Amniocentesis foam test can reflect fetal lung maturity. The monitoring of fetal maturity is an important basis for determining the reasonable delivery time and treatment policy for high-risk pregnancy. It is mainly to observe whether the fetal organ function is perfect through the growth and decline of a certain substance in the amniotic fluid. Amniotic fluid specimens are usually obtained by amniocentesis by a general practitioner.

Basic Information

Specialist classification: maternity check check classification: biochemical examination

Applicable gender: whether women are fasting: not fasting

Analysis results:

Below normal:

Normal value:

Above normal:

Negative fetal lungs are not yet mature.

Positive fetal lungs are mature.

Tips: Amniocentesis is usually performed in the second trimester (16-21 weeks of gestation). Normal value

Both the first and second tubes were positive.

Clinical significance

Positive fetal lungs are mature.

Negative fetal lungs are not yet mature.

This test can be used to determine neonatal idiopathic respiratory distress syndrome and reduce neonatal mortality, especially in patients with pregnancy-induced hypertension and hypertension combined with pregnancy can reduce neonatal mortality.

Positive results may be diseases: neonatal respiratory distress syndrome, congenital lung hypoplasia

1, amniocentesis is generally performed in the second trimester (pregnancy 16-21 weeks).

2. When the first tube is negative, it indicates that the fetal lung is immature, and the first tube is positive. The second tube is negative, indicating that the fetal lung is mature, and the first and second tubes are positive, indicating that the lung is mature.

Inspection process

Collect amniotic fluid specimens: empty urine before surgery, akimbo with both hands, gently turn the waist and abdomen. Then supine, use B-ultrasound to detect the positioning, select the puncture point, and puncture under strict aseptic operation conditions. Generally, about 20 ml of amniotic fluid is taken and placed in a clean and sterilized centrifuge tube for immediate inspection.

Detection method: foam test method.

This test is the most commonly used bedside test, generally taking 2 test tubes. The ratio of the first tube of amniotic fluid to 95% ethanol is 1:1, and the ratio of the second tube is 1:2. After vigorously shaking for 15-20 seconds, after standing for 15 minutes, if there is still a complete foam ring on the surface of the second tube, the L/S ratio is greater than or equal to 2, suggesting that the fetus is mature, such as only the entire tube surface has a complete foam ring. , L / S ratio may be <2; if the two tubes do not see the foam ring, it indicates that the fetus is immature. A further accurate amniotic fluid foam test can also perform a series of dilution tests with amniotic fluid and 95% ethanol.

Some substances in amniotic fluid can reduce the surface tension of water, and after shaking, a stable foam can be formed at the gas-liquid interface. In the presence of anti-foaming agent ethanol, foams formed by proteins, bile salts, free fatty acids and unsaturated phospholipids are rapidly destroyed in a few seconds. The alveolar surfactant saturated phospholipid in amniotic fluid is a hydrophilic and lipophilic amphoteric interfacial substance. The foam formed by it can be kept at room temperature for several hours, so it can be stabilized around the edge of the test tube at the gas-liquid interface after shaking. Foam layer.

Not suitable for the crowd

Amniocentesis is an invasive examination, puncture should be carefully decided, and full understanding and consent of pregnant women and their families are required before surgery.

1, generally in the second trimester (pregnancy 16-21 weeks). Early pregnancy, late stage should not be checked.

2, no puncture appropriate symptoms should not be carried out.

If there are no other special reasons, one of the following indications must be available:

1. When there is indication for induction of labor in high-risk pregnancies, the maturity of the fetus can be understood, combined with the measurement of placental function, and the time of induction of labor is determined to reduce the perinatal mortality.

2. There have been many unexplained abortions, premature birth or stillbirth history, suspected of having a hereditary disease in the fetus; those who have been married to chromosomal abnormalities; one or both of the couples have chromosomal abnormalities or parents with metabolic defects.

3.35-40 years old pregnant women, talking about fetal chromosomal abnormalities.

4. Necessary fetal gender diagnosis.

5. Have had a serious viral infection in early pregnancy or have been exposed to large doses of ionizing radiation.

6. The maternal fetal blood type is inconsistent and judge the prognosis of the fetus.

7. If there is a suspected premature rupture of membranes, the PH and smear of the vaginal fluid can be used to check whether the amniotic fluid forms crystals and fat cells to determine whether it is amniotic fluid.

Adverse reactions and risks


1, maternal injury: puncture needle stab wound blood vessels caused by abdominal wall hematoma uterine subserosal hematoma. Occasionally, amniotic fluid enters the maternal blood circulation from the puncture hole and causes amniotic fluid embolism. The bladder was not emptied before the puncture, and the bladder was injured.

2, damage to the fetus, placenta and umbilical cord: puncture needle damage to the fetus can occur bleeding, stab wounds and umbilical cord can also occur bleeding or hematoma. Therefore, the source of bleeding should be identified when taking hemorrhagic amniotic fluid. If you suspect that you are from a fetus, you should continue to listen to the fetal heart.

3, amniotic fluid leakage: postoperative amniotic fluid leakage from the needle hole, resulting in too little amniotic fluid, affecting fetal development, and even cause miscarriage or premature birth.

4, abortion or premature delivery: the incidence of abortion or premature birth 0.1% -0.2%, often occurred within one week after surgery, even after the puncture, premature rupture of membranes leading to premature delivery.

5, intrauterine infection: postpartum may have maternal fever. Intrauterine infection can cause abnormal fetal development, or even fetal death. Therefore, amniocentesis should be strictly aseptic.