Serial Amniocentesis

TTTS. Serial Amniocentesis

Amniocentesis is the standard screening technique for fetal anemia, because amniotic fluid contains hemolytic products excreted from the fetal kidneys and lungs, including bilirubin.

Amniocentesis (also referred to as amniotic fluid test or AFT) is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, and also for sex determination, in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amniotic sac surrounding a developing fetus, and then the fetal DNA is examined for genetic abnormalities. 

The most common reason to have an "amnio" is to determine whether a baby has certain genetic disorders or a chromosomal abnormality, such as Down syndrome. Amniocentesis (or another procedure, called chorionic villus sampling (CVS)) can diagnose these problems in the womb. Amniocentesis is performed when a woman is between 14 and 16 weeks gestation. 

Women who choose to have this test are primarily those at increased risk for genetic and chromosomal problems, in part because the test is invasive and carries a small risk of miscarriage. This process can be used for prenatal sex discernment and hence this procedure has legal restrictions in some countries. Amniocentesis was first introduced by American obstetrician Fritz Friedrich Fuchs and Danish gastroenterologist Polv Riis in 1956 for fetal sex determination and up to mid 1970s amniocentesis were done 'blind‘. 

Doctors Jens Bang and Allen Northeved from Denmark were the first to report amniocentesis done with the guide of an ultrasound in 1972. Chorionic Villus Sampling (CVS) was first performed by Italian biologist Giuseppe Simoni in 1983. Now real-time ultrasound is used during all invasive procedures because it provides for the safety of the fetus and accuracy of results.

What is amniocentesis?

Amniocentesis is a procedure used to obtain a small sample of the amniotic fluid that surrounds the fetus during pregnancy. Amniotic fluid is a clear, pale yellow fluid made by the fetus. The fluid protects the fetus from injury and helps to regulate the temperature of the fetus.

In addition to various enzymes, proteins, hormones, and other substances, the amniotic fluid contains cells shed by the fetus. These cells contain genetic information that can be used to diagnose chromosomal disorders and open neural tube defects (ONTDs), such as spina bifida. Testing may be available for other genetic defects and metabolic disorders depending on the family history and availability of lab testing at the time of the procedure.

Amniotic fluid also contains other substances that provide information about certain conditions. An amniocentesis may be performed in late pregnancy to check fetal well-being and diagnose fetal conditions, such as infection. An amniocentesis may be performed to check for fetal lung maturity if a baby is expected to be delivered early. Specific substances present in the amniotic fluid can be measured or tested for these conditions.

The fluid is sent to a genetics lab so that the cells can grow and be analyzed. Results are usually available in about 10 days to two weeks, depending on the lab. Results from fetal lung maturity tests are available within a few hours.

An amniocentesis is generally offered to women between the 15th and 20th weeks of pregnancy who are at increased risk for chromosome abnormalities. This includes women who are over 35 years of age at delivery, or those who have had an abnormal maternal serum (blood) screening test indicating an increased risk for a chromosomal abnormality or neural tube defect.

Amniocentesis helps confirm a tentative diagnosis of an abnormality previously found with other testing. It may also find that a fetus does not have the abnormality that was suspected.

Another related procedure that may be used to diagnose genetic and chromosomal defects is chorionic villus sampling (CVS). Please see this procedure for additional information.

Amniocentesis in Twin-Twin Transfusion Syndrome

Prior to 2001, several small-number case series had been published regarding the use of serial amnioreduction as originally suggested by Saunders et al.1 The rationale for the use of amniocentesis was to decrease the likelihood of miscarriage and preterm labor associated with polyhydramnios in the sac of the recipient twin. In addition, improved placental perfusion to the donor twin was also thought to result from this intervention.

A wide-range of survival rates from 33 to 83% had been reported. In an effort to compile the available experience at the time, Mari et al set up an international registry of TTTS patients treated with serial amnioreduction. 15 A total of 223 patients, from 20 centers, treated before 28 weeks’ gestation were analyzed. It is unclear from the study if the cases included patients that were previously published, unpublished, or both. 

The definition of TTTS was left to the discretion of the each investigator. As a result at least 17% of patients did not have a stuck twin. Complications from the procedure within 48 hours included ruptured membranes 6%, spontaneous delivery 3%, fetal distress 2.2%, fetal death 1.7%, and placental abruption 1.3%, with an overall risk of complications of 15%. The median interval from amniocentesis to delivery was 17.5 days. At least one fetus survived in 70.8% of patients, and both twins survived in 48% of cases. 

The incidence of postnatal abnormal intracranial imaging was 18%. Logistic regression showed that poor prognostic factors included early gestational age (<22 weeks), more than 1 liter of fluid removed per week, absent end-diastolic velocity in the umbilical artery of the donor twin, and hydrops.15 Although this study was the largest series at the time, it was a retrospective analysis without a clear sonographic definition of the syndrome that included patients up to 28 weeks of gestation. In addition, the relatively few number of patients, considering the large number of centers involved, also point to a limited experience by most centers or the potential for bias by a single center that would concentrate management. 

The actual number of patients per center was not provided. Nonetheless, the results confirmed that serial amniocentesis was superior than historical controls managed expectantly. However, the relatively short time, in terms of pregnancy prolongation, gained after the procedure and the high incidence of neonatal neurological morbidity were apparent. The study pointed out risk factors associated with poor perinatal outcome, and constituted the basis for the design of a randomized clinical trial comparing serial amniocentesis with laser therapy. 

Table 11-3 shows the experience with serial amniocentesis as reported in the literature for 1990–2005. The table does not include the amniocentesis registry to avoid overlap, because, as mentioned above, many prior reports could have been included in the registry. Also, the table does not include series comparing amniocentesis with laser. Of the 24 studies available, only 5 used a standard sonographic definition of TTTS similar to the polyhydramnios MVP ?8 cm, oligohydramnios MVP ?2 cm criteria used today,16–20 and only 3 studies used a gestational age of 26 weeks as the upper limit for inclusion.

Only 13 studies reported on neurological morbidity. The overall survival rate for at least one fetus was 68% (243/355), with an associated neurological morbidity of 22.9% (103/449). Despite the lack of use of a standard definition of TTTS and the potential for bias for inclusion of non-TTTS patients, the overall perinatal survival rate of TTTS in these studies is somewhat similar to that reported in studies using standardized criteria (see below). A common finding in these studies is the high rate of neurological morbidity. Level of evidence: II-3.

Amniocentesis Risks

Amniocentesis carries various risks, including:

• Leaking amniotic fluid. Rarely, amniotic fluid leaks through the vagina after amniocentesis. However, in most cases the amount of fluid lost is small and stops within one week, and the pregnancy is likely to proceed normally. 
• Miscarriage. Second-trimester amniocentesis carries a slight risk of miscarriage — about .6 percent. Research suggests that the risk of pregnancy loss is higher for amniocentesis done before 15 weeks of pregnancy. 
• Needle injury. During amniocentesis the baby might move an arm or leg into the path of the needle. Serious needle injuries are rare. 
• Rh sensitization. Rarely, amniocentesis might cause the baby's blood cells to enter the mother's bloodstream. If you have Rh negative blood and you haven't developed antibodies to Rh positive blood, you'll be given an injection of a blood product called Rh immune globulin after amniocentesis. This will prevent your body from producing Rh antibodies that can cross the placenta and damage the baby's red blood cells. A blood test can detect if you've begun to produce antibodies. 
• Infection. Very rarely, amniocentesis might trigger a uterine infection. 
• Infection transmission. If you have an infection — such as hepatitis C, toxoplasmosis or HIV/AIDS — the infection might be transferred to your baby during amniocentesis. 

Remember, genetic amniocentesis is typically offered when the test results might have a significant impact on management of the pregnancy. Ultimately, the decision to have genetic amniocentesis is up to you. Your health care provider or genetic counselor can help you weigh all the factors in the decision.

Amniocentesis: Before the procedure

• The doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
• You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.
• Generally, there is no special restriction on diet or activity prior to an amniocentesis.
• Notify your doctor if you are sensitive to or are allergic to any medications, latex, tape, and anesthetic agents (local and general).
• Notify your doctor of all medications (prescription and over-the-counter) and herbal supplements that you are taking.
• Notify your doctor if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.
• Notify your doctor if you are Rh negative. During the amniocentesis, blood cells from the mother and fetus can mix. This may lead to Rh sensitization and breaking down of fetal red blood cells.
• You may or may not be asked to empty your bladder right before the procedure. In early pregnancy, a full bladder helps move the uterus into a better position for the procedure. In later pregnancy, your bladder should be empty to minimize the risk of puncture with the amniocentesis needle.
• Based upon your medical condition, your doctor may request other specific preparation.

Amniocentesis: During the procedure

An amniocentesis may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor’s practices.

Generally, an amniocentesis follows this process:

1. You will be asked to undress completely, or from the waist down, and put on a hospital gown.
2. You will be asked to lie down on an exam table and place your hands behind your head.
3. Your vital signs (blood pressure, heart rate, and breathing rate) will be checked.
4. An ultrasound will be performed to check the fetal heart rate, the position of the placenta, fetus, and umbilical cord, and to locate a pocket of amniotic fluid.
5. Your abdomen will be cleansed with an antiseptic. You will be instructed not to touch the sterile area on your abdomen during the procedure.
6. You will feel a needle stick if a local anesthetic is injected. This may cause a brief stinging sensation.
7. Ultrasound will be used to help guide a long, thin, hollow needle through your abdomen, into the uterus and the amniotic sac. This may be slightly painful. You may feel some cramping as the needle enters the uterus.
8. The doctor will withdraw a small amount of amniotic fluid into a syringe. The amount depends upon the type of testing that will be performed, but usually no more than an ounce is removed. You may feel a tugging or pulling sensation as the fluid is removed.
9. The fluid will be placed into a special light-protected container.
10. The needle will be removed.
11. An adhesive bandage will be placed over the needle site.
12. The fetus’ heart rate and your vital signs will be reassessed.
13. If you are Rh negative, you may be given Rhogam, a specially developed blood product that can prevent an Rh negative mother's antibodies from reacting to Rh positive fetal cells.
14. The amniotic fluid will be sent to the lab for examination.

Amniocentesis: After the procedure

You and your fetus will be monitored for a time after the procedure. Your vital signs and the fetal heart rate will be checked periodically for an hour or longer.

Amniotic fluid for genetic and chromosome testing will be sent to a specialty genetics lab for analysis. Alpha-fetoprotein, a protein made by the fetus that is present in the fluid, may also measured to rule out an open neural tube defect, such as spina bifida. Testing may also be done for other substances related to metabolic or genetic conditions. Depending on test results, counseling with a genetics specialist may be recommended.

You may feel some cramping during or after the amniocentesis. If you feel lightheaded, dizzy, or nauseated, notify the nurse. You may be instructed to rest on your left side.

You should rest at home and avoid strenuous activities for at least 24 hours, or as directed by your doctor.

Notify your physician to report any of the following:

• Any bleeding or leaking of amniotic fluid from the needle puncture site or the vagina
• Fever and/or chills
• Severe abdominal pain and/or cramping
• Changes in the activity level of your fetus (if you are past 20-24 weeks of pregnancy)

Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.