My mother-in-law suspects that my child is not my son but her son’s brother. I’ve decided to clear things up, even though it’s embarrassing for me

My husband and I have been together since we were 16 years old. We went to the same school, though in different classes. We’ve been together for 10 years now, but our love hasn’t changed even slightly. We’ve had a complicated relationship with my mother-in-law, and she’s never liked me. Luckily, my husband and I live separately from his parents, and I rarely see my mother-in-law. My relationship with my father-in-law, Semen Viktorovich, is a different story. I call him Dad, and he calls me his daughter.
It didn’t start this way, but things were fine at the beginning. This isn’t the only problem in our family life. We’ve been trying to have children for a long time, but no matter how hard we try, my body couldn’t carry a pregnancy. However, we dreamed of having a child more than anything in the world. We were advised to try IVF (in vitro fertilization).
I became pregnant through IVF once, but sadly, I had a miscarriage at an early stage. I don’t want to dwell on that now because I’m still not over it. About half a year later, circumstances led to my husband, Andriy, having to work in another city for a week. During his absence, my father-in-law, Semen Viktorovich, moved in with us temporarily because he knew that I worked a lot and often came home exhausted. Especially in my state, being alone at home made me not want to cook. Semen Viktorovich helped me with household chores like cooking, starting the washing machine, and doing the dishes, without me asking him to do so. When Andriy returned, we received some wonderful news: I was expecting a child. My happiness knew no bounds. I walked around with the widest smile on my face, and both Andriy and Semen Viktorovich shared in my joy.
However, my mother-in-law reacted to the news quite coldly. The pregnancy was difficult for both me and our son, Viktor. But that was insignificant to me. I left the hospital happy with my son in my arms. When we returned home, Andriy’s parents welcomed us. My mother-in-law even hugged me and cradled her grandson in her arms. Semen Viktorovich was jumping for joy all day. However, the next day, my mother-in-law returned to her usual self, but we didn’t pay much attention to her. Time passed, and we decided to celebrate the New Year at Andriy’s parents’ house. While sitting at the table, everyone was joyful except my mother-in-law. She was sitting across from me, giving me and my son, Viktor, a cold look.
“Only a blind person wouldn’t notice the resemblance between Viktor and his grandfather,” she said, unable to hold back. Apparently, she had calculated the dates and drew her conclusions. Her arguments were quite compelling: I couldn’t get pregnant from my husband, but as soon as he left, it happened. Moreover, Semen Viktorovich inexplicably lived with me during that time. Of course, no one took her words seriously.
I won’t even mention the arguments and quarrels that followed her statement. After talking to my husband and my son, my mother-in-law seemed to calm down, but she still looks at her grandson with the same disdain as before. Soon, I will take a DNA test. It’s humiliating for me, but it’s the only way to put these doubts to rest.