Design
The study was conducted as a multicenter quantitative cross-sectional study. The reporting of the study follows the STROBE statement (12).
Recruitment and inclusion criteria
The sample included high school girls aged 15 to 19 years old, who already had their menses, and who attended school in Ille-et-Vilaine, Brittany, France. Girls who had experienced primary or secondary amenorrhea for more than 6 months in the past year were excluded from analysis. The period of inclusion was April and May 2019. A random sampling without replacement was performed to select eight private and public high schools, all levels included. In each high school, we asked the school nurse or the director to randomly select two or three classes from each year (10th to 12th grade) to include about 100 to 150 girls. The girls and their parents received information about the study around 10 days before inclusion; only adolescents who agreed to participate were included. In each high school, the participants were gathered in a classroom or the amphitheater with the main investigator and asked to complete an anonymous questionnaire of 50 questions. No boys were present to ensure that the girls felt free and confident enough to complete the questionnaire in the most frank way. After completion, which took about 20 to 30 minutes, the main investigator immediately retrieved the questionnaires. After the study, a health and drugs-information lesson was given to the adolescents to educate them about dysmenorrhea and how to manage it.
Outcome measures
The main outcome measure was the prevalence of dysmenorrhea, defined as painful menstruation with cramping sensation in the lower abdomen or lower back, occurring with the menstrual flow or the day before. Severity was assessed according to the intensity of pain, measured by a Numerical Rating Scale, and according to other factors by the Verbal Multidimensional Scoring System (VMSS) (13). More specifically, the VMSS assesses pain intensity, the presence of systemic symptoms, the impact on daily activities and the need for analgesic treatment. Grade 0 corresponds to the absence of dysmenorrhea, and grades 1, 2 and 3 to mild, moderate and severe dysmenorrhea, respectively. Grade 1, or mild dysmenorrhea was defined as painful menstruation which rarely required pain relief and seldom inhibited daily activities. Grade 2, was defined as moderately painful menstruation which affected daily activities, but with pain killers providing sufficient relief so that absenteeism was unusual. Grade 3, or severe dysmenorrhea, was defined as extremely painful menstruation associated with vegetative symptoms (headache, asthenia, vomiting, diarrhea), reduced daily activities, and no relief by pain killers.
Data collection
The 50-question self-assessment questionnaire collected socio-demographic information, the age of menarche, characteristics of the cycles (including length of the cycle and regularity, duration of the menses and perception of volume), the presence of dysmenorrhea, and the girls’ expectations for information about menstruation and dysmenorrhea. Only the girls who suffered from dysmenorrhea were asked to complete the second part of the questionnaire about menstrual pain, its features and repercussions. The girls were also asked about the way they managed their pain, whether they sought medical advice or not, used pharmacological or non-pharmacological treatment, or self-medicated. The questionnaire covered all the items of the VMSS (13).
Target number of participants
Due to the wide variation in the reported prevalence of dysmenorrhea, from 21 % to 94 % in the literature (8–10,14), the calculation of the required sample size was maximized using a prevalence of dysmenorrhea of 50%. With a precision of 5% and alpha-risk of 0.05, 385 subjects were needed. We decided to double the sample size to obtain sufficient responses for the second part of the questionnaire which was only completed by the girls who had dysmenorrhea (n=770).
Statistical analysis
The prevalences of dysmenorrhea and severe dysmenorrhea were calculated and a descriptive analysis of the population was carried out. Qualitative variables were described as numbers and percentages, and quantitative variables as numbers, means and standard deviation. For group comparisons, the Chi-square or Fisher’s exact tests were used for qualitative variables, and Student’s t-test or ANOVA for quantitative variables. The population was compared according to i) dysmenorrhea and ii) the severity of dysmenorrhea (grade 1, grade 2, grade 3). Chi-square or Fisher’s exact tests were used to compare the distributions of qualitative variables, as well as Student’s t-tests or ANOVA for quantitative variables. Risk factors for severe dysmenorrhea were identified by logistic regression and presented by Odds Ratios (OR) and their confidence intervals. Variables with a P-value lower than 0.15 in the univariate analysis were included in a multivariate model. Statistical analyses were conducted among the subgroup of adolescent girls without hormonal contraceptives. A P-value under 0.05 was considered as significant. To account for missing data (i.e., incomplete responses), percentage values were calculated according to the number of answers received for each question. All statistical analyses were performed using SAS V9.4 software (SAS Institute, Cary, NC, USA).