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).