According to this New England Journal of Medicine study
829 completed pregnancies.
700 got vaccine in 3rd trimester
129 got vaccine before 3rd trimester
Out of 829 pregnancies only 129 of patients got the vaccine before the 3rd
Let us compare statistics of 1st and 2nd trimester pregnancies
So 104 spontaneous abortions (loss of pregnancies before 20 weeks) happened in 129 women who got vaccinated before the 3rd trimester