record the data, and before starting the interview, each participant was informed that a voice recorder would be used, and their written and verbal consent was obtained. It was aimed to prevent data loss during conversations with voice recording. After the interview, the mother could get information about the research whenever she wanted by giving the interviewer's number.
3.4. Analysis
In the data analysis, the thematic analysis method was used to establish the themes and categories within the scope of the research. The recorded interviews were listened to and transcribed verbatim using the Microsoft Word program. After the interviews were transcribed, the researchers read each interview separately and repeatedly to determine what the interview meant as a whole. During the readings, the researchers independently marked the statements they found important and remarkable within the research framework and then created a code list from these statements to form a meaningful whole. The research themes were created by combining the codes that enabled the researchers to unite at the same points. Important phrases and codes were placed in appropriate themes. With the themes, it was ensured that the cases were better organized and made more understandable. The themes that were thought to be closely related were brought together and grouped. In addition to the researcher, support was received from two experts working in this field, who had qualitative research experience in creating themes and sub-themes, coding the data, and placing the codes under sub-themes and themes. Two experts created separate themes and sub-themes, and the themes were finalized. The research team used Lincoln and Guba's criteria to determine the reliability of the study. They explained that the reliability of a study is determined by credibility, dependability, transferability, and confirmability (11). The Four-dimension Criteria (FDC) were followed to assess the trustworthiness and rigor of the study.
Credibility: To create confidence that the results (from the participant's point of view) are accurate, reliable, and credible. For the interview guide, a pre-interview was conducted with two women selected from the postpartum clinic of the hospital where the study was conducted. The researcher had the knowledge and skills to fulfill previously acquired roles teaching midwifery students the research subject and managing qualitative nursing research projects.
Dependability: To ensure the consistency of the findings over time and the reproducibility of the findings if the research is carried out in the same context, on the same participants, and by the same coders. During the study, we drafted the research protocol in detail and created a detailed historical record of the data collection process in the study. To assess coding accuracy, constant communication was maintained among the research advisory team of the university where the study was conducted to ensure the protocol was followed.
Confirmability: To ensure that another external researcher can verify the study, the data are not from the researcher's point of view, and the study is data-driven. We developed detailed monitoring records of the data collection process. The research advisory team systematically reviewed the interview recording for coding accuracy. Triangulation techniques were applied to minimize research bias, ensure the objectivity of the data, and accurately reflect the participants' experiences and perceptions. In order to gain a holistic understanding of the experiences of postpartum women during the epidemic, a variety of data sources were obtained from women who were hospitalized in an emergency, referred from another hospital, or came by appointment from the outpatient clinic. Researcher diversity was provided by several discussions with the research advisory team with different perspectives. Methodological diversification was achieved by conducting a pilot interview followed by the main study interview. Upon completion of the data analysis, a draft was sent to the participants to receive their feedback and validate the findings. Participants agreed with the findings.
Transferability: To ensure that the results can be transferred and generalized to other settings or contexts, Sources of information for the study were selected through purposive sampling. An attempt was made to provide maximum variation to reflect a different sample. Simultaneous analysis was performed with data collection. This process was achieved by determining the number of newly generated codes, most of which emerged from the first meeting.
3.5. Ethical Considerations
Ethics committee approval was obtained from Bozok University Clinical Research Ethics Committee (Date: 11/12/2020: No.: 182). We also obtained written permission from the institution where the study was conducted. The willingness of the individuals to participate in the research group and the volunteering principles were explained, and informed consent was obtained.
4. Results
It was determined that the average age of the participants was 25.32 ± 0.9. Also, 50.0% were high school graduates, 71.4% were not working, 46.6% were equal to their income and expenses, and 45.2% were high school graduates (Table 3). Four main themes and 12 subthemes were developed, namely: Fear (Catching the disease, not being able to breastfeed, infecting the baby), Strain (Loneliness, lack of social support, feeling sad and inadequate), lack of knowledge (social isolation, compliance with hygiene rules, taking action) and requirement (need for information, expectation of help, increasing mother support) (Table 4).
Table 3.Socio-demographic Characteristics of the Participants (n = 12) a
| Characteristics | Values |
|---|---|
| Average age, mean ± SD | 25.32 ± 0.9 |
| Education status | |
| Secondary education | 8 (19.4) |
| High school | 21 (50.0) |
| University and above | 13 (30.6) |
| Working status | |
| Yes | 12 (28.6) |
| No | 30 (71.4) |
| Economic status | |
| Income less than expenses | 15 (35.7) |
| Income equal to expenses | 20 (47.6) |
| Income more than expenses | 7 (16.7) |
| Spouse education status | |
| Secondary education | 5 (11.9) |
| High school | 19 (45.2) |
| University and above | 18 (42.9) |
| Total | 42 (100) |
a Values are expressed as No. (%) unless otherwise indicated.
Table 4.Theme and Sub-themes
| Theme | Sub-themes |
|---|---|
| Fear | Catching the disease; Not being able to breastfeed; Infecting the baby |
| Strain | Loneliness; Lack of social support ; Feeling sad and inadequate |
| Lack of knowledge | Social isolation; Compliance with hygiene rules ; Taking action |
| Requirement | Need for information; Expectation of help; Increasing mother support |
Theme 1: Fear
Sub-themes: Catching the disease, not being able to breastfeed, and infecting the baby
Most participants stated that the COVID-19 pandemic negatively affected their babies' breastfeeding. During this period, most of them stated that they experienced "fear" intensely, including fear of not being able to breastfeed, fear of catching COVID-19 while breastfeeding, fear of having to stop breastfeeding, fear of constant contact with babies, fear of transmitting COVID-19 from hospital to baby, fear of staying away from baby, fear of decreased appetite of baby, and fear of COVID-19 transmission with breast milk. Some of the participants' experiences on this issue are given below.
A high school graduate, primiparous, who did not receive training on breastfeeding during the pandemic, P24:
"I could not sleep at all in the last months of my pregnancy; I was very afraid that I might catch COVID-19, they could hospitalize me, and I would not be able to breastfeed my baby; I am still afraid ..."
Participant no. 15, multiparous, who breastfed her previous baby, was afraid of giving birth during the pandemic and gave birth to a male baby with 3400 g at term:
"I am very afraid to infect my baby. I have touched him less. I think if I touched him less, he could not be infected..."
"The thought of being unable to protect my baby from the virus or of being sick and staying away from her scares me." (P26)
Theme 2: Strain
Sub-themes: Loneliness, lack of social support, and feeling sad and inadequate
Most participants stated that they had psychological/physiological difficulties in this process because they had to be alone and pay attention to hygiene rules due to social isolation rules.
A university graduate, multiparous, who received training on breastfeeding during the pandemic, P32:
"It is so hard ... I want to touch my baby, then suddenly I think that I did not wash my hands, I run to the sink immediately, I have pain as well..."
Other participants stated:
"No one around me (including my family) came to the hospital. It was very difficult to be alone in this process. I had a hard time caring for my baby." (P11)
"I feel very tired and have pain. I'm afraid something will happen to my baby if I sleep. I do not remember that I have had this much difficulty in my life." (P6)
Theme 3: Lack of knowledge
Sub-themes: Social isolation, compliance with hygiene rules, and taking action
Almost all participants (but one person who received support from a breastfeeding consultant) stated that they did not receive any training from health professionals on preventing COVID-19 while breastfeeding during the pandemic. Again, most of them stated that they got information about protection from COVID-19 from media and communication tools in general. One stated that they isolated themselves, wore masks, washed their hands, did not accept guests at home, had limited contact with their babies, did not leave the house, and took vitamin supplements.
Some of the participants' thoughts on this issue are given below:
"I definitely use disinfectant for my hands before touching my baby ..." (P3)
"I hadn't thought of contracting COVID-19. During my illness, I did not have a preparation plan for breastfeeding. Breastfeeding mothers need spare breast milk in the freezer for continuous breast milk delivery...." (P41)
"I think it can transmit an infection every time the nurse enters my room. During this process, the frequency of control can be reduced ... "
A university graduate, teacher, and primiparous (P19) stated that:
"Actually, I do not know how to protect against COVID-19 during breastfeeding; as far as I hear from the surroundings, I wash my hands frequently, and I do not touch anyone to my baby".
Theme 4: Requirement
Sub-themes: Need for information, Expectation of help, and Increasing mother support
It was found that most participants (28 participants) asked healthcare professionals to inform them in detail and support them more (psychologically and physiologically) in breastfeeding. Some (6 participants) stated that they did not want healthcare professionals to visit their rooms because they saw them as a source of infection.
A participant, multiparous (P18), who did not receive training on breastfeeding prior to the COVID-19 outbreak:
Other participants:
"They can be more informative. I wanted to use a silicone nipple, but he did not give information about how to use it…" (P41). (He wanted to use the silicone nipple to protect against COVID-19).
"They should motivate and give morale to mothers…" (P5)
5. Discussion
This qualitative study investigating women's COVID-19 breastfeeding experiences discussed four themes: (1) fear (sub-themes: Catching the disease, not being able to breastfeed, infecting the baby), (2) strain (sub-themes: Loneliness, lack of social support, feeling sad and inadequate), (3) lack of information (sub-themes: Social isolation, compliance with hygiene rules, taking action), and (4) expectation (sub-themes: Need for information, expectation of help, increasing mother support).
As long as the COVID-19 outbreak spreads rapidly, the number of patients will increase exponentially. There is no sufficient evidence to determine the effect of this infection on pregnant women, newborns, and children (14). But, there is no qualitative study on how COVID-19 affects postpartum women during breastfeeding.
Infectious disease is scary. The COVID-19 pandemic has caused people to experience widespread anxiety and fear. This fear may affect individuals' clear and realistic thinking (15). Restrictive measures taken during the pandemic can adversely affect mothers' mental health. It can increase the likelihood of developing anxiety, depression, or post-traumatic symptoms. Anxiety experienced after childbirth can prevent the mother from performing her maternal duties (16). The persistence of this emotional state for a long time affects the mother-infant relationship, including breastfeeding (14). In the systematic review by Yan et al., mental disorders were high among pregnant and postpartum women during the COVID-19 pandemic (17).
Studies addressing the psychological impact of the COVID-19 outbreak on pregnant and postpartum women are limited. However, a study found that anxiety and depressive symptoms were higher among the participants in similar groups than in the pre-epidemic. (18). One of the variables affecting mothers' breastfeeding success is their anxiety level. The high level of anxiety causes the mother to have difficulty participating in caring for her baby. The level of anxiety about breastfeeding and negative thoughts about the nutrition and adequacy of breast milk affect the mother's breastfeeding success (16). In light of the findings, most participants stated they experienced fear and anxiety in breastfeeding their babies during the COVID-19 pandemic. The findings are consistent with the literature. The COVID-19 outbreak has caused fear and anxiety for mothers who are breastfeeding their babies. This directly affected breastfeeding negatively. During the pandemic, nursing care planning for breastfeeding mothers became mandatory.
During the pandemic, the fear experienced by mothers may cause a decrease in breast milk, an increase in the risk of postpartum depression, and a deterioration of family processes. During the COVID-19 period, breastfeeding mothers are worried about the transmission of the virus to the baby through breast milk. There is no valid evidence that SARS-CoV-2 is transmitted through breast milk (19).
One of the factors affecting breastfeeding is the interaction between mother and baby. Delay in communication between mother and baby affects breastfeeding negatively (7). Mother-baby bonding can be achieved by providing skin-to-skin contact between mother and baby. This contributes to the increase in breastfeeding rates and the protection of the baby's blood glucose levels and body temperature (18). It also increases the mother's breastfeeding self-efficacy (20). Due to the transmission of the COVID-19 virus through the respiratory tract, the epidemic is the most actual and challenging barrier to skin-to-skin contact. Failure to contact skin-to-skin in the postpartum period may lead to pathological conditions in mother-infant attachment. In our study, women feared touching their babies. They did not touch their babies because of the risk of transmitting the disease. This prevented contact, one of the main purposes of breastfeeding. Thus, mother-infant interaction decreased. This situation negatively affected breastfeeding self-efficacy. It is emphasized that the COVID-19 epidemic negatively affects mother-infant interaction. However, health professionals do not share up-to-date information with mothers (that the virus does not pass into breast milk).
Isolation precautions during the pandemic limit women's access to social support systems postpartum. As such, they faced new and unforeseen dangers, potentially endangering their mental health. The existence of a social support network in women in the postpartum period can be considered an important protective factor for expectant mothers (21).
The isolation of social support systems in the postpartum period and concerns about direct COVID-19 transmission have complicated this process for many mothers. The exceptional circumstances of the COVID-19 pandemic and the ongoing implementation of social isolation measures can impact women's mental well-being, particularly during the postpartum period. Research on psychological factors highlights the role of social support in the promotion and success of breastfeeding. It has been stated that breastfeeding mothers with more social support have higher levels of self-efficacy in breastfeeding. Maleki-Saghooni et al. stated that there was a relationship between social support and breastfeeding self-efficacy in their study with 300 primiparous mothers. Breastfeeding self-efficacy was higher in mothers with a large social support network. It is emphasized that including all social support resources in the breastfeeding process and encouraging the mother in this regard will ensure the continuation of successful breastfeeding by increasing breastfeeding self-efficacy (21). Support provided in the postpartum period, such as in Turkish culture, is related to family-centered cultures. Children tend to turn to their parents for support in adulthood. Health-related concerns caused by the COVID-19 outbreak can potentially negatively impact Turkish culture within the framework of social and personal relationships. Many practices that are vital in preventing the spread of the disease conflict with these cultural values. Changes in family support systems caused by the COVID-19 epidemic may cause impairment in coping mechanisms, a feeling of loneliness, and an inability to fulfill the maternal role. The mothers emphasized that they could not receive social support during the postpartum period. They mentioned that the lack of social support negatively affects the breastfeeding process. Nurses could provide online breastfeeding support during the pandemic.
The WHO has recommended that mothers breastfeed exclusively for the first 6 months after birth and continue breastfeeding until age 2. It is strongly emphasized that breastfeeding should be maintained and protected during extraordinary situations such as epidemics (22). These recommendations protect the baby's health because breast milk actively and passively helps develop the baby's immune system against infections (23).
The psychological impact of COVID-19 and the related quarantine measures are a cause for concern for new mothers. Due to the epidemic's short- and long-term health effects, nursing mothers are neglected in breastfeeding counseling services. On the other hand, they are concerned about breastfeeding safety due to the COVID-19 threat (24). During the pandemic, breastfeeding mothers cannot access healthcare services face-to-face because of fear of COVID-19 or because they cannot reach healthcare professionals (25). To ensure successful breastfeeding, healthcare professionals should encourage the mother to breastfeed and provide good counseling by recognizing the mother's concerns about this issue (26, 27). Due to the COVID-19 outbreak, training for mothers in clinics has been suspended. Healthcare support for new mothers has declined globally as telehealth applications are preferred over face-to-face interviews. In health institutions, fear of exposure to COVID-19 may cause breastfeeding parents to be reluctant to receive health services (28). Since mothers do not know how the pandemic affects them or their babies, they can increase the stress they experience during breastfeeding. As stated in the findings, mothers lack knowledge about COVID-19 protection and expectations from healthcare professionals. The initiation and continuation of successful breastfeeding are affected by many factors. In societies with high levels of exposure to the epidemic, health systems, health services, and staff have directed their power to the care of COVID-19 patients. The health service needs of groups with other needs have been ignored (28).
Insufficient support in postpartum may turn into failure in breastfeeding. This may cause the baby to reject the breast. Motivation is the most changeable factor for healthcare professionals initiating and maintaining breastfeeding. Motivation is one of the strategies provided in the decision-making process for a woman to manage breastfeeding. Nurses contribute greatly to breastfeeding success by motivating the mother with the breastfeeding training they give to the mother (29). In a meta-analysis study conducted to assess the factors related to starting and continuing breastfeeding; Cohen et al. emphasized that the necessary education and support should be provided to the family for successful breastfeeding and that the development of multi-factor interventions on the subject could be informative (30). In our study, it was determined that women were deprived of both social support and nursing care. The inability to receive nursing care negatively affected breastfeeding. Health policies should provide nursing care under all circumstances. Healthcare systems should be adjusted accordingly.
The family should be informed so that breastfeeding can be continued during the COVID-19 pandemic. At the end of the birth, the mothers should be followed up after discharge, and training and counseling should continue. Nurses can play an active role in ensuring the continuity of follow-up.
5.1. Conclusions
This study shows that women giving birth and breastfeeding during the COVID-19 outbreak have to cope with new challenges in addition to the usual stress of being a new mother. Women may be vulnerable postpartum due to restrictions on access to social support systems and isolation. Healthcare providers should communicate more frequently and earlier with new mothers in the postpartum period. Counseling should be provided on promoting breastfeeding, prevention measures against COVID-19 infection, and initiating and sustaining mother-infant interaction after birth. General infection control measures should be taken and strictly followed. Nurses are responsible for supporting women and their families throughout this process. In the findings, the sub-themes of not being able to breastfeed and lack of social support were reported the most. We recommend appropriate educational and therapeutic interventions on how nurses, midwives, and other healthcare professionals can meet the needs of breastfeeding women during the pandemic.
5.2. Limitations
The social distance while collecting data during the pandemic may have damaged the sense of trust between the participant and the researcher. During the pandemic period, hospitals have imposed restrictions. Therefore, the study was conducted in a single center, and the results cannot be generalized to the population.
