What Is a Prenatal Clinic?

Except for early and second trimester miscarriages and fetal death, about 3-5% of babies born have physical or mental impairments. Congenital defects account for 20-25% of all perinatal deaths. In the past, those couples who were at high risk of genetic abnormalities were often in a passive situation with no choice for the birth of healthy offspring. Until 1966, scholars discovered the correlation between advanced maternal age and Down's syndrome. Since then, prenatal diagnosis has developed rapidly.

Ma Jingmei

(Attending physician)

Department of Obstetrics and Gynecology, Peking University First Hospital

Prenatal diagnosis refers to the detection and diagnosis of the developmental status of the embryo or fetus and whether it has a disease before birth. So as to grasp the opportunity, for the curable diseases, choose the appropriate time for intrauterine treatment; for incurable diseases, can make informed choices. The generalized prenatal diagnosis includes: recurrent spontaneous abortion during early pregnancy; history of previous birth defects; family molecular genetic history; family history of neural tube defects; pregnancy with type 1 diabetes, hypertension, epilepsy, asthma; previous exposure to drugs, viruses, Environmental hazards; parents close relatives.

Chinese name: Prenatal diagnosis

Foreign name: prenatal diagnosis

Prenatal diagnosis history

Down syndrome (trisomy 21 syndrome) is the most common of all babies with chromosomal abnormalities. Therefore, prenatal diagnosis in the narrow sense is only for diseases with abnormal fetal chromosome numbers or structural abnormalities. During pregnancy, invasive diagnostic methods (villus removal, amniocentesis, and percutaneous umbilical puncture) are used to obtain fetal-derived cells for chromosomes Karyotype test, found and confirmed, can terminate pregnancy as early as possible before delivery.

Because this diagnostic method has material-related complications such as abortion, for large-scale populations, screening methods are used to identify high-risk populations and then invasive prenatal diagnosis is adopted. This strategy is consistent with the principles of health economics.

Prenatal screening in China was relatively late. Until 1998, foreign databases and risk value calculation software were gradually introduced. After China formally formulated the "Administrative Measures for Prenatal Diagnosis Technology" in 2002, localities have successively approved the establishment of prenatal diagnostic institutions to gradually standardize the second trimester serological screening to detect the high risk of trisomy 21, trisomy 18, and neural tube defects. Population, and then perform prenatal diagnosis.

Purpose of prenatal diagnosis

The purpose of prenatal diagnosis is not limited to finding abnormalities before birth to terminate pregnancy. In fact, prenatal diagnosis includes the following purposes:

1. To enable doctors to take prenatal or postnatal diagnosis of fetal or neonatal medicine or surgery at the appropriate time before or after birth.

2. Parents can understand the pregnancy status and then make informed choices.

3. After the parents are informed, they have the opportunity to prepare psychologically, socially, economically, and medically, and to face possible intrauterine or neonatal health problems.

Prenatal diagnosis object

Based on the "Prenatal Diagnosis Technical Standards for Cytogenetics of Fetal Chromosomal Abnormalities" introduced by the Ministry of Health of China in 2010, only in terms of cytogenetics, the indications for prenatal diagnosis include: 1.13 pregnant women over 1.35 years old; 2. Pregnant women who are at high risk of fetal chromosomal abnormalities; 3. pregnant women who have had children with chromosomal diseases; 4. prenatal B-ultrasound pregnant women who suspect that the fetus may have chromosomal abnormalities; 5. one of the couples is a carrier of chromosomal abnormalities; 6. Other conditions that the doctor considers necessary for prenatal diagnosis. ^[1]

In addition, generalized prenatal diagnosis should also include: recurrent spontaneous abortion during early pregnancy; history of previous birth defects; family molecular genetic history; family history of neural tube defects; pregnancy with type 1 diabetes, hypertension, epilepsy, asthma; previous exposure to Drugs, viruses, environmental hazards; close parents.

Prenatal diagnosis methods and scope

Invasive prenatal diagnosis

Amniocentesis (Amniocentesis)

Mostly used for prenatal diagnosis of chromosomal abnormalities. At 16-22 weeks of pregnancy, 10-20ml of amniotic fluid is drawn under the guidance of ultrasound. Because amniotic fluid is rich in fetal exfoliated cells, it can be used for the detection of the following items.

1) Down Syndrome (Trisomy 21)

Also known as congenital fool type, that is, the number of chromosome 21 is not two, but three. The reason is that one of the children's parents, during the process of germ cell formation, meiosis is caused by chromosome 21 is not separated, and abnormal gametes are combined with normal gametes. As older women over 35 years of age increase with age, this probability increases significantly, so over 35 years of age is one of the indications for prenatal diagnosis.

Typical symptoms include severe mental retardation, small head, low muscle tone, and specific facial features (wide eye distance, upslope of the outer corner of the eye, crusts of the inner palate, low root of the nose, frequent mouth opening, tongue extension, and drooling). Ears are low or deformed. The occipital bone is flat, the posterior cyanosis is low, the neck is short and wide, and the webbed neck is short. The maxillary development is poor, the zygomatic arch is high, short and narrow. Congenital heart disease (most common is ventricular septal defect). The hand is short and wide, with the fifth finger flexed radially. Specific skin texture. Males have short penis, cryptorchidism, and small scrotum. Some patients have a congenital megacolon.

2) Trisomy 18 (Edward's syndrome)

Most are produced by meiosis of parental germ cells without separation. It is manifested as: retarded growth and development before and after birth, low birth weight, poor sucking ability, difficult feeding, mental retardation, small and long head, and occipital bulge. Eyes are wide and the inner skin is thick. The nostrils are facing the sky and the ears are low. Short neck and loose skin. 90% have congenital heart disease (ventricular septal defect, open ductus, etc.). Small jaw. Infants and young children have low muscle tone and thereafter become hyperactive. Vulvar deformities (male cryptorchidism, female clitoris and labia majora, perineal abnormalities)

The prognosis is very poor, 95% of abortions in the fetus, and one-third of children born will die within one month after birth. 50% died two months after birth.

3) Turner's syndrome

Also known as congenital ovarian dysplasia syndrome, female gonadal dysplasia. One X chromosome is missing from normal women, causing related clinical symptoms, including primary amenorrhea, webbed neck, elbow eversion, and short stature.

4) Intrauterine infection detection (such as Cytomegavirus, CMV, through the virus culture of amniotic fluid, PCR detection to determine whether there is a fetal infection.)

5) Decompression when there is too much amniotic fluid. ^[2]

Villus sampling (CVS)

In the early pregnancy, a small amount of villi is extracted through the yin or abdomen through ultrasound guidance. Because the villi constitute fetal cells that contain the outer trophoblast, it is better than amniocentesis during mid-pregnancy. The advantage is that if early pregnancy screening indicates chromosomal abnormalities, Such as Down syndrome (trisomy 21) (Down Syndrome), trisomy 18 (Edward's syndrome), Turner's syndrome (Turner's syndrome). CVS can be detected and diagnosed as early as possible, on the one hand, it can greatly relieve the stress of pregnant women, on the other hand, if the pregnancy needs to be terminated, the damage is small.

The disadvantage of this method is that the risk of miscarriage associated with surgery is relatively high, reaching 2-3%. In addition, if performed before the 9th week of pregnancy, limb abnormalities may occur. Therefore, it is usually carried out after 11 weeks.

Other problems include: Maternal Cell Contamination.

But at this time, neural tube defects and other structural abnormalities cannot be diagnosed.

Percutaneous umbilical puncture (Cordocentesis)

In addition to diagnosing chromosomal abnormalities, it can also be used for the treatment of Rh allografts.

4 Pre-implatation genetic diagnosis

5. Fetoscopy ^[3]

Non-invasive prenatal diagnosis

Ultrasound

It can be used to evaluate the gestational age, determine the gender of intrauterine pregnancy, placental location, determine multiple pregnancies, and discover structural abnormalities related to chromosomes, metabolism, and molecular genetics.

Rapid prenatal diagnosis

Due to the traditional chromosome analysis of fetal cells, it is necessary to culture the collected fetal cells. It usually takes 7-10 days to harvest and analyze the cells in the middle stage of division. The work process is relatively complicated, and there are certain requirements for staff qualifications, so it takes a long time from material collection to reporting. At present, the industry norms of the Ministry of Health of China require 28 working days to issue a report, which brings greater harm to pregnant women and their families waiting for results. Distress, a long time in a more anxious state, rapid prenatal diagnosis came into being. ^[4]

Rapid prenatal diagnosis does not require culture. For interim fetal cells, the operation and reading process is relatively simple, greatly reducing the reporting time. But the more commonly used methods include:

Fluorescence in situ hybridization-based technology (FISH)

FISH

Primer in situ labeling (PRINS)

Comparative Genomic Hybridization (CGH)

Spectral Karyotype Analysis (SKY)

Microarray-Comparative Genomic Hybridization (Array-CGH)

PCR-based technology

Real-time quantitative PCR technology (QF-PCR)

Multiplex Dependent Probe Amplification Technology (MLPA)

Digital PCR technology ^[5]