This is a part of a prospective longitudinal cohort study that investigated the association between pelvic alignment and lumbopelvic pain during pregnancy. In the current study, the association between the use of pelvic belts and pelvic alignment in perinatal period was investigated by using the information of pelvic alignment and pelvic belt use. The current study was conducted adhering to STROBE guidelines.
Participants
Pregnant women were recruited from the Obstetrics and Gynecology clinics in Aichi Prefecture, Japan, between May and December 2014. The inclusion criteria: gestational age < 12 weeks and singleton pregnancy. Women with serious orthopedic disorders, neurological diseases, or high-risk pregnancies were excluded. Those who had already used pelvic belts as of the time of study recruitment were also excluded to remove any effects of pelvic belt use prior to pregnancy. Two hundred and fifty women who met the study inclusion criteria and agreed to participate were initially enrolled. Participants were observed during late pregnancy (30 ± 0.60 weeks of pregnancy) and after childbirth (31.5 ± 5.5 days after childbirth) in regular prenatal clinic visits. Among the initially enrolled participants, 13 and 36 women discontinued their participation during late pregnancy and after childbirth, respectively, for various reasons including hospital transfers, births that occurred before the late pregnancy investigation period, or personal feelings. Therefore, the data of 201 women were ultimately used in the analyses (Fig. 1).
Questionnaires
Personal characteristics (age, height, weight at the time of recruitment, pre-pregnancy weight, and number of previous deliveries) were recorded at the time of recruitment. In addition, weights were recorded at each investigation period and birth weight was recorded after child birth. The weight, number of deliveries and birth weight as well as age were investigated because they are thought to be related to pelvic alignment. Pelvic belt use from 24 weeks of pregnancy, and that after childbirth were reviewed during the late pregnancy and post-childbirth investigation periods, respectively. The patients were queried as to whether or not they used pelvic belts, as well as how many days per week and the times in each day that the belts were used. If the participants were unclear as to any parts of the questionnaire, the measurers (midwives or physiotherapists) were available to answer their questions.
Pelvic alignment
Measurement settings
Pelvic alignment was measured using a palpation meter (PALM, St. Paul, MN, Performance Attainment Associates, USA). The anterior width of the pelvis in centimeters was measured by placing the PALM caliper tips in contact with the bilateral anterior superior iliac spines (Fig. 2). The posterior width of the pelvis was similarly measured as the distance between the posterior superior iliac spines. The anterior pelvic tilts were measured bilaterally by placing the PALM caliper tips in contact with the ipsilateral anterior and posterior superior iliac spines (Fig. 2). This method is valid, reliable, and cost-effective for calculating any discrepancies between the patients’ landmarks [18]. During the pelvic alignment measurements, the participants took off their shoes and stood with their hands crossed in front of their chests. The left and right anterior pelvic sagittal tilts were measured in degrees.
Measured values
The difference in the bilateral pelvic tilts (in degrees) was defined as the pelvic asymmetry value. From the results of the measurements, the changes in pelvic alignment were calculated using the differences in the measurement values from late pregnancy to 1 month after childbirth. In addition, the anterior and posterior pelvic width values were divided by the participant’s height to obtain standardized values for the anterior and posterior pelvic widths.
Measurement accuracy
Before the measurements were taken, the measurers were taught the method of proper use of the PALM, which they practiced repeatedly. To verify measurement accuracy, the nine measurers separately measured the pelvic alignment of one woman using the above method. The verification procedure was repeated twice, at a two-week interval. The measurement procedure showed acceptable intra- and inter-rater reliability with intraclass correlation coefficients (ICC 1.1 and ICC 2.1) of 0.998 (95% CI 0.995–0.999) and 0.998 (95%CI 0.992–1.000), respectively, for the anterior pelvic tilt in this study. The ICC 1.1 and ICC 2.1 for the width of pelvis were 0.989 (95%CI:0.971–0.996) and 0.992 (95%CI:0.972–0.999), respectively.
Statistical analysis
At first, the participants were divided into four groups according to differences in pelvic belt use in late pregnancy and 1 month after childbirth to investigate the differences during and after pregnancy. Women who used the pelvic belt both during pregnancy and after childbirth were categorized as the “Before and After Childbirth” group (BAC group); those who used pelvic belts only during pregnancy were categorized as the “Before Childbirth” group (BC group); those who used pelvic belts only after childbirth were categorized as the “After Childbirth” group (AC group); those who did not use the pelvic belt at all during the maternity periods were categorized as the “Non-Use” group (NU group). One-way analysis of variance (ANOVA) with a post-hoc Tukey test for the interval scale, and a chi-square test for the nominal scale were used to evaluate differences in demographic characteristics such as age, height, weight before pregnancy, weight in each experimental period, number of previous childbirths, mode of delivery, and pelvic alignment (anterior pelvic width, posterior pelvic width and pelvic asymmetry). Next, an initial one-way ANOVA with post-hoc Tukey test was conducted to compare the amount of change in pelvic alignment from late pregnancy to post-childbirth between the groups. After the initial analysis, a multivariate regression analysis was performed to determine the statistically significant differences between the groups after the initial analysis to consider other factors that influenced pelvic alignment. The changes in pelvic alignment that showed statistically significant differences between the groups were specified as the dependent variables. The differences between the BAC and AC groups were specified as the independent variables, and the other factors associated with pelvic alignment (age, BMI in late pregnancy, number of previous childbirths, vaginal delivery and pelvic asymmetry in late pregnancy) [19, 20] were also specified as independent variables. Finally, we determined a set of cutoff points (“grouping cutoff points”) based on the length of time that the pelvic belts were worn. These grouping cutoff points were used to stratify the participants into the study groups. Cutoff points for use or non-use were increased from zero by evaluating the amount of time the pelvic belt was used in a week. Then, a one-way ANOVA with post-hoc Tukey test was conducted to compare the amount of change in pelvic alignment from late pregnancy to after childbirth between each group. Statistical analyses were performed using SPSS version 23.0 (SPSS, Chicago, IL, USA) with a significance threshold set at .05.