Materials and methods
The study was designed in three phases, aimed at determining validity and reliability, and it was reported according to the Guidelines for Reporting Reliability and Agreement Studies (GRRAS) ( Kottner et al., 2011 ). Firstly, identification of DOHaD awareness scale dimensions and its components were defined. Secondly, DOHaD awareness scale was developed and validated. Then, a confirmatory study was carried out to ensure validity of the scale. This research was carried out in Kastamonu University Faculty of Health Sciences, first year Nursing Department female undergraduate students between 2018–2020. This study was approved by the Hacettepe University Non-interventional Clinical Researches Ethics Board (reference number GO 18/764-19).

Phase1: Identification of DOHaD awareness scale dimensions and its components

A comprehensive literature review through PubMed, ISI, ScienceDirect, Scopus and Google Scholar was conducted to identify concepts of DOHaD awareness and its components. The following keywords were used: “developmental origins of health and disease”, “developmental stage”, “childhood growth”, “pregnancy”, “pre-conception”, “transgenerational”, “knowledge translation”, “non-communicable disease risk”, “primary non-communicable disease prevention”, “health literacy”. Later, reference lists of the studies with these keywords were assessed for additional related research.

Phase 2: Development and validation of the scale

Using the concepts determined at phase 1 and evaluating existing questionnaires a pool of items was generated to measure DOHaD awareness ( Bay et al., 2012 ; Oyamada et al., 2018 ; Woods-Townsend et al., 2018 ; McKerracher et al., 2020 ). Then, item pool was reviewed and twenty items most relevant to the concept were selected. Inclusion for validation items was performed by a panel of five experts who had PhD degrees in Nutrition and Dietetics, and the initial questionnaire assessed for qualitative content validity. The experts were asked to comment on the necessity, relevance, clarity and simplicity to calculate content validity ratio (CVR) of each item with Likert-type phrases scoring 4 for “absolutely appropriate”, 3 for “appropriate”, 2 for “acceptable after edition” and 1 for “absolutely inappropriate”. CVR was calculated by the formula: [sum of experts scored 3 and 4/(sum of experts scored 1 and 2/2)] − 1 ( Lawshe, 1975 ). After reviewing and editing two items, CVR reached to an acceptable value of 0.80. Content validity and expert panel review led to acceptation of 20 items. The second draft of the scale consisted of 20 Likert-type items. The 5-point Likert-type scale was designed to increase 1 point for each option from none (one point) to severe (five points) and takes values between 20 and 100 points (no items were reverse scored). Thus, the scores 1, 2, 3, 4 and 5 correspond to “not at all”, “slightly”, “moderately”, “very much” and “extremely”, respectively.

In order to assess the face validity of the scale, a convenience sample of 250 female nursing students, aged 23 ± 9 years and similar to the target group, was recruited. The sample size was set at 250 participants, following the guideline of having at least ten times the number of observed variables in the scale ( Roscoe, 1975 ). Students were randomly chosen and interviewed to independently evaluate each item for clarity and complexity. All participants provided written informed consent. The data analysis involved exploratory factor analysis (EFA) to assess construct validity. In order to measure whether the scale can be modeled with a factor, the Kaiser-Meyer-Olkin Test (KMO) and Bartlett’s test of sphericity were performed.

The scale’s reliability was examined by employing internal consistency measures and a test-retest method. Cronbach’s alpha was determined to evaluate the internal consistency of the subscales to ensure reproducibility, the questionnaire was re-administered to 150 students aged 22 ± 10 years with a 2-week interval between tests. The average time taken to complete the questionnaire was 10 min. By the end of this phase, a final draft of the questionnaire comprising 20 items was created.

Phase 3: Confirmatory study

A scale was developed to assess awareness and understanding of DOHaD concepts. Furthermore, it was complemented by an educational module aimed at raising individuals’ awareness of the relationship between nutrition and DOHaD, as well as promoting the adoption of healthy eating habits. A different confirmatory study was conducted with 100 first year female nursing school students aged 21 ± 12 years to evaluate the impact of the education module. It should be considered that this study was conducted without a control group, which may act as a limiting factor in interpreting the findings regarding the effectiveness of the educational module. To assess consistency of results, the selected samples were different from those studied in the construct validity study. In this study, firstly, 24-h dietary recall, food frequency questionnaire, 24-h physical activity recall and anthropometric measurement records were taken, the Healthy Eating Index (HEI-2015) ( Krebs-Smith et al., 2018 ) score was calculated and the DOHaD awareness scale was applied. Despite the lack of a control group, after 4 weeks, an education module consisting of DOHaD concepts was given to participants by the research group.

The education programme consisted of a PowerPoint presentation including the topics of the description of fetal programming, DOHaD components, functions of placenta, importance of a healthy diet and physical activity, and introduction of dietary guidelines of Turkey. Then, problem-based learning, interactive question-answer and discussion techniques were applied to participants. The participants were given printed materials with narrative, examples and pictures containing the topics mentioned in the PowerPoint presentation. After 6 weeks and 6 months, 24-h dietary recall, food frequency questionnaire, 24-h physical activity recall and anthropometric measurement records were taken, the HEI-2015 score was calculated and the DOHaD awareness scale was applied again. Data collection conducted during February 2019 to October 2020. Confirmatory factor analysis was performed using the same parameters and fit indices as phase 2.

The participants’ body weights were recorded using a portable scale while they wore minimal clothing and no shoes. Height was measured using a wall-mounted stadiometer. Waist circumference was taken at the narrowest point between the iliac crest and the lowest rib, using an inflexible measuring tape. Hip circumference was taken at the highest point of the hip, parallel to the ground, using an inflexible measuring tape. Waist and hip circumference measurements were repeated three times, and the average values were calculated. All measurements were conducted as outlined in previous studies ( Hawes, 1992 ; Franco-Villoria et al., 2016 ). A single healthcare professional conducted all anthropometric measurements. Body mass index (BMI: weight/height 2 kg/m 2 ) and the waist-to-hip ratio were calculated and assessed based on the World Health Organization’s classification ( World Health Organization, 2010 , 2020 ).

The 24-h dietary recalls and food consumption frequency assessments were conducted through face-to-face interviews. The types and amounts of all foods and beverages consumed, along with recipes for prepared dishes and cooking methods, were documented and verified. A photographic atlas was utilized to capture the types and portion sizes of food, fluids, and meals ( Rakicioğlu et al., 2012 ). The dietary data were analyzed using the BeBIS-7 software program (Nutrition Information Systems Software), which facilitated the calculation of total energy intake, as well as macro and micronutrients ( Nutrition Information Systems, 2004 ).

The HEI-2005 was employed to evaluate the dietary quality of participants based on 24-h dietary recall data analysis. The HEI-2005 includes components that represent the major food groups: total fruits (worth five points), total vegetables (five points), total grains (five points), dairy products including soy beverages (10 points), and proteins such as meat, poultry, fish, eggs, soy products (excluding beverages), nuts, seeds, and legumes (10 points). Additional components consist of whole fruits (five points); dark green and orange vegetables, including legumes (five points); whole grains (five points); oils (notably non-hydrogenated vegetable oils as well as those in fish, nuts, and seeds) (10 points); saturated fats (10 points); sodium (10 points); and calories from solid fats, alcoholic beverages, and added sugars (20 points). The scores from the HEI-2005 were categorized as “poor” (≤50), “needs improvement” (51–80), and “good” (>80) ( Krebs-Smith et al., 2019 ; Reedy et al., 2018 ).

Participants were asked to record their PA patterns using a diary method that reveals the time spent in various activities (sleep, very light, medium, high, and very high). Energy expenditure was determined according to the activity type by multiplying the activity duration, PA ratio and PA levels. According to PAL values, participants’ physical activity status was classified as light (1.40–1.69), moderate (1.70–1.99) and vigorous (2.00–2.40), respectively ( Food and Agriculture Organization of the United Nations, 1985 ).

Exploratory factor analysis (EFA) was used to determine the quantity and quality of the scale factors. The Kaiser–Meyer–Olkin (KMO) test was used to measure sample adequacy. Bartlett’s globality test and explained total variance were used to evaluate factor analysis. Varimax rotation method was used in EFA. Factor loads were taken into consideration while deciding whether items should be deleted or kept. Internal consistency of scale items was determined by calculating the Cronbach alpha factor values. Test–retest reliability of the scale was determined using inter-class correlation (ICC) when the ICC > 0.75 was acceptable.

The significance of the difference between nutrition knowledge levels of matched groups before the education and after the study (20–100 points) was evaluated using t-test (paired) with the hypothesis of education increasing the level of awareness.

Data on qualitative variables were indicated using number/ratio charts, the difference between the groups was indicated using three categories of non-parametric test, and the the Marginal Homogeneity test for two dependent variables. Quantitative variables were indicated using mean, median, standard deviation, and top-bottom charts; evaluation of the normal distribution of data was made using the Kolmogorov–Smirnov test. If variables with more than two quantitative groups show normal distribution, repeated measures variance analysis (repeated measures ANOVA) was used; variables countering the normal distribution were applied to Friedman’s two-way ANOVA. The Wilcoxon test was applied in dependent variables non-parametric data to evaluate the difference between the test–retest results. Participants’ anthropometric measurements were evaluated over time, and the effects of the obtained results were assessed using Partial eta squared values. Partial eta squared is a measure of effect size that indicates the proportion of variance in the dependent variable that is explained by the independent variable.

In this study, generalized estimating equations (GEE) analysis was performed to evaluate the effects of DoHaD awareness scale and HEI-2015 scores on various dependent variables such as body weight, BMI, waist circumference, body fat percentage, and others over three different time points. The analysis used different correlation structures including AR(1), unstructured, exchangeable, and independent. A multivariate regression analysis was conducted to identify the factors influencing DOHaD awareness. All statistical analyses were conducted using SPSS 24.0 (SPSS Inc., Chicago, IL, USA).