Journal of Pregnancy and Child Health
Open Access

Breastfeeding is an important public health practice with numerous benefits for both mothers and their infants. It is estimated that encouraging breastfeeding can prevent 823,000 infant deaths and 20,000 mother cancer deaths per year [1]. The World Health Organization (WHO) recommends exclusive breastfeeding for the first six months, continued with the introduction of complementary foods. Unfortunately, exclusive breastfeeding rates for infants below 6 months of age is just 15% in Lebanon. Low breastfeeding rates are attributed to individual, societal, institutional and policy level challenges [2].

Lactation Support Providers (LSPs) play an important role in improving breastfeeding rates. LSPs are breastfeeding experts who may be accredited as an International Board accredited Lactation Consultant (IBCLSP), a Certified Lactation Counsellor (CLSP), or a Certified Breastfeeding Specialist (CBS). As professionals who have received specialized trainings to address the different needs of breastfeeding mothers and infants around the world, LSPs offer professional and evidence-based care [3]. LSPs advocate for breastfeeding as a crucial global public health imperative, strive to create supportive environments that facilitate an optimal breastfeeding experience for families, and educate resident physicians about breastfeeding, its assessment, and management. In Lebanon, they work on supporting and promoting breastfeeding through consultations in hospital, clinical and home settings. LSPs help facilitate the mothers’ experience primarily through improving her skills and enhancing her self-efficacy [4]. In fact, Lebanese women reported that they enjoyed having professional lactation support in both hospital and home settings, described their information and skilled as needed in society, and voiced out the importance of their support. However, barriers persist that hinder the management of breastfeeding difficulties and support of LSPs. Despite the evidence on the effectiveness of LSPs’ support in enhancing the breastfeeding journey, very little research is done on the experiences and challenges LSPs face [5]. This study explores the perceived barriers and facilitators of LSPs in delivering evidence-based support to breastfeeding women in Lebanon. Study findings aim at informing strategies and intervention that can improve the efficacy of breastfeeding support they provide.

Research design

This qualitative study was conducted using a grounded theory methodological design. Grounded theory was applied through an inductive approach that aims to explore the perceptions of LSPs and contributes to building a theoretical model that explores the barriers and facilitators LSPs face.

Setting and relevant context

The researchers announced the study and sought participants through closed social media groups of LSPs. A reminder message was sent through the same networks 2 weeks following the first invitation. A total of 8 interviews were conducted through participants who came forward and expressed their interest to participate in the study. The sample size was determined following the data saturation principle for generating knowledge needed in this study.

Sample

Eligible participants were lactation support providers who hold an IBCLSP, CBS, or CLSP and have worked for at least one year as a lactation support provider in Lebanon. The employment setting of the lactation support providers was in hospital, clinical and in home settings.

Data collection

The data collection period was from February 2023 till March 2023. The researcher contacted LSPs who have expressed interest in participating in the study and arranged appointments for in-depth interviews that were conducted to collect the data. Interviews with LSPs took place through an online meeting platform. The researcher read and explained the informed consent forms to all participants prior to the interview and their consent and signature was sought. A copy of the informed consent was given to participants. We asked LSPs open ended questions and implemented probing and prompting following an interview guide. All interviews were audio recorded and transcribed verbatim. Participation was voluntary and interview responses remained anonymous by using numeric codes in transcripts and reports. Data was generated based on one interview guide which included the following questions.

Data analysis

After collecting the data, the researcher transcribed the audio recorded interviews. Using the transcripts, the researcher manually coded the data, identified, and analyzed emerging themes. Thematic analysis was used which identifies, analyzes, interprets, and reports patterns within data, allowing for the simplest organization and detailed description of the data acquired. To organize these themes and check their presence in different transcripts, we needed to construct a matrix.

Thematic analysis involves several steps, including immersion in the data and developing initial codes. This process leads to a comprehensive list of codes that captures various themes present in the data. This method allows for a detailed examination of the data and allows researchers to identify significant and recurring themes, which can then be analyzed and interpreted. Overall, thematic analysis is a rigorous and systematic approach to analyzing qualitative data.

A total of eight participants were interviewed in this study. Participants were asked to describe their experience with providing breastfeeding support, highlighting barriers and facilitators. Several themes were identified in the analysis: Knowledge, community awareness, Health Care Provider’s (HCP) referral and support, HCP incompetence, Baby Friendly Hospitals (BFH), presence of LSP in non-governmental organizations, occupational support, decrease in formula marketing, healthcare system, economic crisis, COVID, cultural trust in white coat personnel, disintegrated breastfeeding in the culture, profession organization, competence of LSPs, and preference of a freelance job. These are presented using the different levels of the socio-ecological framework.

Individual women’s level

Knowledge (prenatal education): Participants attributed the discontinuation of breastfeeding to lack of prenatal breastfeeding education. Birthing mothers may find it difficult to absorb too much information at once due to their state of being pressured by family and providers, tired, and overwhelmed. Participants explained that mothers who take prenatal classes have greater confidence in managing breastfeeding challenges and make informed decisions.

“When a mom doesn’t know anything about breastfeeding, and hears about it after delivery, I will need to explain everything from point zero which can take between 2 to 4 hours. She will not be able to digest all of the information and will feel overwhelmed.” (Participant 1)

Knowledge (breastfeeding profession): Knowledge about the profession of LSPs makes it easier for mothers to seek support through direct communication with LSPs before and after giving birth, especially if faced with any breastfeeding challenge. This knowledge of the profession is largely gained through social media platforms and word of mouth.

“Social media is helping a lot. We are reaching more moms and spreading awareness on the importance of breastfeeding. In the past, that was much harder” (Participant 5).

Community level

Breastfeeding awareness: Several participants noted that a lack of awareness about breastfeeding among peers, spouses, and family members poses a significant barrier to the LSP’s ability to provide support. First time mothers are often influenced by their inner circle, and if the ones closest to her are not supportive of breastfeeding due to limited knowledge, it can be challenging for LSPs to provide adequate support even if the mother herself wants to breastfeed.

“New moms are most vulnerable and have the tendency to let the family affect their decision to breastfeed” (Participant 3).

Institutional level

HCP referral and support: Healthcare providers, particularly OBGYNs and pediatricians, can greatly facilitate access to lactation professionals. Their referrals affirm the need for LSP’s support so mothers will be inclined to contact a lactation professional to seek guidance. Referrals also enhance community trust in LSPs knowing that health care personnel are the ones referring to them.

“Of course, we are in contact with pediatricians that refer moms to us once they face breastfeeding problems” (Participant 2).

According to participants, the majority of pediatricians do not encourage breastfeeding due to the influence and incentives of formula companies, lack of evidence-based approach, and a lack of recognition of LSPs as professionals.

“Pediatricians know that there are lactation specialists, but they don’t tell moms. They directly tell her, oh give the baby formula. Not all of them are like this, but the majority are!” (Participant 5).

It is important to note that participants pointed out that some pediatricians do encourage breastfeeding, greatly facilitating LSP’s work by encouraging mothers to seek professional guidance.

“We have a portion of pediatricians who are breastfeeding friendly and encourage moms to follow up with us” (Participant 2).

HCP incompetence: There's a limited competence related to breastfeeding among HCPs, making them bound to negatively influence mothers’ decision through incorrect information that can negatively impact the decision to initiate or continue breastfeeding.

“We see disasters! Especially in hospital settings. The team starts to give the mom incorrect information that leaves her doubting herself if she really can breastfeed or not” (Participant 4).

Baby friendly hospitals: Participants explained how BFHs create a supporting environment through prioritizing breastfeeding, providing staff with proper training and resources, mandating the presence of an LSP as part of the staff, and respecting the role of LSPs.

“What eases things on the mom and I is the hospital. You can’t imagine the difference we see in baby friendly hospitals because the team is knowledgeable, and moms are informed that a lactation consultant will be visiting her” (Participant 5)

Participants voiced out that many hospitals in Lebanon are not baby-friendly majorly due to formula companies’ incentives and financial support. This diminishes the willingness of hospitals to adopt the baby friendly hospital initiative and accept LSP’s profession even if mothers themselves demand the LSP’s presence.

“The most difficult is the hospital because we sometimes are not allowed to go inside. They do not allow breastfeeding in their facilities” (Participant 8).

Presence of breastfeeding specialist in NGO: Participants believed that having LSPs present in non-governmental organizations and primary health care centers ensures equity in access to breastfeeding support to anyone residing within the Lebanese territories.

“The presence of a breastfeeding specialist in an NGO is necessary because we usually do field visits especially in vulnerable areas because we know that they cannot afford a breastfeeding consultation or may prefer paying for a medical consultation instead” (Participant 2).

Occupational support: The lack of a supportive work environment for breastfeeding mothers pressures them to discontinue breastfeeding and favor formula given the short maternity leave provided, absence of a private pumping area, and absence of pumping specific breaks.

“There needs to be a policy change, mothers can work shorter hours so they can go home sooner and have allocated pumping rooms so they wouldn’t go hiding in the bathroom and feel pressured by the manager” (Participant 7).

Policy level

Decrease in formula marketing: Participants noted that there wasn’t a significant change in formula usage even after the decrease in formula marketing since formula is still greatly present in hospitals, in pediatric clinics, and on market shelves. LSPs believe that this is primarily due to the lack of reinforcement and monitoring of Law 47/2008.

“There needs to be a policy that ensures that the formula marketing law is being followed. Having a law for the sake of the law means nothing if it isn’t implemented. It needs to include punishments for hospitals and pediatricians if they break the law” (Participant 8).

Healthcare system: The healthcare system in Lebanon is a hurdle for breastfeeding mothers as it does not recognize the significance of breastfeeding and prioritizes other minor health issues. The system does not aid mothers in returning to work by providing free or discounted pumps.

“We need a policy that requires hospitals to ensure that all HCPs working in the maternity and intensive floor units have basic training or at least have a clear reference sheet to give mothers who need help in breastfeeding. There needs to be a policy that allow more to have secured pump machines and to make renting a hospital grade pump cheaper” (Participant 7).

National level

Economic crisis: LSPs talked about the consequences of the Lebanese economic crisis on their services as many mothers are currently unable to book their services. LSPs are unable to decrease their prices for the same reason.

“Mothers do not realize that buying formula over the period of 6 months costs much more than having one consultation and follow up with a specialist, which is usually what most mothers need” (Participant 1).

However, the economic crisis was a facilitator to professional support due to a formula shortage, so many mothers who knew of an NGO hotline, free service, or are able to pay for the LSP’s services, preferred to breastfeed.

“Formula shortage and price made many families prefer breastfeeding and call us through the hotline” (Participant 2).

COVID-19: COVID-19 was a facilitator for breastfeeding support, given the awareness done on social media by LSPs and the establishment of a hotline by NGOs.

“When women knew about the immune benefits of breastfeeding during COVID, they were more inclined to breastfeed” (Participant 2).

Overmedicalized culture: Participants believe that the Lebanese society tends to unquestioningly trust physicians, which contributes to the widespread adoption of formula over human milk.

“We live in a culture that blindly believes doctors whether or not they speak the truth. The pediatrician directly tells mother that formula is same as breastmilk, so the mother believes” (Participant 1).

Disintegration of breastfeeding in the culture: Participants talked about family ties and their effect on breastfeeding. Lebanon's culture is family based where the family intervenes in nearly everything, leading to a flow of misinformation. Mothers do not feel encouraged to breastfeed in public due to the potential of shaming.

“They start telling moms all kinds of horrible stories and give her incorrect information. This makes the mom want to stop breastfeeding altogether or not even think of breastfeeding if she did not deliver yet” (Participant 7).

Professional and legal breastfeeding organization: Participants stressed on the importance of establishing a Lactation professional organization that could facilitate the formation of a fair and fixed price suitable for all mothers, monitor the scope of practice of LSPs, join efforts with power forces to improve communication and referrals between professions, and advocate for university curriculum update to enrich breastfeeding knowledge.

“We need to have a profession organization, order of lactation professionals. It ensures that you are going continuing education units, gives you sponsorship to conferences, and supports you to grow and become a board-certified lactation consultant” (Participant 6).

“It would be amazing if one day we have a professional breastfeeding organization because then we can join efforts with other associations like the one for doctors, because then it will improve the impact and reach” (Participant 7).

Preference of a freelance job: Participants acknowledged that freelance jobs offer more uninterrupted work time compared to hospital work, which is often interrupted by healthcare staff in maternity units.

“I used to work in a hospital, and it was hectic. Everyone interrupts and the mother then becomes unable to concentrate with me” (Participant 3).

This qualitative study is the first to provide insights on the barriers and facilitators lactation support providers perceive while providing breastfeeding support in Lebanon.

Prenatal classes empower and equip mothers with necessary skills and understanding to successfully breastfeed their babies, enabling them to make informed decisions. Participants expressed the importance of prenatal classes in increasing mother’s self-efficacy, highlighting the fact that even if a mother birthed in a non-baby friendly hospital, she advocates for her right to perform necessary breastfeeding practices. However, most prenatal classes are paid, making them inaccessible to mothers from certain socioeconomic backgrounds. This leaves many expecting mothers unable to access classes due to financial barriers. Free classes are limited, with only a few baby-friendly hospitals providing them. Greater efforts are needed to ensure equitable access to prenatal classes for all mothers. Previous research confirms the importance of breastfeeding classes in increasing mother’s self-efficacy to initiate and continue breastfeeding [6-9]. Participants recommended that prenatal classes should be attended by both parents to increase breastfeeding support. With the partner being educated on breastfeeding, they would have a better understanding of the challenges associated with it and can provide support to the mother. This creates a supportive environment that can encourage the mother to breastfeed confidently. Participation of spouses in prenatal classes has been found to enhance a mother's self efficacy towards breastfeeding, as research has shown that such participation helps to increase the confidence levels of mothers, leading to improved continuation rates of breastfeeding [10,11]. Further investigation is required to understand the effectiveness of prenatal breastfeeding classes and their ability to enhance self-efficacy among mothers in the Arab region. This knowledge can contribute to developing tailored programs and interventions that address the unique needs of Arab mothers and improve their breastfeeding outcomes. According to participants, mothers who have taken prenatal classes have prior knowledge of lactation support providers and their profession, primarily through social media that has become a crucial channel for lactation support providers to connect with mothers. In the past, fewer women were aware of this profession due to the limited prevalence of social media. However, with the rise of social media platforms, more women are now informed about lactation support providers and their services. Due to Lebanon's primary language being Arabic and the country hosting refugees from Arabic speaking countries, it is essential for lactation support providers to provide information in Arabic to avoid language barriers. Unfortunately, many providers offer their services in English, which can prevent mothers and families from receiving the support they need. To address this issue, lactation support providers should prioritize providing information in both Arabic and English to ensure proper communication. Our findings align with previous studies, having social media become an essential tool for networking and support, enabling users to benefit from valuable knowledge that further explains its positive influence it on breastfeeding practices [12-17]. Participants found that word of mouth played a significant role in expanding their reach to more mothers. Sharing success stories and positive experiences with lactation support providers, such as lactation consultants, inspired women to seek professional guidance for their own breastfeeding journeys. This highlights the importance of building a supportive network for breastfeeding mothers, as communities can play a crucial role in promoting positive breastfeeding outcomes. The effectiveness of promoting lactation services through word of mouth remains uncertain, as research has produced inconclusive results. Further research is needed to determine whether word of mouth can effectively promote the use of lactation services.

Institutional practices and policies, and HCP’s competence can influence the ability to provide breastfeeding support. Our findings indicate that BFHs facilitate lactation support provider’s ability to offer early breastfeeding support. This follows prior studies that indicate how BFHs have shown significant improvements in breastfeeding rates through educating HCPs, training HCPs, and providing patient counseling on breastfeeding [18,19]. BFHs can also facilitate the effectiveness of lactation support provider’s support through having them as an integral part of the maternity unit and enhancing interprofessional communication [20,21]. The limited number of BFHs in Lebanon has resulted in the majority of HCPs lacking competency in breastfeeding support. This problem still remains, leaving HCPs ill-equipped to assist breastfeeding mothers. Due to the financing it requires and the economic crisis Lebanon faces, hospitals are not likely to address the issue without legal obligations.

Participants consider pediatricians as the HCPs of greatest influence. Unfortunately, the majority of pediatricians resist acknowledging lactation support providers, encourage human milk substitutes use, and lack basic breastfeeding knowledge. Pediatricians may endorse human milk substitutes due to financial incentives from companies manufacturing them or lack of information on previous research. Literature confirms that a major factor of increased human milk substitutes use is actually due to pediatricians’ advice. Interestingly, there is a divide among pediatricians when it comes to working with lactation support providers. Some acknowledge and collaborate with them, while others believe that they are the only source of guidance for mothers. This attitude warrants further investigation, as the current discrepancy impacts a mother's breastfeeding experience and could lead to gaps in care.

Participants called for national-level changes, particularly the establishment of a legal organization for lactation support providers. As described by participants, the lack of a definite organization weakens the profession since not all providers have the same line of work. Therefore, monitoring the scope of practice through an organization can enhance the profession’s credibility as all providers’ support will be in alignment. Future research is needed to investigate whether or not the same difference in practice among lactation support providers is prevalent in the Arab region. This organization can partner with NGOs to secure funding for breastfeeding projects and advocate for the recruitment of more lactation support providers. This can promote equity in lactation services, making them more accessible to citizens, regardless of socioeconomic status. Further research is needed to determine if lactation support providers who work with NGOs can effectively promote equity in support as there is currently insufficient evidence to support this claim. As such, future studies should be conducted to determine if this approach can improve equitable access to lactation support for all women, particularly those from marginalized communities.

A legal organization can collaborate with different professional bodies such as the Lebanese society of obstetricians and gynecologists, the Lebanese pediatrics society, the midwifery association and the order of nurses to bring out hospital policy changes through interprofessional efforts and to through accepting the role of lactation support providers. This is supported by research, noting that an interprofessional approach is key to minimizing barriers and enhancing breastfeeding practices.

Another change deemed necessary by participants was the update of university and internship curriculums, particularly in health professions such as nutrition, midwifery, nursing, and medicine. As there is currently no emphasis on breastfeeding in these programs, HCP’s knowledge and skills required for breastfeeding promotion is inadequate. Many medicine and nursing students struggle with assessing and managing breastfeeding-related problems due to the limited breastfeeding information taught at university, as per previous studies. Therefore, this knowledge gap needs to be addressed through incorporating breastfeeding education into curriculums as previous findings show significant improvement in both knowledge and attitude towards breastfeeding of HCPs after curriculum was changed. However, universities may be resistant to curriculum changes in many majors due to longstanding curriculums. Given the extensive remodeling that would be required, introduction of policies is necessary to address this educational shift and encourage universities to embrace change. If this gets implemented, then regardless of whether the hospital follows baby-friendly protocols or not, HCPs will ultimately follow the needed breastfeeding practices given the change in mindset and impact staff already working in the hospital as they will be able to learn and adapt to the new updated practices. This approach could also foster greater appreciation and respect for the role of lactation support providers among HCPs.

Future research is needed to explore pediatrician’s perspectives to explain their resistance towards accepting LSPs. Research also needs to identify strategies to enable LSPs in forming a professional organization and to integrate LSPs in hospitals and NGOs. This is important to lessen the barriers LSPs face and to increase the effectiveness of their support.

LSPs role is crucial in enhancing breastfeeding rates in Lebanon, with the growing need of birthing women for guidance and support. The hindering and facilitating factors are indicative of the multi-level changes needed to strengthen the profession, particularly the individual, institutional, and national level changes discussed. An interprofessional approach with healthcare providers is necessary to solidify LSP’s role in the community and enhance the efficacy of their support. Interdisciplinary collaboration is necessary to enable LSPs to be better integrated in institutional and professional associations, to ensure equity in access to professional support and to strengthen the profession as a whole.

1. Victora CG, Bahl R, Barros AJ, Franca GV, Horton S, et al. (2016) Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect. Lancet 387: 475-490.

   [Crossref] [Google Scholar] [PubMed]

2. Anstey EH, Coulter M, Jevitt CM, Perrin KM, Dabrow S, et al. (2018) Lactation consultants’ perceived barriers to providing professional breastfeeding support. J Hum Lact 34: 51-67.

   [Crossref] [Google Scholar] [PubMed]

3. Amir LH, James JP, Kelso G, Moorhead AM (2011) Accreditation of midwife lactation consultants to perform infant tongue‐tie release. Int J Nurs Pract 17: 541-547.

   [Crossref] [Google Scholar] [PubMed]

4. Kabakian-Khasholian T, Nimer H, Ayash S, Nasser F, Nabulsi M (2019) Experiences with peer support for breastfeeding in Beirut, Lebanon: A qualitative study. PloS One 14.

   [Crossref] [Google Scholar] [PubMed]

5. Lee YH, Chang GL, Chang HY (2019) Effects of education and support groups organized by IBCLSPs in early postpartum on breastfeeding. Midwifery 75: 5-11.

   [Crossref] [Google Scholar] [PubMed]

6. Oliveira IBB, Leal LP, Coriolano‐Marinus MWDL, Santos AHDS, Horta BL, et al. (2017) Meta‐analysis of the effectiveness of educational interventions for breastfeeding promotion directed to the woman and her social network. J Adv Nurs 73: 323-335.

   [Crossref] [Google Scholar] [PubMed]

7. Parry KC, Tully KP, Hopper LN, Schildkamp PE, Labbok MH (2019) Evaluation of Ready, Set, BABY: A prenatal breastfeeding education and counseling approach. Birth 46: 113-120.

   [Crossref] [Google Scholar] [PubMed]

8. Ahlers-Schmidt CR, Okut H, Dowling J (2020) Impact of prenatal education on breastfeeding initiation among low-income women. Am J Health Promot 34: 919-922.

   [Crossref] [Google Scholar] [PubMed]

9. Namasivayam V, Dehury B, Prakash R, Becker M, Avery L, et al. (2021) Association of prenatal counseling and immediate postnatal support with early initiation of breastfeeding in Uttar Pradesh, India. Int Breastfeed J 16: 1-11.

   [Crossref] [Google Scholar] [PubMed]

10. Rabiepoor S, Khodaei A, Valizadeh R (2019) Husbands’ participation in prenatal care and breastfeeding self-efficacy in Iranian women: A randomized clinical trial. Med J Islam Repub Iran 33: 58.

    [Google Scholar] [PubMed]

11. Ranjkesh F, Soltanshahi Z, Azh N, Griffiths M (2020) Effect of spouse's participation in childbirth preparation classes in the promotion of social support among pregnant women: A field trial. Soc Health Behav 3: 55-61.

    [Crossref] [Google Scholar]

12. McCann AD, McCulloch JE (2012) Establishing an online and social media presence for your IBCLSP practice. J Hum Lact 28: 450-454.

    [Crossref] [Google Scholar] [PubMed]

13. Bridges N, Howell G, Schmied V (2018) Exploring chest/breastfeeding support on social media. Int Breastfeed J 13: 22.

    [Crossref] [Google Scholar]

14. Marcon AR, Bieber M, Azad MB (2019) Protecting, promoting, and supporting breastfeeding on Instagram. Matern Child Nutr 15: e12658.

    [Crossref] [Google Scholar] [PubMed]

15. Regan S, Brown A (2019) Experiences of online chest/breastfeeding support: Support and reassurance versus judgment and misinformation. Matern Child Nutr 15: e12874.

    [Crossref] [Google Scholar] [PubMed]

16. Wilson JC (2020) Using social media for breastfeeding support. Nurs Women's Health 24: 332-343.

    [Crossref] [Google Scholar] [PubMed]

17. Orchard LJ, Nicholls W (2022) A systematic review exploring the impact of social media on breastfeeding practices. Curr Psychol 41: 6107-6123.

    [Crossref] [Google Scholar]

18. Vasquez MJ, Berg OR (2012) The Baby-Friendly journey in a US public hospital. J Perinat Neonatal Nurs 26: 37-46.

    [Crossref] [Google Scholar] [PubMed]

19. Clermont A, Gemayel JE, Hammoud R, Wang J, Beciu H, et al. (2021) Effects of a ‘Baby-Friendly Hospital Initiative’on exclusive breastfeeding rates at a private hospital in Lebanon: an interrupted time series analysis. BMC Pregnancy Childbirth 21: 385.

    [Crossref] [Google Scholar] [PubMed]

20. Mosher C, Sarkar A, Hashem AA, Hamadah RE, Alhoulan A, et al. (2016) Self-reported breast-feeding practices and the Baby Friendly Hospital Initiative in Riyadh, Saudi Arabia: prospective cohort study. BMJ Open 6: e012890.

    [Crossref] [Google Scholar] [PubMed]

21. Walsh A, Pieterse P, Mishra N, Chirwa E, Chikalipo M, et al. (2023) Improving breastfeeding support through the implementation of the Baby-Friendly Hospital and Community Initiatives: a scoping review. Int Breastfeed J 18: 1-18.

    [Crossref] [Google Scholar] [PubMed]