Question

Why can both IVF and IUI result in multiple births?

Answer 1

IVF (In vitro fertilization) is a process in which egg is fertilized by sperms outside the body or in test tubes. Similarly, IUI (intrauterine insemination) is a process in which sperms are carried to the uterus to increase the chance of fertility.

Multiple births in IVF and IUI  is due to fertility drug which sometimes stimulates ovaries to produce multiple eggs which in turn result in the formation of multiple zygotes, also sperms used are washed sperms which increase the chance of fertilization of all eggs.

Also, there is a phenomenon called zygotic splitting which causes the embryo to divide resulting twins or tripplet.