On Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons

To the Editor: Shimabukuro et al. (June 17 issue) 1 reported preliminary data on the safety of messenger RNA (mRNA) Covid-19 vaccines in pregnancy from the v-safe surveillance system and pregnancy registry. They reported that among 827 participants with a completed pregnancy, the pregnancy resulted in spontaneous abortion by week 20 in 104 (12.6%), and the authors indicated that this proportion was similar to that in the general population. This calculated metric is misleading and does not reflect the real risk of spontaneous abortion. As stated in the article, among the 827 participants with a completed pregnancy, 700 received their first . . .