I just want to add as someone made the point about chromosomes.

Our chronological age is different to our biological age. Many women are older biologicaly or younger biologically than they are chronologically. This is something that has been highlighted in recent years.

Statistically more children with chromosomal difficulties are born to women under 35 than over 35. Granted this can be due to the fact that women over 35 are offered routine testing by many care providers.

I have to say antecdotally I have seen in my job more women under 35 with babies diagnosed with chromosomal disorders than over 35.
There is much we don't know. But when a woman eats high quality food, supplements her diet with good quality supplements (our soil in Australia is known to be depleted in zinc and selenium to name just two), doesn't smoke, protects herself from environmental toxins and "routine chemicals" and her partner does the same her chances of having a healthy baby are huge.

Folate, b12 and b6 are proven to affect in a positive way our dna and that of our partners.

So, there is much a woman can do over 35 to help ensure a healthy baby and a healthy pregnancy...