Asthma is the commonest chronic medical condition reported in pregnancy, affecting more than 10% of pregnant women (Flores et al., J Asthma 2020;57:693-702) and is associated with worse outcomes in pregnant women with COVID-19 and influenza. However, the quality of results that Xu et al. were able to produce, is limited. Of the 20 studies identified by the systematic review, 90% (18) were judged to have serious or critical risk of bias. For the 48 individual comparisons presented, 11 were reported in only one study, with only 9 outcomes comparable between more than three studies - these small numbers precluded the authors from incorporating any consideration as to the study quality and risk of bias into the statistical comparisons.
Maternal medicine: calling for improved research quality