Spontaneous abortion or loss of the fetus before 21 weeks of gestation. Habitual abortion is defined as the spontaneous loss of 3 or more consecutive pregnancies. Habitual or recurrent abortion is a form of infertility. Couples who have had 2 or more miscarriages (spontaneous abortions) have about a 5% chance that one member of the couple is carrying a chromosome problem that is contributing to the miscarriages. A considerable proportion of pregnancies end in miscarriage.