Protocol, eligibility criteria, information sources and search
This systematic review was performed and conducted following the PRISMA30 and MOOSE31 guidelines, which were recommended standards for systematic reviews and meta‐analysis. PubMed, Embase, Web of Science and Cochrane Library were searched systematically for relevant studies from establishment until July 2021, combining relevant medical subject heading terms, key words and word variants for “hypertension” or “hypertensive” or “preeclampsia” or “preeclamptic” or “eclampsia” or “eclamptic” and “birthweight” and “discordance” or “discordant” and “twin pregnancies” (Appendix S1). The search and inclusion criteria were restricted to human data and English language. Additional reports were manually searched by two authors (YW, HYZ) according to the reference lists of selected articles and reviews.