amnio

Amniocentesis

Amniocentesis is the withdrawal of amniotic fluid from around the fetus. A slender needle is inserted into the woman's abdomen and into the uterus. About an ounce (2 Tablespoons) of amniotic fluid is taken out.

There are many reasons for amniocentesis. Certain women have a greater than average chance of giving birth to an infant with a chromosome problem. For instance, if you are 35 years old or older, amniocentesis may be offered to you. You are also at risk if you have already had a child with a genetic disorder or a neural tube defect -- the improper development of the brain or spinal cord. You and your care provider should decide whether the information yielded by the amniocentesis is important enough to warrant having the procedure done. For genetic reasons, amniocentesis is usually performed at about 16 weeks gestation, although it can be done safely at any time after 16 weeks gestation.

Amniocentesis is a relatively safe procedure in the hands of an experienced clinician. Clinician in this case is defined as the physician performing the amniocentesis. In most cases, the obvious benefits of knowing about your fetus prior to birth outweigh the risks of the procedure. Prior to having amniocentesis you should have counseling, which will provide you with understanding of the testing and the significance of any potential abnormal results.

Most women will feel a slight pressure or even a menstrual-like cramp when amniocentesis is performed. lt is rare to feel anything more than this.

Injury to the fetus during amniocentesis is rare. Continuous ultrasound monitoring is used during insertion of the amniocentesis needle. Care is taken to avoid placing the needle near the baby. Once the needle is in place we have no control over fetal movements. If per chance the baby were to come into contact with the needle, it would retreat away just as we would if we bumped into something sharp.

羊膜穿刺（Amniocentesis）

Indication:

Chromosome study

Fetal lung maturity

R/O chorioamnionitis (culture & gram stain)

Releasing polyhydramnios

Procedure:

ê 先以超音波找出最適宜下針處（羊水最多，並避開胎盤）。

ê 將Jelly擦掉，用Alc B-I及75% Alc消毒皮膚並鋪無菌罩單。

ê 將超音波探頭裝入消毒過之塑膠袋內。（不一定要用adaptor）

ê Sona guide下，以22#之羊水針抽出羊水。

（Chromosome study 20 ml; lung maturity & Gram stain/culture 10 ~ 15 ml）

附錄：

產前遺傳診斷適應症（衛生署）

1. 高齡產婦。

2. 本胎次有生育先天缺陷兒之可能者：?神經管缺陷?染色體異常（超音波或母血篩檢）?代謝異常?地中海型貧血。

3. 曾生育過先天缺陷兒者：?神經管缺陷?染色體異常?代謝異常?地中海型貧血或水胎。

4. 本人或配偶有遺傳疾病者：?性聯遺傳?染色體異常?代謝異常?地中海型貧血帶因

5. 家族中有遺傳疾病者：?性聯遺傳?染色體異常?代謝異常

6. 重複性流產。

7. 其他。

Risks of Amniocentesis

1.

Miscarriage. This happens spontaneously in 15-20% of all pregnancies, usually in early pregnancy before the time that amniocentesis would be performed. After amniocentesis, the risk of miscarriage is increased by less than 1% for the remainder of the pregnancy. Some miscarriages will happen anyway, but a few are caused by amniocentesis. Generally, the more experience the clinician has, the lower the miscarriage rate will be. In our experience, a pregnancy loss caused by an amniocentesis is probably less than one out of 500.

2.

Immediate risks. Cramping may occur during amniocentesis and for a short while afterwards. This is not significant. Bleeding and leaking of amniotic fluid occur only rarely and may mean a miscarriage is going to happen. You should contact your provider if any of this occurs.

3.

Infection. This is very rare. If this is going to happen, it usually occurs within 24 to 72 hours after the amniocentesis.

4.

Repeat testing needed. Very rarely, the clinician will not be able to obtain amniotic fluid, or the laboratory analysis will fail to yield results. This does not mean that something is wrong with you or your baby. If results are desired, then amniocentesis must be performed again.

Amniocentesis For Reasons Other than Genetic Testing

Amniocentesis can be performed during the second and third trimesters of pregnancy for a variety of reasons.

1.

During late gestation, analyzing the amniotic fluid can determine fetal lung maturity.

2.

When there is maternal blood sensitization (usually Rh sensitization), chemical tests can be performed on the amniotic fluid to verify fetal well-being.

3.

Testing the fluid for infection around the fetus can also be done at any time during the pregnancy.

What Tests are done on the Fluid?

If you are having the amniocentesis done for genetic reasons, there will be two tests performed on the fluid:

1.

Chromosome analysis. Fetal cells are extracted from the amniotic fluid and processed for chromosome studies. The most common chromosome abnormality is Down Syndrome. This test also determines the baby's sex.

2.

Alpha-fetoprotein (AFP). This test can help determine if there is an opening in the fetal skin. The most common place is the spine. This would be a neural tube defect, such as spina bifida or anencephaly.

Why Is it Important to Know your Blood Type and Rh Factor

If you are Rh negative you will need to receive a medication called Rhogam after the amniocentesis is performed. Whenever there is any chance that yours and the baby's blood can mix -- this is possible during amniocentesis -- it is recommended that you receive Rhogam. This medication can prevent complications with future pregnancies. If the baby's father is also Rh negative, you will not need to receive Rhogam. If you are Rh negative, ask your healthcare provider to supply you with information about what it means to be Rh negative.

1.	Miscarriage. This happens spontaneously in 15-20% of all pregnancies, usually in early pregnancy before the time that amniocentesis would be performed. After amniocentesis, the risk of miscarriage is increased by less than 1% for the remainder of the pregnancy. Some miscarriages will happen anyway, but a few are caused by amniocentesis. Generally, the more experience the clinician has, the lower the miscarriage rate will be. In our experience, a pregnancy loss caused by an amniocentesis is probably less than one out of 500.
2.	Immediate risks. Cramping may occur during amniocentesis and for a short while afterwards. This is not significant. Bleeding and leaking of amniotic fluid occur only rarely and may mean a miscarriage is going to happen. You should contact your provider if any of this occurs.
3.	Infection. This is very rare. If this is going to happen, it usually occurs within 24 to 72 hours after the amniocentesis.
4.	Repeat testing needed. Very rarely, the clinician will not be able to obtain amniotic fluid, or the laboratory analysis will fail to yield results. This does not mean that something is wrong with you or your baby. If results are desired, then amniocentesis must be performed again.

	Amniocentesis can be performed during the second and third trimesters of pregnancy for a variety of reasons.
1.	During late gestation, analyzing the amniotic fluid can determine fetal lung maturity.
2.	When there is maternal blood sensitization (usually Rh sensitization), chemical tests can be performed on the amniotic fluid to verify fetal well-being.
3.	Testing the fluid for infection around the fetus can also be done at any time during the pregnancy.