One of the proteins that the gene therapy shots cause the body to attack is identical or very similar to a protein used in forming the human placenta. Women who are already pregnant may miscarry; others of child-bearing age will still conceive but will never develop a proper placenta, dooming the resulting embryo.
I believe you speak of Syncytin-1, which entered the genome of old world primates via infection with a retrovirus. The animals, including humans, used part of the endogenous retrovirus’ DNA for benefit. It does have some similarities to the coronavirus spike protein.
This very issue was brought forward by Pfizer’s former head of vaccine development. That was months ago.