Prenatal Diagnosis: Amniocentesis

What is Amniocentesis?

There are 46 chromosomes usually present in humans. Oocytes and sperm have 22 single autosomes and 1 sex chromosomes making 23‐to‐46 present at fertilization, but in rare cases the chromosome number will be more or less than the norm which will lead to chromosomal anomalies thus resulting in fetus abnormalities. Using fetal cells in the amniotic fluid, amniocentesis (amniotic fluid test) will examine whether there are chromosomal abnormalities in the fetus or not.

G Band Analysis

General amniocentesis uses G band analysis. By collecting and culturing fetal cells in amniotic fluid, the chromosomal forms can be identified, stained, and then observed and analyzed. Using method, we will understand the chromosome pairs 1‐22, and the sex chromosomes X and Y. Furthermore, since the chromosomes are observed one by one, we can see large anomalous partial amount or translocations (chromosome has been replaced in part). Unlike the Quattro test, to determine the probability of a particular disease, this result is a definitive diagnosis, but it will not be able to diagnose all types of chromosomal abnormalities. G band is not able to see the finer abnormalities in the analysis, because there are those small chromosomal abnormalities of microdeletion or nucleotide sequences that are the causes of congenital disease. Such congenital abnormalities have been called "Chromosome micro deletion syndrome".

羊水穿刺

Collect amniotic fluid

分裂期の胎児の細胞

Incubate fetal cells in amniotic fluid and dye mitotic cells to locate chromosomes in the nucleus.

顕微鏡で見た染色体

Observe the dyed chromosomes under a microscope to identify how many chromosomes there are. Large deletions or surpluses can be seen.
Microdeletions cannot be seen.

Chromosome micro deletion syndrome has different symptoms depending on the site of the defect (Table 1), and it is quite common to have no symptoms, but it may merge into severe symptoms. One famous example isthe DiGeorge Syndrome which has malformation of development, abnormalitiesin heart, mentalretardation accompanied by language disorder and immune deficiency, and the frequency is said to be at 1 in 4,000~5,000 people. A more accurate analysis method is needed to diagnose this syndrome.

Table 1. Chromosome Micro Deletion Syndromes

Name Deleted Chromosome Main Symptoms
Wolf‐Hirschhorn Syndrome Short arm of chromosome 4 (4p) Characteristic facial appearance, growth disorders, severe mental retardation, Hypotonia, intractable epilepsy, eating disorders
Williams Syndrome Long arm of chromosome 7 (7q11.23) Aortic valve stenosis, mental retardation, fairy‐ like facial appearance, transient Hypercalcemia in infancy
Prader ‐ Willi Syndrome Long arm of chromosome 15 from father (15q11) Decreased muscle tone from the time of birth, obesity, Hypogonadism, small hands and feet, mental retardation
Angelman Syndrome Long arm of chromosome 15 from mother (15q11) Seizures, puppet‐like ataxia, sudden laughter , flapping the hands, severe mental retardation
Miller‐Dieker Syndrome Short arm of chromosome 17 (17p13.3) Lissencephaly, low upturned nose, severe growth retardation, Seizures, severe mental retardation
DiGeorge Syndrome Long arm of chromosome 22 (22q11.21) Hypoplasia or absence of the thymus and parathyroid, Heart malformations, cleft palate, mental retardation, psychiatric problems

SNP Micro‐Array

Chromosomes are made up of protein and DNA. The DNA is bound by a double spiral to 4 kinds of bases; adenine (A), thymine (T), guanine (G), and cytosine (C), and the way the bases are arranged (base sequence) is the genetic information. The number and sequence of bases has been determined by the species, but about one in several hundred to 1,000 has a part that has a different sequence to the standard base sequence. The difference of 1 base is called a "snip" (Single Nucleotide polymorphism; SNP), it has become a product of individual differences and diversity. In the case of humans, it is said that there is “a snip” of about 10 million places in the 3 billion bases, snip related to congenital diseases have also been identified more. "SNP microarray" analyzes the base sequence of the chromosome, so we can diagnose abnormal micro chromosomes that con not be recognized by G‐band analysis.

染色体とDNA断片の図 DNA断片を増幅、ハイブリダイゼーション、解析の図 Report図
    Amplify DNA fragments

Hybridization

Analysis
  Even minute abnormalities can be determined.

To take the Amniotic Fluid Test

This is usually taken around the 17th week of pregnancy from 17 weeks 0 days ~ 3 days. For the appointment, a diagnosis of the exact number of weeks (due date) and number of fetuses will be necessary. It will be done in this order.

  • Informed Consent, Appointment
  • Make an appointment after you get the explanation. Please turn in the consent form at the time of the procedure. (If you forget, we cannot do the procedure).

  • Amniocentesis
  • Check the position of the fetus and placenta with ultrasound, and then disinfect the skin surface of the abdomen receiving the injection needle, and then collect the amniotic fluid 20 ~ 30ml located around the fetus. In this case, sometimes accompanied by pain and cervical tension, you may use a local anesthetic, if necessary. Generally it is done from 13:00pm on weekday.

  • Analysis
  • G band analysis and SNP microarray will be done at a professional laboratory. The results should be ready in 2~3 weeks due to the time necessary for the cells to be cultured.

  • Result Explanation
  • Please come in and get the results explained to you by one of our doctors. Additionally, if needed, you can receive genetic counseling from our geneticist.

Risks involved with the Amniotic Fluid Test

  • Miscarriage may occur due to amniocentesis. (Around 0.3%). In rare cases bleeding, abdominal pain, intrauterine infection, may cause complications such as amniotic fluid embolism.
  • Position of fetus and placenta, amniotic fluid volume, by maternal factors (such as adhesion of the scar and organs), and the possibility that amniocentesis cannot be done, and possibility of multiple punctures.
  • Contamination of maternal cells, culture failure, by any other unexpected cause there is a possibility that you cannot complete the test.
  • It does not mean that you can diagnose all congenital diseases by amniocentesis. If multifetal and mosaics occur (a mix of normal cells and chromosomal abnormalities), an accurate result will not be possible. In addition, there is a possibility that changes in micro chromosomes and significances are not clearly detected.
  • If the results are a normal amniocentesis, it does not guarantee the health and normal development of the child after birth.

Costs

G‐band analysis
(including amniocentesis procedure fee)
¥169,000
(With Tax: ¥185,900)
G‐band analysis + SNP microarray (including amniocentesis procedure fee) ¥269,000
(With Tax: ¥295,900)

❈Amniocentesis is not covered by insurance.
❈Prices are subject to change without notice.
❈Appointment is necessary. Please ask by phone.

English Help Desk

TEL:070-1820-0909

Email:english_help@oakclinic-group.com

【Reception time】
Tuesday~Saturday  09:00~17:00

>>Special English Help Desk Holidays