Objective monitoring of postpartum uterine activity: a systematic scoping review

Objective: To minimize risks of postpartum hemorrhage, understanding normal postpartum uterine activity is essential. This scoping review summarizes literature on postpartum uterine activity to provide insight into uterine activity (patho)physiology, characteristics of objective postpartum uterine monitoring methods and the effect of uterotonics on postpartum uterine activity. Data sources: A systematic search was conducted in PubMed, Embase and Cochrane in August 2024 and repeated in January 2025. No filter restrictions were applied. Systematic article selection was performed by two independent reviewers. Eligibility criteria: Articles were included if study participants were ≥ 18 years old and had external tocodynamometry (TOCO), intrauterine pressure catheter (IUPC) and/or electrohysterography (EHG) monitoring postpartum. Reviews, case reports, conference papers, technical modeling methods, guidelines, grey literature and duplicates were excluded, as were articles describing non-pregnant, non-human, non-labor studies and intrapartum studies. Study appraisal and synthesis methods: The Newcastle-Ottawa Quality Assessment Scale and the revised Cochrane risk-of-bias tool were conducted to assess study quality. Data was collected and systematically organized by two independent reviewers. Results: Twenty-nine articles were included after evaluation of 5,826 articles. Data analysis included 23 articles (IUPC n = 16, EHG n = 6 and TOCO n = 1) after risk of bias selection. Uterine contraction frequency without uterotonics ranges between 2.4 and 2.8 contractions per 10 min and between 3.7 and 4.6 contractions per 10 min with oxytocin, both decreasing over time. Normal baseline activity after childbirth is ≤ 15 mmHg and normal uterine intensity varies between 51-58 mmHg and 336-396 Montevideo Units. Studies conducted prior to 2020, measuring uterine activity with IUPC or TOCO, report no significant correlation between uterine activity and total blood loss. However, a small study using EHG conducted in 2024, cautiously suggests a positive relationship. This review highlights the need for a uniform and objective method to monitor postpartum uterine activity to adequately investigate the impact of different uterotonics on uterine activity. Conclusion: The (patho)physiology of postpartum uterine activity remains largely underexplored. EHG shows potential in enhancing our understanding of normal postpartum uterine activity as well as in postpartum hemorrhage recognition and prediction.