Internal fetal monitoring: scalp electrode and pressure catheter prerequisites and risks

When internal monitoring is chosen

External monitoring is usually adequate and similarly reliable. Internal devices are considered when the external tracing is poor, for example with maternal obesity or movement, or when the team needs precise information about contraction strength, such as in suspected labour dystocia. Choosing internal monitoring is a provider decision made after weighing benefits against risks. Explaining the reason for the change helps the patient understand why an internal device is being suggested.

A fetal scalp electrode is a small spiral attached to the presenting part to produce a continuous fetal heart signal. An intrauterine pressure catheter is passed beside the fetus into the uterine cavity to measure the pressure of contractions and resting tone, and it can also be used for amnioinfusion.

Prerequisites the nurse confirms

Both devices require ruptured membranes and enough cervical dilation to pass the device. The presenting part must be identified before a scalp electrode is applied. Placental location should be known before catheter insertion, and the catheter is placed away from the placental site using sterile technique. If membranes are intact, the provider must decide whether artificial rupture is appropriate, which is a separate decision with its own risks, including cord prolapse.

Check the maternal infection history. Fetal scalp electrodes create a potential entry point for viruses, and they are a recognised risk factor for neonatal herpes simplex infection. Many protocols also avoid scalp electrodes when the mother has HIV or hepatitis B or C, or when a fetal bleeding disorder is known or suspected, because the electrode breaches fetal skin. Raise any infection history with the provider before placement.

Complications of the pressure catheter

Uterine perforation is rare and is usually linked to extramembranous or improper placement. Placental abruption or injury to a placental vessel is also possible. Clues include vaginal bleeding, persistent uterine hypertonicity or sudden fetal bradycardia soon after insertion, and an absent pressure waveform while the uterus is clearly contracting. Extramembranous placement is not unusual and is often harmless, but it increases the risk of perforation.

The nurse confirms fluid appears in the catheter after placement and that the waveform matches palpated contractions. If bleeding, hypertonicity or a sudden heart rate drop follows insertion, notify the provider immediately; the catheter may need removal. Monitor maternal temperature, because intra-amniotic infection and endometritis are associated risks.

Scalp electrode injuries and a hypothetical question

Scalp electrode complications include small scalp lacerations, ulcers, haematoma and local abscess, and rarely deeper infection. After birth, inspect the attachment site, document its appearance and teach parents to report redness, swelling or discharge. A superficial site infection warrants follow-up because serious infections, though rare, have been reported.

Consider a hypothetical labouring patient with intact membranes, a poor external tracing and a history of recurrent genital herpes. Options include applying a scalp electrode now, placing a pressure catheter now, repositioning the external transducer and notifying the provider, or stopping monitoring. Repositioning and notifying is best: membranes are intact and the herpes history needs provider review. Applying either internal device would be premature, and stopping monitoring removes surveillance at the moment the tracing is already uncertain.

Documentation and safe use

Document the indication, the time of placement, who placed each device, membrane status and fluid characteristics, the waveform check and maternal temperature trends. Accurate records of membrane rupture time also matter for infection risk assessment later in labour and after birth. Tell the neonatal team that a scalp electrode was used so the attachment site is checked at the newborn assessment.

Confirm that the fetal heart signal is truly fetal rather than maternal by comparing it with the maternal pulse. Any device-related concern should be escalated rather than worked around, because switching off an alarm or accepting a poor signal can hide a deteriorating fetal condition.

Sources and further reading

MSD Manual Professional: Fetal monitoring during labor and delivery. Ruptured membranes and access through the cervix, use when external monitoring is inadequate and similar reliability of external and internal methods.

Case Reports in Obstetrics and Gynecology: Complications associated with insertion of intrauterine pressure catheters. Indications, placement away from the placenta, perforation, extramembranous placement, abruption, hypertonicity, infection and warning signs requiring removal.

Child's Nervous System: Neonatal brain abscess following fetal scalp electrode placement. Scalp ulcers, cephalohaematoma, scalp abscess and rare deep infections after scalp electrode use, and follow-up of superficial site infection.

Indian Journal of Sexually Transmitted Diseases and AIDS: Pregnancy and sexually transmitted viral infections. Fetal scalp electrodes as a port of entry and risk factor for neonatal herpes simplex infection.