No, please refer to the rest of the sentence:
Among 3958 participants enrolled in the v-safe pregnancy registry, 827 had a completed pregnancy, of which 115 (13.9%) were pregnancy losses and 712 (86.1%) were live births
To further clarify, the abstract of the article notes:
From December 14, 2020, to February 28, 2021, we used data from the “v-safe
after vaccination health checker” surveillance system
That is a total of 76 days.
Median human gestation is approximately 268 days. Thus, less than a third of a human gestation was covered by the study period.
Therefore it is perfectly reasonable that only 827 of 3958 (21%) participants completed their pregnancy during the study period. Presumably, some of the participants didn't fill out the survey that lets the staff know about the outcome.
Of the 827 who did have their pregnancy complete, 115 (13.9%) ended in a loss. This is consistent with previous estimates of pregnancy loss in the United States (Wilcox et al 1988. PMID 3393170).