Why everyone scares of downs syndrome if a women conceives after 35? if it is real what precaution should a woman take if she conceives at 39?

Increases with age: With each passing year, the chance that a woman will have a child with downs syndrome increase. There are many women 39 (and over) who conceive children without downs, it is just more of a risk. A women who is 39 has slightly less than a 1% risk. Some people focus on that 1%, others view it as greater than 99% of women have unaffected children. Precautions won't help.

No precautions: No precautions should be taken or can be taken. If that's a true scare, she should think about not conceiving at all. Down syndrome is not preventable!