Is three really a crowd?

I think I have baby fever.
Sydney is going to be two years old in exactly a week from today.  Madi will be 5 in just a couple of weeks.  I have tons of friends that are having babies.  It's started that thought process in me-should we have one more?
There are, of course, many reasons for and against it.  We have had a genetic panel done on Madi.  To the best of the docs' knowledge, we do not carry a gene for cardiomyopathy.  However, who knows what genes are out there that are as yet undiscovered?  That's the fear that gets to me in the darkest hours.  What if Sydney got it, too?  How would I handle that?  Do I even risk having another child after what we went through?
I know that there are a lot of people out there that say that God will provide and He wants us to go forth and multiply.  But I can't help my thinking that God also doesn't want innocent children to suffer.  I am not trying to start a religious debate here, just simply stating what's in my heart.  When I search deep inside myself I know that there probably is not a genetic component to Madi's heart disease.  I also know, when I am being totally honest with myself, that there is a part of me that would love to have another baby.  Just one more.  Not because we want to try for a boy, although I would love to have a son, but because I have this feeling that I was meant to be a mom of three children.
Our house has three bedrooms, so that would mean that eventually two little ones would have to bunk up together.  No big deal-plenty of people share rooms.  We would make it work.  I know we could.  Despite the fact that my kids test my patience and make me want to pull out my hair sometimes, the love I have for them knows no bounds.  If everyone based their decision to have more kids on their other childrens' behaviors, we would probably all be only children.  There are plenty of people out there who make it on less than we have.  I am nothing if not bargain-savvy, and I know how to stretch a buck.  We could do this.  But should we?
Some say three's a crowd, but I am not so sure.