Miscarriage

The most common cause of miscarriage is aneuploidy:

Aneuploidy is a chromosome number that is not an exact multiple of the haploid number (22 autosome chromosomes and 1 sex chromosome).  Examples are trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome), and trisomy 21 (Down syndrome.

Another reason for failed pregnancy is a hyatidiform mole, which affects placental development.  In this type of pregnancy (also called a molar pregnancy), all of its chromosomes are derived from the father.  In contrast, placental structures are absent in ovarian teratomas, tumors that contain chromosomes only from the mother.

In some fertility clinics, IVF embryos are analyzed by a technique called Polymerase Chain Reaction (PCR).  This technique amplifies small fragments of areas of DNA into quantities large enough to be analyzed.  This process makes it possible to perform DNA diagnosis from a single cell removed from IVF embryos.  This is called Pre-implantation Genetic Diagnosis (PGD).