What's the difference between PGD, PGS and PGH? What technologies are there? Preimplantation genetic diagnosis is mainly used to check whether embryos carry genes with genetic defects. After sperm and eggs combine to form fertilized eggs and develop into embryos, PGD technology is used to detect genes before implantation in uterus, so that IVF can avoid some genetic diseases. At present, preimplantation genetic diagnosis has been able to diagnose some monogenic diseases, such as hereditary deafness and polycystic kidney disease.
Pre-implantation genetic screening, before embryo implantation, PGS is used to detect the chromosome number and structural abnormality of early embryos, mainly to detect whether the chromosome structure and number of embryos are normal.
In order to make non-professionals better understand PGD/PGS, we might as well make an image metaphor. Normal human cells have 46 chromosomes, compared to 46 pearl necklaces. There are many genes (tens of thousands in total) on each chromosome, which is compared to pearls on a necklace. Whether the number of necklaces (chromosomes) is normal or not determines whether an individual can survive or have chromosomal genetic diseases; Whether pearls (genes) are normal or not determines whether monogenic genetic diseases occur. PGD is like the owner of a jewelry store. It focuses on whether every pearl has flaws. PGS is like a security guard in a jewelry store. Its duty is just to keep an eye on these 46 necklaces to see if there is one more or one less. Sometimes it can be seen whether a necklace is obviously missing or missing (large fragments are repeated or missing). As for the state of a pearl, that is not its duty.
PGD/PGS are both embryo screening/diagnosis techniques that require very high laboratory requirements. At present, China has successfully transplanted healthy embryos by using PGD/PGS technology, so that many expectant mothers who suffer from monogenic diseases or have multiple abortions in the elderly have healthy babies.
When do you need PGD/PGS? During in vitro fertilization, doctors use hormones to stimulate women's ovaries. The ovary produces multiple eggs, which can then be extracted manually by reproductive experts. In the laboratory, experts use sperm from partners or donors to fertilize female eggs and create embryos. However, it is not easy to choose healthy and energetic embryos for implantation, which requires studying the genetic material of embryos to detect whether there are some genetic changes in embryos.
When a couple knows that one or two of them are carriers of a genetic disease, or that someone in the family has a genetic disease, or that they already have a sick child, they can use this technology in in vitro fertilization combined with embryo transfer. This is different from the traditional prenatal diagnosis methods, such as ultrasound and amniocentesis, which are pregnancy first and then diagnosis. Screening is carried out in the embryonic period, that is, the diagnosis is made before pregnancy.
At present, the application of PGD mainly focuses on ten monogenic diseases, including autosomal recessive diseases, such as thalassemia, cystic fibrosis, spinal muscular dystrophy, sickle cell anemia, autosomal dominant diseases, such as Huntington's disease, myotonic dystrophy and peroneal muscular dystrophy, and sex-linked diseases, including fragile X chromosome syndrome, progressive muscular dystrophy and hemophilia. Most of these diseases are applied to patients with definite genetic defects.
In addition, PGS is suitable for infertility caused by old age (> 35 years old), previous aneuploid pregnancy, repeated in vitro fertilization (IVF) failure, repeated abortion, severe male infertility and other factors.
The main process of PGD/PGS is indication evaluation → routine examination in reproductive clinics of both parties before treatment → determination of infertility reasons, informing of the need for PGD and selection of treatment scheme → necessary auxiliary examination and evaluation → checking relevant documents and signing informed consent → entering the treatment cycle of in vitro fertilization-embryo transfer → adopting FISH, array-CGH or gene sequencing technology → selecting normal embryo transfer according to test results and embryo development → follow-up of pregnancy outcome → pregnancy management. For details, please consult the medical staff of Reproductive Medicine Center.
The main contraindication of PGD/PDS is 1, and it suffers from diseases that are not suitable for childbearing as stipulated in the Law on Maternal and Child Health Care. 2. Suffering from diseases stipulated in the Maternal and Infant Health Care Law and currently unable to perform PGD/PGS; 3. One of the men and women suffers from serious mental illness, acute infection of urogenital system or sexually transmitted diseases; 4. Couples with other IVF-ET contraindications. For couples who need PGD/PDS, they should first go to the reproductive medicine center to evaluate the indications. Both husband and wife should do routine examination before treatment to determine the cause of infertility and then choose the appropriate treatment plan, and then carry out the subsequent corresponding procedures.
Will PGD/PGS greatly improve the implantation rate and survival rate of embryo transfer? Experts say this: "More than 50% of abortions are caused by chromosomal abnormalities. Women under the age of 30 are morphologically high-quality embryos, but about 30% of women still have chromosomal abnormalities through biopsy. Therefore, we still suggest to be the third generation IVF if conditions permit. If these patients do not have a monogenic genetic disease such as polycystic kidney disease, they should do PGS, that is, chromosome screening. After screening, embryos with normal chromosomes are selected for transplantation, such as our most common 2 1 trisomy with abnormal chromosome number, commonly known as Tang Bao. Therefore, with the emergence of the third generation of IVF, this technology is not only helpful for the diagnosis of single-gene genetic diseases before implantation, but also of great significance to elderly patients who have failed to transplant many times.
Although PGD and PGS can avoid induced abortion or induced labor caused by routine prenatal diagnosis, there are still many problems worthy of attention in practical clinical application. PGD and PGS were finally diagnosed by invasive surgery on embryos, and their offspring need long-term follow-up of large samples.