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Evaluation of invasive prenatal diagnosis

Date:2017-01-05

Prenatal diagnosis, also known as intrauterine diagnosis, is a discipline closely related to cytogenetics, molecular genetics, biochemistry and medical practice. In the mid-1950s, amniocentesis was first applied to the clinical identification of fetal sex and fetal hemolytic disease diagnosis. In the ensuing decades, the continuous development of ultrasound imaging technology, the early pregnancy villus biopsy and intrauterine blood collection technology and the advent of the development of molecular biology technology, so that prenatal diagnosis of fetal prenatal diagnosis has been a breakthrough progress. At present, the clinical application and its value of the commonly used invasive methods of prenatal diagnosis (villus biopsy, amniocentesis and umbilical cord blood aspiration) are mainly evaluated.

 
First, villus biopsy:

      Chorionic Villi Sampling (CVS) is considered as an important breakthrough in prenatal diagnosis since the villus tissue is located outside the embryo sac and has the same heredity as the embryo. Since 1975, China's Anshan Iron and Steel Hospital Obstetrics and Gynecology first Reported a successful vaginal biopsy performed by cervical aspiration fetal sex prediction in 1983, Simoni villus tissue successfully performed fetal karyotype analysis, the technology began to be widely used in prenatal diagnosis of fetal genetic diseases .

    (A) on the indications:

            1. Elderly pregnant women: pregnant women over the age of 35 have a higher chance of chromosomal non-separation than normal, such as birth trisomy 21 children 25-35 years of age was 0.15% over the age of 35 for 1% -2%. 40% up to 3% -4%. It is therefore commonly accepted that prenatal genetic diagnoses should be performed for pregnant women> 35 years of age.

            2. Have had a history of children with chromosomal abnormalities: any child who has had a chromosomal abnormalities, the chance of having such children again fertility is 1/60, more than 10 times larger than normal pregnant women. Therefore, such pregnant women should be prenatal diagnosis of pregnancy again.

            3. One of the couples is a chromosomally balanced translocation carrier or inversions: congenital stupid 2% -3% is a chromosomal translocation type, the probability of such balance translocation parents birth innocence was 33%. However, in fact, if the father is in equilibrium with a translocation, the risk of having a child born is 2% -3%. For example, the risk of the mother being a balanced translocation is 10%. The reason why the actual figure is lower than the theoretical figure is related to the inability of some abnormal gametes to survive.

           4. Pregnant women with a fragile X syndrome family: Fragile X syndrome (FraX) is the most prevalent in the X-linked mental retardation syndrome. It is linked to the brittle point on the X chromosome.

           5. One of the couples is a certain kind of single-gene disease, or have had a single-gene disease in pregnant women. The genetic pattern of single gene disease is in accordance with Mendel's law, so the risk of having a sick child can be predicted.

           6. There are unexplained natural abortion history, teratogenic history, stillbirth or neonatal death of pregnant women.

     (B) on the sampling time:

        Most advocates during the 9-11 weeks of pregnancy. As early as this period, the placenta villus too thin, it is difficult under ultrasound to decouple the tissue surrounding it, but not easy to obtain villous tissue. There are also reports that premature villus biopsy may lead to fetal acromegaly risk. However, due to the rapid development of the embryo 11 weeks after pregnancy, it is difficult for the villus biopsy catheter to enter the placenta attachment site. However, the transabdominal villi biopsy is not limited by the development of pregnancy.

     (C) on the amount of villus biopsy:

        The amount of tissue required for different diagnostic purposes varies from about 10 mg of chorionic villus to 5 mg of villus DNA, while biochemical assays require only 3-5 mg of tissue. So a villus biopsy to obtain about 20mg villi tissue to meet the needs of any prenatal diagnosis.      

     (D) on the villus sampling ways and methods of operation:

        Early pregnancy villus biopsy can be taken by the cervical CVS, CVS by the CVS and vaginal vault CVS three ways. Cervical villi biopsy specimens may occur contamination, infection of the fetus or maternal and inconvenient shortcomings, since the late 1980s in the ultrasound-guided percutaneous villus biopsy technology come out. The method effectively prevents specimen contamination and possible infection. And abdominal puncture easy to reach the placental villus, not prone to the risk caused by the cervical route. At present, this method has gradually replaced the via villus biopsy. Methods: The pregnant women emptying the bladder, supine position, preoperative B supernormal observation of embryonic development, measuring the length of the buttocks to check the gestational age, location of placental villi. Abdominal routine disinfection, in exchange for disinfection and puncture probe selection puncture point and angle, using bi-needle biopsy needle technology. The bi-needle biopsy system consists of a 18-gauge guide trocar with a length of 15 cm and an outer diameter of 1.2 mm and a biopsy needle No. 22 of 20 cm and an outer diameter of 0.8 mm. Under the guidance of ultrasound, guide the trocar first through the abdominal wall and uterus into the placenta villus edge part, pull out the needle core, and then biopsy needle into the placenta through the guide tube villus tissue, connected with 2-4ml saline 20ml Syringe, 10-15ml negative pressure to move the biopsy needle up and down villi tissue. Immediately after pulling the needle to observe the placental site bleeding and fetal heart conditions. If the volume of biopsy is not enough, the biopsy needle can be introduced into the guide trocar again for aspiration until the desired amount of villus specimen is obtained.

      (E) on the safety and feasibility:

       The incidence of miscarriage after CVS and biopsy-induced fetal limb development disorder is the most concern. Reported in the literature, compared with the amniocentesis during pregnancy, CVS increase the risk of abortion up to 1%. However, there is still controversy about CVB leading to Limb Reduction Defects (LRD). Firth (1991) has followed 539 pregnancies 56-66 days after villus biopsy pregnancy outcomes, including 5 cases of LRD, that early villus biopsy can lead to fetal limb development disorders. However, Smith-Jensen et al. (1992) concluded that CVS did not increase the incidence of LRD in fetuses when pregnancy outcomes were observed after 9-12 week old villus biopsies. To this end, WHO conducted a long-term, multicentre surveillance of CVS safety issues and found that 115 out of 216,381 CVS developed LRD, with an incidence of 1 in 1881, whereas in controls the LRD The incidence was 1/1642, there was no significant difference between the two groups; CVS group, the incidence of transected LRD was 44.3%, while the control group, the incidence was 42.7%, the two nor statistical differences; different gestational cycles The incidence of LRD was no significant difference between CVS group and normal control group. Therefore, the WHO believes that CVS in early pregnancy is a safe and reliable prenatal diagnostic technique (WHO / PAHO, 1999).

     The principle of prenatal diagnosis should be as early as possible to make a diagnosis and may adopt a safe interventional prenatal diagnosis. In 1990 after the gradual elimination of foreign cervical CVS, the implementation of B-guided abdominal CVS. Burn et al 10741 cases of TA-CVS were analyzed, the fetal loss rate was 1.64%, the average amount of material was 15.2mg, puncture failure rate was 0.19%, maternal tissue contamination rate of less than 1%, due to lack of material can not lead to prenatal diagnosis (0.1%), they suggest that transabdominal CVS is a safe and feasible interventional prenatal diagnosis (Prenat Diagn 2003; 23: 295-301). Philip and so on 1914 were performed via abdominal CVS and 1861 early pregnancy sheep 77-104 days of pregnant women were randomized in pregnant women with normal fetal karyotype, fetal CVS fetal loss rate was 2.1%, early sheep There was no significant difference in the rate of fetal loss in the weaning group (2.3%), but in the 13-week-old pregnant women, the incidence of fetal callalrinis was 0.76% in the early goat weaning group and 0.16% in the CVS group The difference was statistically significant (P = 0.07), while the general population was 0.1-0.3% (Obstet Gynecol 2004; 103: 1164-73). Papp and other 15-year CVS summed up the experience of the operation-related cervical CVS group, fetal loss was 4.8%, while 1.7% of the CVS group, so that early pregnancy interventional prenatal diagnosis should be preferred abdominal CVS (Fetal Diagn Ther, 2002; 17: 218-27). Beijing Union Medical College Hospital obstetrics and gynecology from January 2000 to April 2004 220 pregnant women during the first trimester of pregnancy under the guidance of B ultrasound using double-needle cannulation catheter ablation of prenatal diagnosis, 220 cases average age of 32.04 years, both For singleton pregnancy, the extraction time of 9-14 weeks, an average of 10.67 weeks, the average amount of material was 17.1mg, puncture success rate of 100%, the operation-related spontaneous abortion rate was only 0.46%, no case of maternal tissue contamination. The results also showed that pregnancy after 9 weeks underwent B-guided transvaginal villus harvest is a safe and feasible method of interventional prenatal diagnosis of early pregnancy (Chinese Journal of Obstetrics and Gynecology, 2005). 
Second, amniocentesis:

      Amniocentesis is the most commonly used invasive prenatal diagnostic technique. This technique was first used in clinical diagnosis of fetal identification and fetal hemolytic disease as early as the 1950s. 1966 Steele and Breg successfully carried out amniotic fluid cell culture and fetal karyotype analysis, amniocentesis is widely used in prenatal diagnosis of fetal chromosomal diseases and congenital metabolic diseases (Qi Qingwei, Ge Mingying, 2000). The main source of amniotic fluid for fetal urine, tracheal bronchial secretions, amniotic epithelial secretions and maternal serum placental exudate. Amniotic fluid volume increases with gestational age, pregnancy 38 weeks up to about 1 liter, after a slight decrease in the 15-16 weeks of pregnancy when about 180-200ml, this time the uterus has been beyond the pelvis, and amniotic fluid in a high proportion of living cells, Is considered the best period of amniocentesis, and at this time amniotic fluid puncture volume can be about 20ml. Foreign authors have reported that 9-13 weeks of gestation early amniocentesis for prenatal diagnosis, can also be similar to the effect of the second trimester amniocentesis. Early amniotic fluid taken by the amniotic fluid volume varies according to different gestational age requirements are generally believed that during pregnancy 7-10 weeks, the safety of amniotic fluid intake of 5ml, pregnant 10 weeks after the extraction of amniotic fluid up to 10ml above.

      Prior to amniocentesis, the placenta and amniotic fluid should be located by ultrasound and the situation of the placenta should be fully understood. The puncture needle should avoid the placenta and fetus. Amniocentesis is a safer, prenatal diagnostic technique with associated abortion rates of 0.5%, even with postoperative abdominal pain, infection or water leakage (Cranda, 1994). In a controlled study of 3910 cases of amniocentesis, the abortion rate was 2.1% in the puncture group compared with 1.5% in the control group, but with the exception of vaginal bleeding itself that could cause miscarriage, the abortion rate in the puncture group was Only 0.03% more than the control group, with no statistical significance (Antsaklis, 2000).

      Amniotic fluid cells contain different types of tissue cells, including fetal kidney cells and fetal epithelial cells. Amniotic fluid cell culture, amniotic fluid cells in the natural growth of cell populations, cells were epithelial or fibroblast-like. In the past, amniotic fluid cell culture chromosome preparation common culture flask method, generally need to cultivate about 12 days before cell harvesting, the most commonly used method is cover glass method, just 1 week or so to harvest cells (Hao Na, 2002). 
Third, percutaneous umbilical vascular puncture:

        With the development of perinatal medicine, fetus blood samples for a variety of measurements to understand whether the fetus has birth defects and assess the status of the fetus in the uterus is an important prenatal diagnosis of progress. Valenti was the first to use a modified pediatric cystoscope in 1972 to perform a hysterectomy insertion in the amniotic cavity of a medium-term pregnancy, successfully obtaining fetal umbilical cord blood samples. In 1979, Rodeck and Campell applied fetal lens to umbilical vascular puncture, which brought a breakthrough in fetal intrauterine blood collection. However, due to the high incidence of complications and its application is limited. The development of high resolution ultrasound technology makes the umbilical umbilical blood vessels image very clear. In 1983, Daffos first reported the ultrasound guided cordocentesis (Cordocentesis), and then began to be widely used in the prenatal diagnosis of fetal diseases.

     (A) on the indications:

         1. Rapid Karyotyping: Fetal Blood Cell Culture Chromosome preparation takes only 48 hours to diagnose pseudo-chimerism in villi and amniotic fluid cultures or to correct or remedy failed cultures, especially amniotic fluid in the diagnosis of fragile X syndrome Villus check unmatched.

        2. Fetal intrauterine infection diagnosis: Fetal blood serum-specific IgM antibodies can be detected in TORCH pathogens intrauterine infection, but the fetus immune system to 21-22 weeks to mature and function, so the determination of fetal immune antibody Should be carried out after 22 weeks of pregnancy. With the development of molecular biology technology, the application of PCR to amplify pathogen DNA or RNA for diagnosis of various infections will not be limited by gestational age.

        3. Prenatal diagnosis and risk assessment of fetal hematologic disorders: hemolytic anemia, autoimmune thrombocytopenic purpura, hemophilia, and alpha, beta thalassemia.

        4. Intrauterine growth retardation (IUGR) monitoring and assessment of intrauterine conditions.

        5. Umbilical cord blood transplants can be used to treat intrauterine transfusion of fetal hemolytic anemia

      (B) on the puncture time and blood volume:

        Umbilical cord blood puncture in pregnancy 18 weeks to full-term pregnancy can be carried out. If less than 18 gestational weeks, the diameter of the umbilical cord more than 0.5cm, puncture more difficult. On the contrary, although the umbilical cord in the second trimester relatively coarse puncture relatively easy. But for the placenta located in the posterior wall, fetal body will often prevent the needle from entering and not easy to puncture success. At present, 20-24 weeks of pregnancy as the best time to puncture. Generally believed that about 20 weeks of pregnancy blood volume up to 6-8ml, no effect on fetal circulation, and can be repeated.

      (C) on the complication:

          The main complications of umbilical venipuncture puncture site bleeding, umbilical cord hematoma, transient fetal heart rate reduction, infection and miscarriage or fetal death. Most complications are transient and non-fatal, while the associated fetal abortion rate is about 1% -2%.

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