This clinical descriptive study was prospectively performed at three different tertiary Danish hospitals in the Capital and the Zealand regions between February 2019 and October 2020. Yearly the three hospitals take care of between 2500 and 6000 deliveries. In Denmark the rate of preterm deliveries before gestational age 34 is approximately 1.5% and a diagnosis of threatened preterm delivery explains 31% of all antenatal obstetric hospitalisations . The use of recommended AR is not an intervention with a specific treatment or discharge code and its general prevalence is therefore unknown .
Women with singleton pregnancies, who were assigned to give birth at the included hospitals were eligible to participate in the study from gestational age of 22 to 33 if they had been recommended AR due to a diagnosis of threatened preterm delivery (preterm contractions with or without tocolysis treatment, short cervix < 20 mm assessed by cervical ultrasonic scan, vaginal bleeding, and/or PPROM) or if they had uncomplicated pregnancies and no recommended AR. Moreover, inclusion criteria allowed no allergies to band aid, no chronic diseases that affected the daily level of physical activities, and no immediate preterm delivery (no fibronectin testing were required according to Danish guidelines ). Further, participants had to be 18 years or older of age and be able to understand Danish in speaking and writing.
Recruitment took place at outpatient antenatal midwife clinics as well as at the emergency antenatal wards. The attending midwifes informed eligible women orally and in writing about the study. If a woman was interested a researcher approached her and informed in detail about the study. If accepting participation, the woman gave informed written consent and was then included in the study.
For seven days the study participant wore two accelerometric SENS motion® sensors attached with Micropore 3 M® band aid on the right side of the chest 3-4 cm below the clavicle and lateral from the sternum, and laterally on the right thigh 10 cm above the patella. The devices are waterproof, and the participants were therefore instructed not to remove them during bathing, swimming, and showering. During the study period participants could change the band aid if needed as additional Micropore 3 M® band aid and an instruction sheet was provided at the inclusion.
At inclusion the two accelerometric SENS motion® sensors were attached. If possible, the accelerometric data collection was initially validated by the registration of the five different physical positions and activities, each manually registered for 3 min by the researcher.
At inclusion demographic and obstetric data were collected including maternal age, parity, gestational age at inclusion, pregnancy complication, pregestational body mass index, educational level, work status, smoking status, partner status, and level of self-reported pregestational physical activity (high (competitive sports); moderate; light; sedentary) . Moreover, the admission status i.e. inpatient, outpatient, or combined in-/outpatient AR was registered at inclusion and during the data collection period.
Recommended AR was classified as strict, moderate and light respectively as described in details elsewhere . In brief, strict AR was in this study defined as supine or laid-back rest most of the waking hours of the day (> 8 h daily) except for meals and bathroom use; moderate AR as > 3-8 h rest and light AR as 3 h daily rest. It was the participant’s perception of the recommended restriction level that classified the AR, as the restriction level seldom was specified in the medical files. If the specific level (strict or moderate) of prescribed recommended AR was unclear to a participant, it was classified as ‘unspecified’.
The accelerometric data from SENS motion® sensors
The SENS motion® sensors collected accelerometric data of time spent in supine or lateral rest, upright sitting, upright standing, sporadic gait, walking and the number of steps taken . Hence, the study gathered data as a continuum of five different positions/movements between physical inactivity and physical activity. The measurements of time spent in the different physical positions and activities were recorded continuously throughout study participation by the two miniature tri-axial accelerometers (dimensions: 50 × 21 × 5 mm, weight: eight grams; SENS motion® PLUS activity measurement system, version 1.7.6). The system measures movements continuously at 12 Hz, 24 h a day. Data were analyzed in 5-s epochs, which each was estimated to belong to a certain physical activity category. The activity intensity was calculated as the average vector magnitude of the high-pass filtered 3 axis accelerometer measurements at 12 Hz sampling frequency subtracted the noise present on each measurement axis, done on each 5-s epoch.
Prior to data analyses a qualitative audit was performed by two of the researchers (JMB, MGB) in one third of the accelerometric data sets, which were randomly selected. To assure exact accelerometric measurements a qualitative comparison of the validation data and the study data was done and showed excellent compliance with 100% agreement in all cases.
Demographic, obstetric and accelerometric data were stratified according to level of recommended AR and presented as number (%) or median value (range min–max). The individual accelerometric data were plotted in different scatterplots stratified by level of recommended AR.
Linear regression models were used to test differences between the different gradations of AR. In two steps a general linear regression analysis was performed with the independent variables strict AR versus no AR and with moderate AR versus no AR. Adjustment was made for the a priori defined factors known to clinically influence time spent in physical inactive positions and in physical activities during pregnancy including gestational age, parity, admission status, educational status, and time monitored. Mann Whitney was performed to test the difference between strict AR during inpatient admission status and strict AR during combined in-/outpatient admission status. These data are presented as β [95% CI].
The statistical significance was defined as a p value of less than 0.05. All analyses were performed using SPSS 25 software (IBM. Corp., Denmark, Europe).
The study was approved by The Danish Data Protection Agency (VD-2018–305, I-Suite 6591). The Danish Regional Committee on Biomedical Research Ethics was notified about this study and the committee decided that ethical approval was unnecessary (Notification Request no. 18021398). The respective administrations of the obstetric departments at the three study sites all approved the study. At inclusion all participants gave written informed consent to participate.
All methods were carried out in accordance with the study protocol and other relevant guidelines and regulations.