How does prenatal care help a baby to be born healthy with no birth defects?

I'm thinking about some doentaries and photos I've seen from India, mostly places in the east or in underdeveloped countries. They seem to have an extraordinarily high amount of babies born with birth defects. Is this because many of them don't receive prenatal care? If so, how does prenatal care prevent babies from being born, for example, with mermaid syndrome, or wolfman syndrome, or the elephant man syndrome. I would think that such birth defects would be hard-wired into the DNA, and no amount of prenatal care could avoid it. On the other hand, I'm aware that prenatal vitamins and a healthy lifestyle with nutritious foods and physical exercise (and good genes too) will most likely pave the way to a healthy, whole child being born.