How common is it for an infertile couple to adopt and then end up having biological children?

Hello everyone,,
So whenever I tell people my “story” - that my parents tried for nearly a decade to have kids before adopting me and then went on to have two biological kids - people always reply that it’s super common, that they know someone this happened to, that the woman’s “mothering” hormones kicked in and she was able to get pregnant, etc.

My mom had very, very difficult pregnancies and births with my siblings and I can’t help but think that was been related to whatever caused her infertility. This happened in the eighties so I don’t know that there was a cause ever determined for my parents infertility issues.

It’s just made me curious about how common this actually is and how many of you know of or are involved in similar situations? If it is true, is there anything scientific that’s been found to cause it?

Edit: thanks to all the adoptive and potential adoptive parents who shared their experiences with this. Thank you for opening my eyes to how hurtful it can be to have people make statements like “well hopefully once you adopt you’ll have a bio kid” and so on.....

i think it is true because i have an aunt and for 10yrs nothing happens so they adopted her niece (just after birth) on her husband side. miracles happens that after 2 years she finally got pregnant and it continued for 3 more times until my uncle finally wear a condom. the reason is probably because the stress on both them of not having a baby is gone so their reproductive system probably relaxes or their brain is not thinking too much on that baby making so it somehow reset.