Amniocentesis is the procedure for obtaining a small amount of amniotic fluid, which surrounds a developing baby during pregnancy to regulate temperature and provide protection from injuries. The clear, pale yellow-tinged fluid contains enzymes, proteins, hormones, and a variety of other substances including cells from the growing baby. The cells floating in the amniotic fluid contain genetic information. Collecting the fluid and cells with amniocentesis lets medical professionals diagnose chromosomal disorders and other potential health risks to the mother or baby.
A maternal serum -- or blood -- screening test is done before amniocentesis. Women using blood-thinning medications may need to stop taking them before the procedure and should follow any other doctors' instructions. A blood test determines blood type and Rh status (positive or negative). Amniocentesis to check for genetic abnormalities is usually done between the 15th and 20th week of pregnancy. If a woman is pregnant with twins or triplets, the doctor will perform amniocentesis for each baby inside of individual amniotic sacs. Identical twins share a single amniotic sac.
Many medical professionals recommend testing in the second trimester of pregnancy if the mother has a family history or previous child with a genetic disorder such as Down syndrome, Tay Sachs disease, or cystic fibrosis. Other reasons for second-trimester testing include the risk of open neural tube defects such as spina bifida, a risk of a sex-linked genetic disorder, abnormal screening tests, or a maternal age of 35 or older.
Using an ultrasound, the doctor will check the location of the uterus and the baby's position. She will apply a special gel for the ultrasound transducer. After the image from the ultrasound is clear on the monitor, she will apply a numbing medication. A hollow needle is inserted into the belly to withdraw a tiny amount of amniotic fluid -- usually just a few teaspoons. The mother may feel a slight stinging or cramping. General precautions include bed rest after the procedure and avoiding strenuous activity for a few days.
Signs and symptoms of which to be aware after amniocentesis include fever, vaginal bleeding or fluid leakage, change or sudden decline of fetal movement, and inflammation at the insertion site. Women should contact a doctor if they experience any of these signs. An amniotic embolism is a very rare complication of amniocentesis but is a medical emergency. Signs include unexplained bleeding, difficulty breathing, and sudden pain in the back or chest.
Cells from the amniotic fluid are grown and analyzed in a lab. The results of genetic analysis are usually available between ten days and two weeks after the procedure. The results from lung maturity tests are ready within hours. Amniocentesis in the third trimester may be done to diagnose a uterine infection. Results of a sample to identify infection can be ready within hours or days, depending on the cause. Amniocentesis can also remove excess amniotic fluid in rare cases where the fetus and mother's body produce too much fluid.
Fetal lung maturity amniocentesis can evaluate the baby's lungs when there is a risk of early delivery. Early delivery can occur through induction, a C-section, or premature labor. Doctors may insist on medically initiated premature birth if complications during pregnancy put the mother or baby at risk. Likewise, many factors may prompt a doctor to halt unintentional premature labor, including fetal lung maturity. If the doctor cannot stop unintentional premature labor, the information from the amniocentesis guides emergency measures for the premature baby.
The risk of miscarriage is highest if the doctor does amniocentesis during the first 15 weeks of pregnancy. There is only a very slight risk of miscarriage during the second trimester. Needle injuries are possible if the baby moves an arm or leg during the procedure, but such injuries are rare. Amniocentesis also carries a slight risk of uterine infection.
There is always some risk involved with amniocentesis, but some health issues make the procedure too risky to carry out. Amniocentesis may not be advisable if the mother has HIV or AIDS, hepatitis B, or hepatitis C because these viruses can be passed on to the baby during the procedure. Some sexually transmitted diseases may pose a risk as well. Medical care providers assess each case individually.
In rare cases, amniocentesis allows the baby's blood cells to enter the mother's bloodstream. This is only a serious problem if a mother has Rh-negative blood and the baby has Rh-positive blood; in these instances, medical staff will give the mother an injection of Rh immune globulin to stop the mother's body from producing Rh antibodies that could cross the placenta and harm the baby's red blood cells.
Most of the time, amniocentesis results are normal. A normal result is not a guarantee that the baby will be completely healthy. Amniocentesis can only help identify known and identified genetic abnormalities, so it cannot find every possible condition. Amniocentesis results overall have 98 to 99% accuracy. Parents often consult with geneticists, specialists, and pediatricians before making any decisions.
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