82 Mottola MF, et al. Br J Sports Med 2019;53:82–89. doi:10.1136/bjsports-2018-099919 Is supine exercise associated with adverse maternal and fetal outcomes? A systematic review Michelle F Mottola, 1,2 Taniya S Nagpal, 1 Roberta Bgeginski, 3 Margie H Davenport, 4 Veronica J Poitras, 5 Casey E Gray, 6 Gregory A Davies, 7 Kristi B Adamo, 8 Linda G Slater, 9 Nick Barrowman, 6 Ruben Barakat, 10 Stephanie-May Ruchat 11 Review To cite: Mottola MF, Nagpal TS, Bgeginski R, et al. Br J Sports Med 2019;53:82–89. ► Additional material is published online only. To view please visit the journal online (http://dx.doi.org/10.1136/ bjsports-2018-099919). For numbered affiliations see end of article. Correspondence to Dr Michelle F Mottola, R. Samuel McLaughlin Foundation- Exercise & Pregnancy Laboratory, The University of London Ontario, London, ON N6A 3K7, UK; mmottola@uwo.ca Accepted 18 September 2018 Published Online First 18 October 2018 © Author(s) (or their employer(s)) 2019. No commercial re-use. See rights and permissions. Published by BMJ. ABSTRACT Objective Theoretical concerns regarding the supine position at rest due to the gravid uterus obstructing aorta and vena caval flow may impinge uterine blood flow (UBF) to the fetus and maternal venous return. Design Systematic review. Data sources Online databases up to 11 December 2017. Study criteria Eligible population (pregnant without contraindication to exercise), intervention (frequency, intensity, duration, volume or type of supine exercise), comparator (no exercise or exercise in left lateral rest position, upright posture or other supine exercise), outcomes (potentially adverse effects on maternal blood pressure, cardiac output, heart rate, oxygen saturation, fetal movements, UBF, fetal heart rate (FHR) patterns; adverse events such as bradycardia, low birth weight, intrauterine growth restriction, perinatal mortality and other adverse events as documented by study authors), and study design (except case studies and reviews) published in English, Spanish, French or Portuguese. Results Seven studies (n=1759) were included. ’Very low’ to ’low’ quality evidence from three randomised controlled trials indicated no association between supervised exercise interventions that included supine exercise and low birth weight compared with no exercise. There was ’very low’ to ’low’ quality evidence from four observational studies that showed no adverse events in the mother; however, there were abnormal FHR patterns (as defined by study authors) in 20 of 65 (31%) fetuses during an acute bout of supine exercise. UBF decreased (13%) when women moved from left lateral rest to acute dynamic supine exercise. Conclusion There was insufficient evidence to ascertain whether maternal exercise in the supine position is safe or should be avoided during pregnancy. INTRODUCTION Supine rest is associated with vena caval compres- sion and has been shown to result in symptomatic hypotension (secondary to reduced preload and cardiac output) in up to 10% of women. 1–3 Further- more, fetal oxygenation (as measured by fetal pulse oximetry) was lower in the supine posture at rest than in the left lateral position 4 due to maternal aortic compression. 5 Overall fetal well-being can be estimated from fetal heart rate (FHR) patterns, 5 6 which reflect fluc- tuations in parasympathetic tone and are linked to fetal central nervous system integrity and responses to oxygenation. 7 Changes in FHR patterns may be correlated with fetal distress (or varying levels of hypoxia) usually requiring prompt evaluation and potential change in maternal position. 6 Interpreta- tion of changes in FHR patterns can be complex; however, the absence of FHR variability (non-re- active) with recurrent late decelerations, recur- rent variable patterns or bradycardia may indicate hypoxia or adverse events. 6 The acute response to fetal reduction in oxygen is a reflex bradycardia; however, reduced FHR variability (<5 beats per minute (bpm)), tachycardia (>160 bpm) or absence of fetal movements may indicate fetal hypoxia. 6 In three recent observational studies, sleeping in the supine position may be associated with (1) stillbirth (OR 5.0, 95% CI 1.5 to 16.5 8 ; OR 2.54, 95% CI 1.04 to 6.18 9 ) and (2) fetal growth restric- tion in the last month of pregnancy (OR 5.0, 95% CI 1.2 to 20.2 10 ). The authors of these studies suggested that prolonged supine positioning poses an additional risk for vulnerable fetuses, such as those with low birth weight. Whether supine exer- cise is associated with these adverse outcomes has never been systematically examined. Given the potential clinical issues regarding the supine position at rest, it is plausible there could be maternal and fetal consequences to maternal exercise in the supine position. Indeed, a survey of guidelines for exercise during pregnancy from around the world showed that all but two (France and Spain) of nine countries (Australia, Canada, Denmark, France, Japan, Norway, Spain, UK and USA) cautioned against supine exercise after 16 weeks’ gestation. 11 However, in all cases the recommendation for caution was primarily based on expert opinion rather than explicit scientific evidence. The purpose of this systematic review was to determine whether prenatal supine exercise is associated with adverse outcomes in the mother and the fetus. The present systematic review was conducted as part of a series of reviews that informed the development of the 2019 Canadian guideline for physical activity throughout pPreg- nancy (herein referred to as the Guideline). 12 METHODS Protocol and registration This systematic review was performed in accordance with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) frame- work 13 and with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) harms checklist. 14 The protocol was registered a priori with the International Prospective Register on May 31, 2020 by guest. Protected by copyright. http://bjsm.bmj.com/ Br J Sports Med: first published as 10.1136/bjsports-2018-099919 on 18 October 2018. Downloaded from