Fetal blood testing

How the Test is Performed:
This test may not be advised if you have had a premature rupture of membranes (your water broke prematurely), or if you have an active cervical infection. If one or both of these conditions exist, the fetus could be unduly exposed to infection by the procedure.

You will be placed in the lithotomy position (on your back with knees and legs pulled towards your chest). Your cervix is dilated and an amnioscope (endoscope) is inserted to directly view the fetus, through your vagina . The fetus' scalp is cleansed and dried, then a small amount of petroleum jelly is applied to the scalp so fetal blood droplets will bead and ease collection. A small puncture is made in the scalp and fetal blood droplets are collected in a thin glass tube.

This procedure typically takes between 10 and 15 minutes.

How to Prepare:
Your health care provider explains the procedure and its risks. You will be asked to wear a hospital gown, and to sign a consent form before the procedure.

How it Feels:
Many patients report feeling mild vaginal pain and cramping similar to that experienced during menses after the procedure.

Risks:
Risks include:
  • continued bleeding from the puncture site (more likely if the fetus has a pH imbalance)
  • infection
  • fetal scalp bruising



Why this Test is Performed:
Usually this test is performed to obtain information about fetal acid-base balance (blood pH). This is a strong indicator of fetal distress, and low blood pH directly correlates with low APGAR scores (a test that measures how well your baby is doing directly after birth). Therefore, it is the goal of your health care provider to avoid fetal distress, and this test provides direct and measurable results.

The test may also be used to measure fetal blood gases .

For most deliveries and pregnancies, this test is not necessary.

Normal Values:

  • pH: 7.25 to 7.35
  • O2 saturation: 30% to 50%
  • PO2: 18 to 22 mm Hg
  • PCO2: 40 to 50 mm Hg

Note: mm Hg = millimeters of Mercury

Abnormal Results:
A low pH and decreased oxygen saturation indicates fetal distress and need for immediate delivery.