Its a continuum. 35 or "ama" come from studies that showed that the risk of having a baby with a chromosomal abnormality was greater than the risk to the pregnancy by doing an amniocentesis after 34 years of age. The reality is that the miscarriage and Down syndrome risks increase with age, and 35 has been used just as a elineation between lower and higher risk. Diabetes, hypertension and c-section increase also.
None Specifically. Many women think 35 is a magical age for pregnancy risks but really it is not. Certainly as women get older there are higher risks of miscarriage, genetic abnormalities such as down's syndrome, and higher risks of high blood pressure, diabetes, and growth problem s in the baby. But these risks increase with each year of age and there is no specific age cutoff.