The suboptimal methodological quality of non-Cochrane reviews on hyoscine butylbromide to shorten labour duration raises concerns about their conclusions: a meta-research study

OBJECTIVE: Hyoscine butylbromide (HBB) is commonly used off-label in labour wards. However, a Cochrane review raised concerns about the quality of evidence on HBB in childbirth, leading to the WHO's disapproval of HBB for intrapartum care. Since then, newer non-Cochrane systematic reviews on HBB to shorten labour duration have emerged. We assessed the methodological quality of these reviews to determine their trustworthiness. STUDY DESIGN AND SETTING: We critically appraised the quality of conduct for one Cochrane and seven non-Cochrane reviews with randomised controlled trials on HBB to shorten labour duration using the AMSTAR 2 tool. We also documented the features forming the inclusion and exclusion criteria to determine the overlap of the reviews regarding their inclusion criteria and identify any underreported features. RESULTS: The AMSTAR overall confidence was critically low for all non-Cochrane reviews, with more than half of the critical domains rated flawed, and moderate for the Cochrane review, since it was exemplary overall, apart from the synthesis methods. We extracted 57 characteristics referring to different features. Most reviews described the outcomes (56.1%, n=32), followed by the participant characteristics (35.1%, n=20). Intervention and comparator received the least attention. Most outcomes pertained to maternal adverse events (n=13), followed by other labour-related characteristics and neonatal adverse events in a tie (n=7), and labour duration (n=5). The coverage of the reviews regarding the reported features ranged from 10.5% to 70.2%, pointing to insufficient reporting of their inclusion criteria. We documented 30 different databases, with 19 (63.3%) also considering grey literature. The Cochrane review used 11 databases, while the non-Cochrane reviews considered 4 to 13. There was a very high overlap, especially among almost all non-Cochrane reviews, exceeding 20%. However, only a handful of the trials detected in the Cochrane review were included in the subsequent non-Cochrane reviews. CONCLUSION: Our meta-research study revealed that newer non-Cochrane reviews on HBB to shorten labour duration, published since 2019, have suboptimal methodological quality, raising concerns about the trustworthiness of their findings. The methodological quality of their included trials requires scrutiny to determine whether a future well-conducted review on HBB to shorten labour duration would add value. PLAIN LANGUAGE SUMMARY: There is an ongoing debate about the use of medical interventions for women with low-risk pregnancies. The World Health Organisation (WHO) promotes a woman-centred approach to care. This means focusing on respectful care for mothers and newborns and prioritising natural, non-medical approaches to childbirth unless a medical intervention is truly necessary. To speed up labour or help the cervix open (dilatation), many midwives and doctors use a drug called hyoscine butylbromide (HBB), which is among the frequently studied antispasmodics in medical research. Although HBB is not officially licensed for use in labour, it is a standard option in many countries, including Germany. However, since 2013, the WHO and the Cochrane review have advised against antispasmodics for labour until there is rigorous evidence to indicate that they actually help clinical practice. Since those warnings were issued, several clinical trials and systematic reviews have been published. We performed a meta-research study on published systematic reviews with clinical trials administering HBB to shorten labour. Our goal was two-fold: (i) to critically appraise the methodological quality of these new systematic reviews using a validated and well-established rating tool for systematic reviews (AMSTAR 2), and (ii) to explore if these systematic reviews were simply repeating the same data or adding new evidence. We identified seven non-Cochrane reviews published between 2019 and 2024 and compared them with the unique relevant Cochrane review published in 2013. We found that all non-Cochrane reviews had a very low methodological quality. Furthermore, almost all non-Cochrane reviews shared many of the included clinical trials; hence, they were essentially repeating the same evidence for the same research question without adding any new value. Only the Cochrane review provided evidence we could trust. The recent evidence from non-Cochrane reviews on HBB published up to 2024 should be interpreted with great caution. Midwives, doctors, and parents should be aware that the evidence for using HBB to shorten labour duration remains weak.