Fetal blood testing – scalp; Fetal distress – fetal scalp testing; Labor – fetal scalp testing
Fetal scalp pH testing is a procedure performed when a woman is in active labor to determine if the baby is getting enough oxygen. Fetal scalp blood testing is a technique used in obstetrics during labor to confirm whether fetal oxygenation is sufficient. The procedure can be performed by creating a shallow cut by a transvaginally inserted blood lancet, followed by applying a thin pipe to the site that samples blood by capillary action.
How the Test is Performed
The procedure takes about 5 minutes. The mother lies on her back with her feet in stirrups. If her cervix is dilated at least 3 to 4 centimeters, a plastic cone is placed in the vagina and fit snugly against the scalp of the fetus.
The scalp of the fetus is cleansed and a small blood sample is taken for examination. The blood is collected in a thin tube. The tube is either sent to the hospital laboratory or analyzed by a machine in the labor and delivery department. In either case, results are available in just a few minutes.
If the woman’s cervix is not dilated enough, the test cannot be done.
How to Prepare for the Test
The health care provider will explain the procedure and its risks. There isn’t always a separate consent form for this procedure because many hospitals consider it part of the general consent form you signed at admission.
How the Test will Feel
The procedure should feel like a long pelvic exam. At this stage of labor, many women have already had epidural anesthesia and may not feel the pressure of the procedure at all.
Why the Test is Performed
Sometimes fetal heart monitoring doesn’t provide enough information about the well-being of a baby. In these cases, testing the scalp pH can help the doctor decide whether the fetus is getting enough oxygen during labor. This helps determine whether the baby is healthy enough to continue labor, or if a forceps delivery or cesarean birth might be the best route of delivery.
Although the test is not uncommon, most deliveries do not involve fetal scalp pH testing.
This test is not recommended for mothers with infections such as HIV/AIDS or hepatitis C.
Normal Results
Normal fetal blood sample results are:
- Normal pH: 7.25 to 7.35
- Borderline pH: 7.20 to 7.25
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
A fetal scalp blood pH level of less than 7.20 is considered abnormal.
In general, low pH suggests that the baby does not have enough oxygen. This may mean that the baby is not tolerating labor very well. The results of a fetal scalp pH sample need to be interpreted for each labor. The provider may feel that the results mean the baby needs to be delivered quickly, either by forceps or by C-section.
Fetal scalp pH testing may need to be repeated a few times during a complicated labor to keep checking on the baby.
Risks
Risks include the following:
- Continued bleeding from the puncture site (more likely if the fetus has a pH imbalance)
- Infection
- Bruising of the baby’s scalp
FAQ
How is fetal scalp sampling done?
- The scalp of the fetus is cleansed and a small blood sample is taken for examination. The blood is collected in a thin tube. The tube is either sent to the hospital laboratory or analyzed by a machine in the labor and delivery department. In either case, results are available in just a few minutes.
What does fetal scalp stimulation do?
- The fetal scalp stimulation test is a diagnostic test used to detect fetal metabolic acidemia. It can be used as a non-invasive alternative to fetal scalp blood testing.
When is a fetal scalp electrode used?
- Fetal scalp electrode plays a key role in intrapartum fetal surveillance when there is a non-reassuring fetal heart rate (FHR) tracing or when external FHR monitoring is difficult due to maternal body habitus or excessive fetal movement. It is estimated that FSE is used in 20% of the U.S. obstetrical population.
Does fetal scalp stimulation diagnose fetal hypoxia?
- The effectiveness of the scalp stimulation test was poor for both ruling in and out fetal hypoxia during labor. The absence of a provoked acceleration seems to be a normal phenomenon in the second stage of labor.
Which of the following is a disadvantage of fetal blood sampling?
- The risks of fetal blood sampling include: Bleeding from the fetal blood sampling site. Changes in the baby’s heart rate. Infection.
What is a fetal scalp electrode?
- A scalp electrode is applied to a fetus’ scalp which monitors the baby’s heart, similar to an ECG. A scalp electrode monitors a fetus’ heart rate more accurately than an external monitoring method for a variety of reasons.
Under what clinical situation should conducting fetal scalp stimulation be considered?
- Digital fetal scalp stimulation is recommended as an indirect assessment of acid-base status in response to atypical or abnormal electronic fetal monitoring tracings (II-B). Fetal scalp blood sampling should be considered when available (II-B).
When is a fetal scalp electrode contraindication?
Contraindications:
- The electrode should NOT be applied to a malpresentation, when placenta previa or excessive vaginal bleeding is present, when genital infections (e.g., herpes, Group B strep, gonorrhea) or blood-borne diseases (e.g., Hepatitis B carrier, HIV carrier) exist, or when it is not possible to identify.
Does a fetal scalp electrode hurt the baby?
- During internal fetal monitoring, your doctor tries to place the transducer on the baby’s scalp as gently as possible. In some cases, the transducer might cause some injury to your baby. Examples of potential injuries include bruising and scratching. These markings typically heal quickly without any complications.
Can fetal scalp electrodes detect maternal heart rate?
- They are less common with the application of a fetal scalp electrode which will often give the true fetal heart rate signal (see Fig. 3), but may, in some circumstances still occur, particularly after fetal death with a recording of the maternal heart rate.
How is fetal blood type tested?
- This can be measured using an ultrasound scan called a Doppler ultrasound. If a Doppler ultrasound shows your baby’s blood is flowing faster than normal, a procedure called fetal blood sampling (FBS) can be used to check whether your baby is anemic (iron deficiency anemia).
How do you remove fetal scalp electrodes?
- To remove the electrode: a. Detach the FSE from the leg plate adapter cable b. Grasp the electric wires as close as possible to the fetal presenting part and rotate the electrode counterclockwise until it is free from the fetal presenting part. Do not pull the electrode from the fetal skin.
What are the advantages of a scalp electrode in monitoring fetal heart rate?
- This type of electrode is sometimes called a spiral or scalp electrode. Internal monitoring provides a more accurate and consistent transmission of the fetal heart rate than external monitoring because factors such as movement do not affect it.
How would you distinguish between fetal and maternal heart rates?
- Early in labor, the normal fetal heart rate (110–160 BPM) typically exceeds the basal maternal heart rate. However, in the presence of chorioamnionitis and maternal fever or with the stress of maternal pushing, the maternal heart rate frequently approaches or exceeds that of the fetal heart rate.
