The American researcher of Harvard University, Amitabh Chandra, reports that September 16 is the day of the year when more children are born and that the 3 most crowded days of the year are: September 9, September 23, September 22. It is very rare to be born December 25 and the days that surround it. As well as in January and February 29.
1. The movement of the sun. Starting from the winter solstice, the days begin to get longer, there is what is scientifically called a reversal of the photoperiod, the hours of light increase and those of darkness decrease. From the summer solstice, the opposite will happen. So the semester from December to June is the one in which the body is more stimulated to grow, because the light stimulates the epiphysis which in turn blocks the melatonin, the substance that "sleeps" the body and blocks the sex hormones. The activity of epiphysis counteracts the action of melatonin, so it is easier to conceive. In fact, the stimulation that occurs with the lengthening of the days is so accentuated that September is the month of greatest birth.
2. Christmas holidays. The phenomenon could also be related to the holidays of Christmas, when the possibility and time to "stay in bed" is even higher.