Under what circumstances will two healthy couples give birth to Down's baby?

Normal couples will also give birth to Down's children, because during the meiosis of sperm and eggs, there may be a problem of 2 1 trisomy. Relatively speaking, the older a pregnant woman is, the greater the chance of giving birth to a Down's baby in the future. Therefore, all pregnant women should routinely do Down's screening to avoid giving birth to Down's babies in the future.