Preterm birth rates among twins during the Danish COVID-19 lockdown and mitigation period

Denmark’s response to the COVID-19 pandemic was to issue guidelines on containment, isolation, and surveillance. Subsequently, Denmark entered a period with variable mitigation measures including closures of schools and workplaces, travel restrictions, and restrictions on public gatherings. A Danish study covering the lockdown period (March 12 – April 14, 2020) as well as a period of mitigation measures (February 27 – September 30, 2020) showed that the reduction in extremely preterm births was not associated with an increase in singleton stillbirth rate. Subsequent studies examining the impacts of COVID-19 mitigation measures on preterm birth have combined singleton with multifetal pregnancies. However, multifetal pregnancies have a different set of risk factors for preterm birth, as well as, increased risk of adverse outcomes, and a shorter expected pregnancy length. We assessed the impact of the Danish lockdown period, or the mitigation period on multifetal births and found no significant difference in the proportion of preterm twin births among all twin births, either within gestational age groups or in total, for either period. ### Competing Interest Statement Dr Breindahl has a patent (NeoHelp) with royalties paid. Dr Breindahl has nothing to disclose. All other authors reported to have nothing to disclose. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was conducted according to Danish legislation for register research and was approved by the Data protection Agency officer at Statens Serum Institut (No.: 20/04753) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present work are contained in the manuscript