A transvaginal procedure performed during active labor where the fetal scalp is cleansed, pierced, and a small blood sample taken for evaluation.

You will be placed in the lithotomy position (on your back with knees and legs pulled towards your chest). If your cervix is already dilated at least 3 to 4 centimeters, then a plastic cone is placed in the vagina and snugged up against the scalp of the fetus. The scalp is cleansed and dried with long cotton swabs, and a small amount of petroleum jelly is applied to the scalp so fetal blood droplets will form beads and ease collection. A small puncture is made in the scalp and fetal blood droplets are collected in a thin glass tube. The tube is either sent to the hospital lab or analyzed by a machine on the labor floor. In either case, results are available in just a few minutes.

If you are unable to be still, it will be very difficult to perform this test. If your cervix is not dilated enough, then it is impossible to perform this test. The procedure typically takes about 5 minutes.

The procedure should feel like a long pelvic exam. At this stage of labor, many patients already have an epidural in place. They might not feel the procedure at all.

• Normal: 7.25 to 7.35
• Borderline 7.20 – 7.25
• Low: under 7.20

In general, low pH suggests that the baby is not tolerating labor very well. However, the results of a fetal scalp pH sample need to be interpreted in the context of each individual labor. Ask your doctor to explain your results to you after she gets the results. The doctor may think that the results are reassuring, and that labor may continue as before. Alternatively, she may feel that the results indicate that the baby needs to be delivered in a hurry, either by forceps or by cesarean section. Lastly, the results may not really point in either direction, and the test may need to be repeated in 20-30 minutes. Sometimes, it needs to be repeated a few times during a complicated labor.

Fetal scalp pH values do not correlate with your baby's Apgar scores. They do correlate with the pH of the umbilical cord artery, which is usually a little bit lower. Very low umbilical cord artery pH values can suggest that the fetus did not get enough oxygen in labor, but it can difficult to predict this based on the scalp pH value. Remember, scalp pH testing is only one of many tests by which your doctor can evaluate your baby during labor; the results must be interpreted in the context of your entire pregnancy. This is a complicated and very controversial subject in obstetrics, so please ask your doctor to explain any results to you.

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

This test may not be advised in mothers who are HIV+ or carry the hepatitis C virus. In these cases, your doctor may feel that the procedure increases the risk of transmitting infection to your baby.