 It seems like a lot of your friends are Virgos or Leos. You're not wrong. More Americans are born during this time of year than any other. So yeah, American parents are more likely to be conceiving in November and December, with August being the most common birth month and September having two of the most popular birth dates. Why? Well, scientists have theorized that sperm quality may be better during the winter, that daylight length may impact reproduction, or simply that people might just get it on more during the winter holidays. Regardless, it might not be best to think about what your parents were doing over winter break.