Earlier quoted context omitted.
Biologically, 40 is a bad age to have kids at. The risk of Down syndrome and other diseases increases by a lot with each passing year in the 30s and it's anyways harder to conceive. Pregnancies over 35 are considered risky and are monitored much more closely. Having kids early is problematic because of the changing economic factors: job uncertainty combined with families moving for jobs and not being able to rely on…
The thing they don’t talk about much is that age isn’t so much the factor as overall health. The two correlate pretty well, so it’s more polite to talk in terms of age, but we could watch the way my fit, active, wife was treated compared to a more sedentary, overweight, woman 10 years younger, and it was clear which one people were more concerned about. Beyond that, even assuming the official numbers are right, I was…
According to Uhl's Obstetrics and Gynaecology for example, fertility is impacted negatively for females of age > 35 and a first pregnancy over 35 or under 19 is considered a risky pregnancy. Same goes for subsequent pregnancies over 40, which have a higher risk of genetic defect, placenta insufficiency, etc.
It's perhaps interesting to note that a genetic consultation is offered to women over 35, but only to men over 50. The risk of a trisomy over 35 is 1 : 370, whereas earlier it's in the thousands and can be shrunk further through non-invasive diagnosis. There are many more things which become problematic over 35 (thrombosis, diabetes, hypertensive disorders), I don't have time to list them all, but any good book on obstetrics will have the details.
Weight issues (BMI > 25, < 19) and a sedentary lifestyle increase the risk for pre-eclampsia, pre-term birth, pregnancy diabetes or spontaneous abortion. This would explain why the lady you mentioned was likely closely monitored. It seems that some attributes of the mother (e.g. being overweight, diabetes) are also reflected in the later predisposition to disease of the child. This can include even things like natural vs. C-section birth.