Fetal Lung Maturity Test

What is a fetal lung maturity test?

A fetal lung maturity test checks an unborn baby's lungs to see how fully developed the lungs are. The test can help your healthcare provider know if the baby might have breathing problems after birth, such as a problem called respiratory distress syndrome.

For the test, your healthcare provider does a procedure called amniocentesis to take fluid from inside the amniotic sac. The amniotic sac, also called the bag of waters, is a thin sac filled with fluid. It surrounds the baby in the uterus (womb). The sample of amniotic fluid is tested in the lab to see if the baby’s lungs are mature.

When is it used?

This test may be done if a baby may need to be delivered early. The test results help your healthcare provider know if the baby's lungs are developed enough for delivery. If the lungs are not fully developed, the baby could have serious problems breathing after birth. In this case, your provider may decide not to deliver the baby until the lungs are more mature, or the mother may be given a medicine to help the baby’s lungs mature more quickly.

How do I prepare for this test?

It can help to have a full bladder, so don’t urinate before the test unless your healthcare provider tells you to. Follow any other instructions your healthcare provider gives you.

What happens during the test?

The baby's heart rate is checked before and after the test.

Your abdomen is cleaned with a liquid antiseptic solution. It is usually not necessary to use numbing medicine before performing this test.

Your healthcare provider uses ultrasound images to help guide a thin needle through your abdomen, into the uterus, away from the baby, and to the area where the most amniotic fluid is. Like when you have your blood drawn, you may feel some brief and mild discomfort when the needle is inserted into the skin of your abdomen.

A small amount of fluid is withdrawn in a syringe and sent to the lab for testing.

What happens after the test?

Depending on the reason for the test, you may go home after the test or you may stay in the hospital. You should rest for 24 hours after the test.

The results of the test should be available in 6 hours to 1 day.

What are the risks of this test?

Your healthcare provider will explain the procedure for the test and any risks. The risk of complications from this test is very low. Some possible risks include:

  • Bleeding
  • Infection
  • Harm to the baby, placenta, or umbilical cord by the needle
  • Premature breaking (rupture) of the amniotic sac
  • Premature contractions or labor
  • Injury to a nearby organ
  • Not being able to get amniotic fluid for the test

Ask your healthcare provider how these risks apply to you. Be sure to discuss any other questions or concerns that you may have.

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