Hematologic Adaptation to Mask Wearing During the COVID-19 Pandemic

Background: Coronavirus disease 2019 (COVID-19) was first identified in December 2019 in China, and resulted in an ongoing pandemic. Starting at April 12, 2020, in an intent to stop the spread of the virus, Israelis were obligated to wear a face mask. Mask-wearing over the mouth and nose creates a hard-to-ventilate space which might accumulate CO2 and induce relative hypoxia, possibly facilitating substantial hematologic changes.We sought to study the association of mask wearing during the COVID-19 pandemic and hematological and obstetrical outcomes among singleton gestations. Methods: Obstetrical outcome and laboratory results of women admitted for delivery throughout the mask-wearing period were compared to those delivering during two pre-pandemic control groups- i) the parallel period in 2019 and ii) a larger cohort of pre-pandemic years (March 2011-April 2020). Findings: Overall, 1,939 women delivered during the COVID-19 pandemic. Compared with the pre-pandemic period, the mean hemoglobin and fibrinogen levels were significantly higher during the mask-wearing period [12.15±1.1 vs. 11.96±1.2, p<0.001 and 472±10 3 .6 vs. 448±85.1 (mg/dL), p<0.001, respectively]. Platelets levels were lower [200±56.0 vs. 206±57.5 (K/microL), p<0.001]. The rate of delivery<34 weeks of gestation was lower during the mask-wearing period  [1.1% vs. 2%, OR-0.57 (95% CI, 0.37-0.88), p=0.01], while cesarean delivery  and postpartum hemorrhage rates were higher [[26.7% vs. 24.4%, OR- 1.13 (95% CI, 1.02-1.25), p=0.022 and 4.1% vs. 2.8%, OR- 1.5 (95% CI 1.2-1.8), p=0.001, respectively], Conclusion: Compared to the pre-pandemic period, women delivering in the pandemic period had higher levels of hemoglobin and fibrinogen and lower levels of platelets. These hematologic changes may be the result of a hard-to-ventilate space created by wearing a mask during the COVID-19 period. It remains to be determined whether the observed lower rates of preterm birth and higher rates of postpartum hemorrhage are associated with these hematologic changes. Funding: No external funding. Declaration of Interests: The authors report no conflicts of interest. Ethics Approval Statement: Institutional review board approval was obtained for this retrospective study on March 30,2020 (# 7068-20-SMC).