Amniotic fluid sodium test can predict fetal maturity. As the hypoemic urine of the fetus enters the amniotic fluid, the amniotic fluid gradually becomes hypotonic, and the sodium and chlorine are slightly decreased, and the potassium is slightly increased. There were no changes in calcium, magnesium, phosphorus, zinc, iron, sulfur and manganese. Sodium emits light of a certain wavelength under flame excitation. The wavelengths of sodium emission are 765 nm and 589 nm, respectively, and the light intensity is proportional to its concentration within a certain range.

Basic Information

Specialist classification: maternity check check classification: biochemical examination

Applicable gender: whether women are fasting: not fasting

Tips: Generally, about 20ml of amniotic fluid is taken and placed in a clean and sterilized centrifuge tube. Normal value

Early pregnancy is equivalent to about 136 ~ 146mmol / L of serum sodium.
Full-term pregnancy is 7-10 mmol/L lower than blood sodium (7-10 mEq/L lower than blood sodium).

Clinical significance

Increased in Cushing's syndrome, primary aldosteronism, ACTH tumor, brain trauma, cerebrovascular accident, heart failure, renal failure, cirrhosis, severe water loss, excessive sodium intake and renal insufficiency .

High results may be diseases: attention to macrosomia and renal insufficiency

1, the amniotic fluid should be separated in time to avoid hemolysis. Otherwise, the K+ content may be significantly increased due to the escape of K+ in the cells.

2. Place the measuring tube and standard tube in the same position and liquid level, otherwise the result may be affected.

3. The air pressure and the pressure of the combustible gas should be constant during the measurement process.

4, patient preparation: before the test, the test should stop diuretics and cortisol hormone drugs. Various diuretics can reduce Na+ and K+, and adrenaline, guanethidine, corticosteroids, etc. can increase Na+ and decrease K+.

5, sample dilution: the best sample is to use a micro-sampler, distilled water must meet the requirements, the utensils used must be clean.

6. Quality control specimens are taken daily with daily specimens.

7. When the standard solution is prepared, its concentration must be strictly checked.

Inspection process

Amniocentesis is usually performed in the second trimester (16-21 weeks of gestation). The urine should be drained before surgery, with both hands on the hips and 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: The amniotic fluid and the standard solution were diluted 100 times with distilled water. Zero the distilled water and measure the light intensity of the standard solution and amniotic fluid.

Not suitable for the crowd

1. It is not advisable for pregnant women to have a cold.

2. The consent of pregnant women and their families should be obtained before surgery. Those without indications should not be carried out.

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.