Why are boys and girls born in batches?

This rule is indeed related to fertilization time. Different periods of time when semen rushes to the egg will affect the choice of sperm X chromosome and Y chromosome when it is combined with the egg during fertilization because of the fluctuation of the earth's magnetic field.

At a certain time, the Y chromosome activity is particularly high, and it is easier to combine with the X chromosome of the egg first. This will form a boy. Another time, sperm with high X chromosome activity will form girls. So at birth, the gender of the child will come together. (mainly refers to natural childbirth)