Amniotic fluid contains about 500 mg/L of fat and about 40 mg/L of phospholipid. In the early stages of pregnancy, there were many sphingomyelins, and their contents did not change significantly during the entire pregnancy. Lecithin, which is an alveolar surfactant, is similar to sphingomyelin before 34 weeks of gestation and increases sharply after 34 weeks of gestation, making the lecithin/sphingomyelin ratio 2 or higher. This value can be regarded as fetal lung. Mature values, respiratory distress syndrome rarely occurs after the birth of a mature lung.

Basic Information

Specialist classification: maternity check check classification: biochemical examination

Applicable gender: whether women are fasting: not fasting

Analysis results:

Below normal:
L/S is less than 1.5 lungs are immature, and a considerable number of fetuses have respiratory distress syndrome. L / S 1.5 ~ 1.9 intermediate type, a small number of fetuses with respiratory distress syndrome.

Normal value:
Early pregnancy: 0-1
Full term pregnancy: 0-2

Above normal:
L/S>2 lung maturation, fetal respiratory distress syndrome does not occur.



Tips: The L/S ratio of some newborns is >2 in pregnant women with diabetes. Normal value

Early pregnancy <1:1.

Full-term pregnancy < 2:1.

Clinical significance

(1) L/S>2 lung maturation, the fetus does not have acute respiratory distress syndrome.

(2) L/S <1.5 lung immature, a considerable number of fetuses with acute respiratory distress syndrome.

(3) L/S 1.5~1.9 intermediate type, a small number of fetuses have acute respiratory distress syndrome.

In addition, the L/S ratio is affected by the following factors:

1 Lung maturity accelerates hypertension, kidney disease, diabetes, sickle cell anemia, premature separation of placenta (early placenta stripping), water breakage for more than 36 hours, intrauterine blood transfusion, use of glucocorticoids.

2 lung maturity retarded neonatal edema (fetal edema), diabetes.

Low results may be diseases: precautions for neonatal respiratory distress syndrome

In addition to premature babies susceptible to RDS, the L/S ratio of some newborns in pregnant women with diabetes is >2, and the incidence of RDS is higher than that of normal pregnant women. This should not be ignored.

Inspection process

There are three commonly used measurement methods, namely the standard curve method, the standard addition method and the internal standard method.

The internal standard method is to add the internal standard element (inside) to a series of standard samples (standard) and unknown samples, respectively, to measure the absorbance A, and to draw the standard of the concentration of the element to be tested C in the standard sample by the absorbance ratio of A/A. Curve, measured A sample / A internal absorbance ratio on the standard curve to determine the concentration of the element to be tested in the sample. The internal standard element should have similar characteristics to the measured element during the atomization process. The advantage of the internal standard method is that it can eliminate the error caused by the change of experimental conditions such as gas flow rate, atomization condition, flame state or graphite furnace temperature during the atomization process, and improve the precision of the measurement, but the application is limited by the performance of the instrument. That is, a two-channel atomic absorption spectrophotometer using two hollow cathode tubes as a light source is required for measurement.

Not suitable for the crowd

1, amniocentesis is generally carried out in the second trimester, early pregnancy, late stage should not be performed amniocentesis.

2, pregnant women have no cold and so on.

3, no amniotic fluid examination indications should not be carried out.

4. Check with the consent of the pregnant woman and her family members.

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) Injury of the fetus, placenta and umbilical cord: The puncture needle can damage the fetus and can cause bleeding, and the placenta and umbilical cord can also cause 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) Leakage of amniotic fluid: postoperative amniotic fluid leaks from the pinhole, causing too little amniotic fluid, affecting fetal development, and even causing miscarriage or premature birth.

(4) abortion or premature birth: the incidence of abortion or premature delivery is 0.1% -0.2%, often occurs within one week after surgery, even after the puncture, premature rupture of membranes leads to premature delivery.

(5) intrauterine infection: there may be maternal fever after surgery. Intrauterine infection can cause abnormal fetal development, or even fetal death. Therefore, amniocentesis should be strictly aseptic.