Proprioceptive, Fear-related and Inflammatory Factors in the Persistence of Pregnancy-related Lumbopelvic Pain.

The presence of PLPP will be questioned at each timepoint. PLPP will be defined as: "self-reported pain in the lumbar area, between the twelfth rib and the gluteal fold, with or without pain between the posterior iliac crest and the gluteal fold, articularly in the vicinity of the sacroiliac joints, that may radiate to the posterior thigh and could occur separately or in conjunction with pain in the symphysis pubis."

Upright standing balance control will be measured as center-of-pressure displacements with a force plate.

Center-of-pressure displacements in response to ankle muscle and lower back muscle vibration (60 Hz, 15s) during upright standing will be measured with a force plate.

Serum concentrations of inflammatory mediators will be measured.

Participants will be asked whether they are reluctant to perform any movement or activity in which their lower back or pelvis is involved, because they might have some concerns. If so, they are asked to specify the concerns and describe the movements or activities. For each of the activities, they will be asked to rate their (1) pain intensity, (2) perceived harmfulness, (3) fear, and (4) self-efficacy to perform the task, all via a Visual Analogue Scale (VAS) with 0= no pain/harmfulness/fear/self-efficacy to 100= maximal pain/harmfulness/fear/self-efficacy.

The SOC-13 contains 13 items, total score ranges 0 - 91.

The DASS-21 evaluates depressive mood, anxiety and stress in general: 21 items, total score per subscale (Depression, Stress, Anxiety) range 0 - 21. Higher scores indicate higher levels of depressive mood (DASS-21-Depression), anxiety (DASS-21-Anxiety) and stress (DASS-21-Stress).

The PRAQ-R2 evaluates pregnancy-related anxiety: 10 items, total score range 10 - 50. Higher scores indicate higher levels of pregnancy-related anxiety.

The EDS evaluates perinatal depression: 10 items, total score range 0 - 30. Higher scores indicate higher levels of pregnancy-related depression.

The PCS contains 13 statements on thoughts and emotions possibly related to the experience of pain, for which the participants rates her agreement: 13 items, total score range 0 - 52. Higher scores indicate higher levels of pain catastrophizing.

During the laterality recognition task, participants view 40 pictures of a model that has its lower back bent or rotated to the left or the right side. They will be asked to judge the direction of movement as quickly and accurately as possible. Average speed (in seconds) of response time and average accuracy of the answers (in %) will be recorded.

The FreBAQ assesses back-specific body perception: 9 items, total score range 0 - 45. Higher score indicate a more disturbed body perception.

The ODI is a 10-item self-report questionnaire that quantifies the extent of functional limitation in daily life due to low back pain. Each item is given a score between 0 (no limitation) and 5 (maximal limitation). The sum of the scores is multiplied by 2 to obtain a percentage score, with higher scores representing greater functional disability

The QBPDS assesses disability in individuals with low back pain and PLPP: 20 items, total score range 0 - 100. Higher scores indicate higher levels of disability.

The participants will be asked to rate the pain intensity at the lower back or pelvic girdle they experience at this moment (i.e., both at the start and the end of the full test procedure), the average pain intensity during the past week, the minimal pain intensity during the past week, and the maximal pain intensity during the past week, by using the Visual Analogue Scale (VAS, 0-100), with 0 = "no pain" and 100 = "the worst pain imaginable".

The participants will be asked how often they experience pain (1= some days, 2= most days, 3= every day)

The SF-36 evaluates health-related quality of life, 8 scales: physical functioning, role physical, bodily pain, general health, vitality, social functioning, role emotional, and mental health. Scores for the different scales are converted and pooled using a scoring key, for a total score ranging 0 - 100

The FABQ consists of 16 statements for which the participant rates her agreement with the statement on a scale from 0 ("completely disagree") to 6 ("completely agree"): 16 items, total score range 0 - 96). Higher scores on the FABQ indicated more strongly held fear-avoidance beliefs.

Individuals with PLPP will indicate the pain locations on a body chart.

Current body weight will be measured (kg)

Current fat mass and fat-free mass (in kg) will be measured using bioelectrical impedance analysis (Bodystat 1500, EuroMedix).

Current total body water (in liter) will be measured using bioelectrical impedance analysis (Bodystat 1500, EuroMedix).

In case the participant indicates pain in (one of) the PLPP regions (first criterium), the following clinical tests will be performed (second criterium) to confirm the presence of PLPP: thigh thrust, modified Trendelenburg test, Active straight leg raise test (ASLR).

The participant will perform the ASLR test in supine lying: she will be asked to lift one leg 20 cm off the bed, and a score between 0 and 5 will be assigned depending on the difficulty experienced (0= "not difficult at all, 1= minimally difficult, 2= somewhat difficult, 3 = fairly difficult, 4= very difficult, 5= unable to do).

The age of the participant will be noted (in years and months)

The participant will be asked: How would you describe your ability to make ends meet, considering your income and expenses?: With great difficulty, with difficulty, with some difficulty, fairly easily, easily, very easily

Marital status will be questioned (having a partner or not, living together/alone)

Highest obtained educational level will be recorded (i.e., primary education, secondary education, higher education (e.g., bachelor, master, PhD), currently in secondary education, currently in higher education)

Current job status will be recorded (i.e., paid full-time job, paid part-time job, in sick leave because of issues related to pregnancy but not due to PLPP, in sick leave because of PLPP, in sick leave for reasons not related to pregnancy or PLPP, paid job but currently on career break (e.g., pregnancy or maternity leave), unemployed, no paid job but unpaid volunteer work, student), and type of work (i.e., sedentary, manual work, heavy manual work)

The number of previous miscarriages will be recorded.

Smoking habits, including tobacco and vaping (i.e., daily, occasional, former, non-smoker) and number of cigarettes per day will be questioned.

Alcohol consumption (i.e., lifetime abstainer, former infrequent drinker, former regular drinker, current infrequent drinker, current light drinker, current moderate drinker, current heavier drinker) will be questioned.

Score on the International Physical Activity Questionnaire short form (IPAQ-SF).

All women will be asked whether they experience any recurrent or continuous pain apart from PLPP, and to indicate the pain locations on a body chart.

The PSQI assesses sleep quality over the past month: 19 items, global sleep quality scores range 0 - 21.

Height will be measured and reported in cm.

Pre-pregnancy body weight will be questioned and reported in kg.

The investigators will ask the participants whether they have sustained any falls during their current pregnancy (number of falls, gestational week during which fall(s) occurred, situation during which fall occurred (trip, slip, during stair ascent, during stair descent, during athletic activity), and injury severity associated with fall (no injury, mild injury requiring home treatment, major injury requiring medical attention))

Pelvic floor symptoms, i.e., urinary incontinence, fecal incontinence and pelvic organ prolapse will be assessed with the validated 20-item Pelvic Floor Distress Inventory (PFDI-20). The PFDI-20 contains 20 items, total score range 0 - 300.

The participants will be asked whether they worked in uncomfortable positions, performed irregular work, or did shifts during pregnancy and postpartum.

The participants will be asked if they have a history of low back pain, pelvic girdle pain or other (chronic) pain conditions.

The number of previous stillbirths and live births will be recorded.

The investigators will ask the participants whether they have sustained any falls during their previous pregnancy (number of falls, situation during which fall occurred (trip, slip, during stair ascent, during stair descent, during athletic activity), and injury severity associated with fall (no injury, mild injury requiring home treatment, major injury requiring medical attention))

The presence of urinary and anal incontinence during previous pregnancies (yes/no), and the recovery postpartum (full, partial, no recovery) will be questioned.

For each of the previous deliveries, we will ask birth weight, maternal age at time of delivery, delivery mode (vaginal, c-section), instrumented delivery (no, forceps extraction, vacuum extraction, fundal pressure), whether the delivery was induced (yes, no), whether a vaginal tear or episiotomy was present (episiotomy, tear, no), and whether the pregnancy was through assisted reproductive treatment (yes, no).

All participants will be asked whether they experienced PLPP during previous pregnancies (yes,no), and if yes, the total duration in weeks, the pain frequency (1= some days, 2= most days, 3= every day), whether they experienced one episode of PLPP or whether PLPP was recurrent or continuous, whether PLPP persisted postpartum and for how many weeks, and whether they sought medical help for PLPP and/or whether the pain was disabling or whether they required sick leave.