Questions about twins?

M

So I’m curious to know how the gene is passed on. My grandmother is a twin and her mother was a twin as well. Their were 4 sets way before she was born, but her and my aunt were the last set that were born. My grandma eventually had my mom and only her. My mom went on to have me plus 3 other siblings and never got pregnant with twins. I have one child and am pregnant again with my second. I’m just curious what the likelihood of it all is. It was very interesting to find out but kind of scary!

Here’s my ultrasound btw, 4 weeks and 6 days according to the scan. We thought I was 7 weeks based off my last period.

My mil keeps bringing up that fact that I could have twins 🙃

Looks like one in their for now though?