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 lings are mature.

When is it used?

This test may be done if a baby needs to be delivered early. The test results help your healthcare provider predict whether the baby's lungs are developed enough for delivery.

How do I prepare for this test?

It can help to have a full bladder, so do not urinate before the test unless your healthcare provider tells you to do so. 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A small amount of fluid is withdrawn in a syringe and sent to the lab for testing.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 benefits of this test?

The test helps your healthcare provider see how mature the baby's lungs are. 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. If the baby needs to be delivered soon, the baby may be given a medicine 12 to 24 hours before delivery to try to help the lungs mature more quickly. The medicine is given as a shot to the mother.

What are the risks associated with this test?

The overall risk of complications from this procedure is very low. However, you should know what problems can occur. The following are possible problems or complications of amniocentesis:

• 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

When should I call my healthcare provider?

Call your healthcare provider right away if:

• You start having contractions or severe cramping. (It is normal to have some brief cramping for 4 to 6 hours after the test.)
• You have bloody or liquid vaginal discharge that does not stop. (It is normal to have a little spotting or leaking.)
• You develop a fever over 100°F (37.8°C).
• Your baby is moving less than before the test.

Call during office hours if:

• You have questions about the test or its result.
• You want to make another appointment.