> The authors analyzed the v-safe registry data from 14 December 2020 to 28 February 2021 (an 11- week span), which included 827 pregnancies

It's only a 11 weeks span, so if someone got a vaccine during the first trimester there are three possible outcomes:

* Induced abortion

* Spontaneous abortion

* Pregnancy not finished and not counted

So the data overestimate the number of abortions.