The aim of this study is to examine the effectiveness of a programme to improve healthy lifestyle behaviours based on the Health Belief Model to be offered through Instagram, a social media platform. For this purpose, it is aimed to produce content containing accurate and evidence-based information for pregnant women on social media, to ensure that pregnant women can access the right information quickly and easily, to adopt healthy lifestyle behaviours, to test the effectiveness of the social media platform for the adoption of healthy lifestyle behaviours and to contribute to the formation of a healthier family and society in the long term. In addition, this study is aimed to create a model for the midwifery profession to benefit from the new opportunities created by internet technology outside the clinical field in service delivery.

The population of the study will consist of women with primiparous pregnancies in the first and second trimester. Women who agree to participate in the study will be randomly assigned to the experimental and control groups. In addition to routine care and counselling, pregnant women in the experimental group will receive support for developing healthy lifestyle behaviours through Instagram, while the control group will receive only standard pregnancy care and counselling services approved by the Ministry of Health.

General Hypothesis of the Study:

H1: The Healthy Lifestyle Behaviours development programme offered through the social media platform Instagram is effective in providing a positive development on healthy lifestyle behaviours in pregnant women.

Maternal health covers women's health during pregnancy, childbirth and the postnatal period. Despite significant progress over the last two decades, 287,000 women are reported to die during pregnancy, childbirth and the postnatal period in 2020. Adopting healthy lifestyle habits from pre-pregnancy to the postnatal period is crucial for healthy pregnancies and the prevention of diseases that can occur during pregnancy. Pregnant women are advised to adopt healthy eating habits, consume adequate nutrients, balance the body's extra demands and maintain physical activity to maintain good health and prevent excessive weight gain. The World Health Organisation warns pregnant women about nutrition, physical activity, stress management and avoiding toxic substances. High-quality evidence shows that diet, exercise or both interventions can significantly reduce the risk of excessive pregnancy weight gain compared with routine care. These interventions may reduce maternal hypertension, neonatal respiratory distress syndrome, caesarean section, macrosomia. Today, a large part of our lives is dominated by mobile phones, computers and household appliances that operate over the Internet. In this way, people can communicate with each other and transfer information to each other without time and space barriers. Social media, defined as online networking sites that enable Internet users to communicate through activities such as content sharing and personal comments, has become a widely used term for sharing information and ideas on the Internet or mobile platforms. The literature shows that the use of social media has become widespread in pregnancy care. In a meta-analysis of fifteen randomised controlled trials, social media and mobile health applications were found to be effective in supporting maternal physical health in pregnant women in conditions such as weight management, gestational diabetes control, asthma control. At the same time, it has been observed that it improves maternal mental health and increases women's level of knowledge about the pregnancy process.

With the current study, it is aimed to implement the Healthy Lifestyle Behaviour Development Programme to be created based on the Health Belief Model in pregnant women through the social media platform, which is frequently used today, and to contribute to the development of mother-baby health by providing pregnant women with instant and easy access to the right information.

Inclusion Criteria:

• First and second trimester pregnancy
• 18-49 years old
• With a singleton pregnancy
• Able to use web and mobile devices
• Has an account of the determined social media platform and actively uses it
• Can read and write Turkish
• Pregnant women with regular internet access were included in the inclusion criteria of this study.

Exclusion Criteria:

• Has a psychiatric problem that prevents communication
• Have a serious pre-pregnancy condition (heart disease, kidney disease or other chronic disease)
• Previously used a similar programme or app to change healthy lifestyle habits
• Risky pregnancies (heart disease, kidney disease or other chronic diseases)

The group to be trained during their pregnancy consists of women.