Congratulations!
I totally understand your concerns and think it's definitely better to look these things in the eye now rather than later. I had my first at 39 years and am currently due my second, just after I turn 42.
I would never have let my age at this stage be a deterrent because DH and I wanted children so much and never considered it rational that just because we found each other late, and then had some fertility problems, that we therefore should not have them.
Both my parents died relatively young, so even though they had me and my siblings in their twenties, I still experienced their loss earlier than average.
Not for a second have I therefore concluded that it would have been better if I had never been born! I was loved and brought up well and those are the important things.
Also, think it's worth pointing out that although health problems are more likely to rear their ugly heads the older we get, we are not completely powerless now in terms of our health in ten, 20, 30 years. As an older mother, I have developed much better health behaviours than ever before, like getting screening done regularly, eating more healthily and getting more exercise. I know for a fact I would not be half so health-conscious if I did not really, really want to be around and healthy for as long as possible for the sake of my dd (and, all going well, ds in a couple of months!). None of us has complete control over our health of course, put as a pp pointed out, no one would expect a woman to not conceive or continue a pregnancy if she was overweight for example; things like obesity, smoking etc can have serious consequences for future health.
Didn't mean to go on so long. Just - congratulations again and this blanket attitude of 'having kids over a certain age is always a bad idea' is ill-informed and a actually bit stupid imo!