40 and pregnant with #4, worried

I'm going to be 40 in May. Just found out I'm pregnant with baby #4. I have a 15yr old and twin 11yr olds. My husband wants us to get rid of it. He has made some really good points and reasons why and I agree 100% with everything he is saying but there is something holding me back wanting to continue with the pregnancy. After the twins were born at 28weeks, I've always had a hole. I didn't get to finish the pregnancy with them and a decade later I still feel unfinished. But this can't be the only reason to bring another life into the world. Honestly, I don't have a good reason for having a 4th baby. So why can't I come to terms and end the pregnancy? It's still early stages where I would feel comfortable doing it but it's now or never. I don't know what to do. What if I end up with twins again, what if because of my age it has health issues, what if, what if....