In test tube baby applications, embryos should be selected between the 2nd-5th days and transferred to the mother to be. Generally 2-5 embryos of the best quality are selected according to their appereances (morphology) and transferred. Though embryos of the best appereance are transferred; implantation and clinic pregnancy rates still have not reached the desired levels. After the pregnancy is formed, 20-25% miscarriages occur following the first 3 months. The studies conducted in recet years show that genetic disorders called aneuploidy plays an important role in the implantation of the embryos.

40-70% of the embryos obtained during test tube baby treatment show aneuploidy.Even though the transferred embryos are of good quality, it is understood that there might be a genetic disorder. Pregnancy formation possibility of a genetically unhealthy embryo is either zero (autosomal monozomy) or very low. Even if pregnancy forms, an important percentage of them result in miscarriage, and some of them result in stillbirth or babies having abnormalities.

Pre-implantation genetic diagnosis (PGD) has entered into test tube baby applications in the recent years. With PGD method genetically normal and abnormal embryos can be determined. With aneuploidy screening, numerical chromosomal defects in the embryos can be sorted. Aneuploidy screening is recommended to approximately 10% of the patient applying for test tube baby. If this 10% is applied PGD, then normal embryos are transferred and this negative course is corrected a great deal. PGD's importance in test tube baby applciaitons gradullay increases and every day more patients are recommended to receive PGD. By this way, it is aimed to increase the pregnancy possibility of couples applying for test tube baby and decrease the possibility of miscarriage.

With PGD entering into test tube baby applications, why implantation and pregnancy rates are low is partially revealed. With this method 40% genetic defects are detemined even in embryos seemed to have good quality and 90% in embryos of bad qualityTherefore, seemed to be of good quality however, genetically abnormal embryos have a low chance of forming pregnancy, and even if pregnancy is formed, the possibility to end in miscarriage is quiet high. If the pregnancy does not result in miscarriage, then a genetically diseased baby will be born.

Couples who have no problem in conceiving but carriers of genetic diseases can have the opportunity to have a healthy baby with PGD method. This kind of patients usually applies with the history of recurrent miscarriage, stillbirth, and abnormal baby. Some of the couples having known to be carriers of this kind of genetic diseases apply for assistance before any attempt to conceive. In single gene disease or translocation carriers, obtaining a healthy pregnancy is achieved with PGD without taking chances.