Multiple births can occur either naturally (the woman ovulates multiple eggs or the fertilized egg splits into two) or as the result of infertility treatments. For reasons that are unknown, the older a woman is, the more likely she is to naturally have a multiple birth.
The number of multiple births has increased over the last few years. For example, in Canada, between 1979 and 1999, the number of multiple birth babies increased 35%. Multiple birth babies were more likely to be premature than singletons; in 1999, 53% of babies in multiple births were premature, compared to 7% of singletons. [1]
Recent increases over the last few years in the number of multiple births have also provoked concern; the greater the number of babies in a single pregnancy, the more likely they are to have a low birth weight, to be born prematurely and to consequently suffer medical problems. There is also a higher rate of stillbirths for multiples than for singletons.
Famous multiple births include: