Why is amniocentesis done in Polyhydramnios?
The fetus (unborn baby) is present inside the uterus in the amniotic sac (the covering) that contains the amniotic fluid. The fluid provides nutrition to the developing baby and protects the baby from any external shocks or injuries. Amniocentesis is a medical procedure in which a small amount of amniotic fluid is removed and sent for lab examination to diagnose medical conditions. The procedure is usually done after the 15th week of pregnancy. Amniocentesis is also done for treatment purposes. The procedure in which amniocentesis is done to intentionally reduce the amniotic fluid volume is called amnioreduction. Amnioreduction helps in the treatment of polyhydramnios. This is a condition in which the amount of the amniotic fluid is more than what it should be for the gestational age. It is preferred particularly when the doctor has diagnosed the condition as severe polyhydramnios as in the case of twin-to-twin transfusion syndrome (TTTS). In TTTS, one twin gets an excess of blood, whereas the other has decreased blood flow. Besides removing the excess amniotic fluid, amniocentesis also helps diagnose the cause of polyhydramnios by laboratory examination of the amniotic fluid to look for any genetic conditions in the fetus.
Amnioreduction can be performed manually or with the help of vacuum-assisted devices (vacuum tubing and vacuum bottles). During the procedure, needles of different sizes (gauges) may be used (typically 18 or 20 gauge). The amount of the fluid removed depends on the severity of polyhydramnios. The procedure is generally done under sedation and numbing agents such as lidocaine may be used to reduce pain and discomfort. The patient lies on her back with a slight tilt toward her left side with the help of supporting pillows. The procedure is done under ultrasound guidance to ensure the safety of the mother and her baby. Medications may be given after the procedure to reduce any pain and complications.
What are the various indications for amniocentesis?
Amniocentesis may be done for various diagnostic and therapeutic reasons. It is helpful in the diagnosis of many genetic abnormalities in the fetus. Because the procedure carries some risks for the mother and the baby, amniocentesis is done when the doctor thinks that the benefits of the procedure outweigh the risks. The patient can refuse to go for the procedure, if she wants.
Amniocentesis may be done for
- The diagnosis of genetic diseases such as Down syndrome, cystic fibrosis and sickle cell disease.
- Testing fetal lung maturity, especially in cases where preterm labor (before 37 weeks of pregnancy) is planned or expected.
- The treatment of polyhydramnios, especially in cases of twin-to-twin transfusion syndrome (TTTS).
- The diagnosis of fetal infections.
- Determining paternity through DNA testing of the fetal cells present in the amniotic fluid.
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