According to Jennifer Lopez’ dad she is in fact expecting twins.  The rumors have been circulating for months that the singer is expecting twins and it was later confirmed in a interview that Jennifer Lopez’s dad did with Escándalo TV.   Lopez’s dad also said that twins do run in the family. 

With the use of fertility treatment there has been a increase in multiple births.  Much of Lopez’s pregnancy has been kept private so it is not known if she did undergo fertility treatment.  Either way, older moms have an increased chance of having twins.

Source: People.com