thumb|Tubes filled with amniotic fluid for amniocentesis

Amniocentesis or amniotic fluid test (AFT) is a medical procedure used primarily in the prenatal diagnosis of genetic conditions.

Assessment of fetal lung maturity

Amniocentesis has traditionally been performed to assess the extent of fetal lung development in the context of medical and obstetrical complications, with the intention of delivering the fetus if fetal lung maturity is demonstrated. Lack of fetal lung maturity increases the risk of infant respiratory distress syndrome.

Fetal lung development can be tested by sampling the amount of surfactant in the amniotic fluid obtained via amniocentesis.

The efficacy of performing amniocentesis for the assessment of fetal lung maturity has been called into question. Based on this rationale, the risks associated with amniocentesis, and the limited indications, performing amniocenteses for assessing fetal lung maturity may become obsolete except in instances where gestational age is unknown. The gold standard for diagnosing chorioamnionitis is via a gram stain, glucose level, or culture of the amniotic fluid obtained via amniocentesis.

Amniocentesis can be used to detect other congenital infections such as cytomegalovirus, hepatitis B, parvovirus B19, and toxoplasmosis.

Assessment of severity of Rh isoimmunization

The Rh factor is an inherited protein found on the surface of red blood cells. If the mother is Rh negative and the father is Rh positive, a fetus has at least a 50% chance of being Rh positive. Rh sensitization typically does not cause problems during the first pregnancy of an Rh negative woman. Physicians have used the process of inserting a needle transabdominally into the uterus to extract excess amniotic fluid, also known as a reductive amniocentesis or decompression, for the management of polyhydramnios as early as the late 1800s. This process can result in polyhydramnios in one twin and oligohydramnios in the other twin. A potential benefit of using amniotic stem cells over those obtained from embryos is that they address the ethical concerns among anti-abortion activists by obtaining pluripotent lines of undifferentiated cells without harm to a fetus or destruction of an embryo. In addition, the use of embryonic cells has been shown to develop into tumors such as teratocarcinomas and frequently acquire chromosomal errors, underscoring the benefits of utilizing amniotic stem cells.

Research has shown that cells from second trimester amniotic fluid are successful at differentiating into various cell lines.

Artificial heart valves, working tracheas, as well as muscle, fat, bone, heart, neural and liver cells have all been engineered through use of amniotic stem cells. Tissues obtained from amniotic cell lines show significant promise for patients with congenital diseases/malformations of the heart, liver, lungs, kidneys, and cerebral tissue.

The first amniotic stem cells bank in the US is active in Boston, Massachusetts.

Contraindications

There are no absolute contraindications to amniocentesis. Relative contraindications to the procedure include failure to discontinue anticoagulation therapy 48–72 hours prior to amniocentesis, infections such as hepatitis B, hepatitis C, or human immunodeficiency virus (HIV), and oligohydramnios. There is an increased risk of mother-to-child (vertical) transmission of bloodborne infections in patients with hepatitis B, hepatitis C, or HIV after amniocentesis.

While not a contraindication, an amniocentesis may be postponed if fusion of the amnion and chorion has not yet occurred.

A serious risk of amniocentesis is pregnancy loss. The American College of Obstetricians and Gynecologists note that the pregnancy loss rates attributable to amniocentesis are very low. Studies from 2000 to 2006 estimated the procedure-related pregnancy loss at 0.6-0.86%. The most recent systematic review of the literature and updated meta-analysis on the risk of pregnancy loss following amniocentesis was published in 2019. This study cites the amniocentesis-related pregnancy loss to be 0.30% (95% CI, 0.11–0.49%).

The incidence of amniocentesis-related complications, including pregnancy loss and procedure failure, may be mitigated when performed by experienced practitioners who complete 100 or more amniocenteses per year. Experienced practitioners are more likely to complete the procedure with only one puncture attempt. Past literature has shown that twin pregnancies increase the background risk of fetal loss following amniocentesis before 24 weeks' gestation by 1%. The study also found no significant difference in rates of pregnancy loss between twin pregnancies that underwent amniocentesis and those that did not before 24 weeks of gestation.

  • Active vaginal infection
  • Maternal body-mass index greater than 40&nbsp;kg/m<sup>2</sup>
  • Multiparity, or 3 or more childbirths
  • History of 3 or more pregnancy losses
  • Carrying a fetus with structural malformations

Undergoing amniocentesis in the third trimester has been associated with an increased risk of preterm labor, as defined as the onset of labor between 20 and 37 weeks' gestation, and preterm delivery. When compared to cases of spontaneous PPROM, patients with amniocentesis-related PPROM experience better outcomes and lower rates of pregnancy loss. Therefore, possible consequences of oligohydramnios include infant respiratory distress and small, underdeveloped lungs known as fetal lung hypoplasia. In subsequent pregnancies with RhD positive fetuses, maternal presence of these antibodies can attack and destroy fetal red blood cells, a process called Rh isoimmunization that can result in a condition known as Rhesus disease or hemolytic disease of the fetus and newborn. Maternal blood type is assessed prior to undergoing amniocentesis and RhD immune globulin (RhoGam) is typically administered within 72 hours of the procedure to prevent maternal Rh sensitization in RhD negative patients that are non-sensitized to RhD antigens.

Amniotic fluid embolism, a condition in which amniotic fluid or other fetal debris enters the maternal circulation, is an extremely rare and catastrophic complication of amniocentesis. However, amniotic fluid embolism following amniocentesis has been reported infrequently in the literature in the last 60 years, mostly in the context of case-reports.

Chorioamnionitis and uterine and maternal skin infections are potential complications of amniocentesis that can occur as a result of bacterial introduction throughout the course of the procedure. The procedure-related risk of fetomaternal hemorrhage attributable to amniocentesis is 2.6%. 18-20 mL of amniotic fluid is slowly aspirated, with the first 1-2 mL typically discarded due to higher risk of maternal cell contamination. The types of tests performed on the sample will be determined by the patient's indications for undergoing amniocentesis. Fluorescent in-situ hybridization (FISH) and quantitative fluorescence polymerase chain reaction (QF-PCR) are two tests commonly performed on uncultured cells after amniocentesis, with results available within two days. Follow-up one week after the procedure is recommended to undergo ultrasound evaluation for fetal viability and assess healing of the puncture site. The provider may also administer a RhoGAM injection depending on the patient's and fetus' blood types to prevent reactions to differing Rh proteins.

Home care post-procedure

Common side effects

It is common for patients to experience mild cramping, abdominal pain, or pain at the insertion site. It is also common for patients to experience spotting or mild vaginal bleeding. Patients may feel fatigued and want to rest following the procedure.

Recommendations

Upon returning home from the procedure, it is recommended that the patient rests at home for 24 hours, avoiding strenuous activity such as exercising, running, heavy lifting, etcetera. It is also important to avoid sexual intercourse during this time. Practitioners often recommend acetaminophen, or Tylenol, to help alleviate any discomfort following the procedure. 650-1,000&nbsp;mg every 4 hours is standard. Do not exceed 4,000&nbsp;mg in 24 hours.

History

Physicians have used the process of inserting a needle transabdominally into the uterus to extract amniotic fluid for the management of hydramnios, or excess amniotic fluid, as early as the late 1800s. In 1930, needle insertion into the amniotic sac was used to inject contrast dye for the purposes of amniography, or radiographic visualization of the fetal, placental, and uterine outlines.

India and China have made prenatal sex determination illegal in an effort to prevent sex-selective abortion. In India, this happened through the 1994 Pre-Conception and Pre-Natal Diagnostic Techniques (Prohibition Of Sex Selection) Act (PCPNDT Act). However, this has not necessarily affected the widespread practice of sex-selective abortion as abortion is generally legal, and this law has been inconsistently enforced. In China, the societal preference for male children was exacerbated by the historical one-child policy, where in many regions of China, parents were limited to having only one child. As with India, prenatal sex determination is banned in China but remains a widespread practice, with enforcement also proving to be difficult.