Evaluation of the Fetal Response to Intrapartum Digital Fetal Scalp Stimulation to Identify Intrapartum Fetal Hypoxia.

The goal of intrapartum care is to ensure excellent maternal and perinatal outcomes. Normal labor is characterized by regular uterine contractions, which cause repeated transient interruptions in fetal oxygenation. Most fetuses tolerate this process well, but some do not. The fetal heart rate (FHR) pattern helps distinguish the former from the latter, as it is an indirect marker of fetal cardiac and central nervous system responses to changes in blood pressure, blood gases, and acid-base status. The term "suspected fetal compromise or risk of loss of fetal well-being" is used in obstetrics, when the fetus is considered to be at increased risk of ischemic hypoxic injury, brain damage or death, and is one of the most common indications for emergency cesarean section during labor. In our setting, continuous electronic fetal heart rate monitoring recorded by cardiotocography (CTG) is routinely used in labor to identify fetuses that may be at increased risk of compromise and may benefit from further evaluation of fetal well-being or other interventions. CTG tracings display the fetal heart rate (FHR) pattern along with maternal uterine activity.

CTG patterns are classified into discrete general categories according to four criteria: basal FHR, heart rate variability, presence or absence of FHR accelerations, and decelerations. An example of such a classification system is the 2015 FIGO International Federation of Gynecology and Obstetrics guideline, on which the investigators will base our study. The Spanish Society of Gynecology and Obstetrics defines the registry in normal, suspicious, and pathologic categories. Regardless of the classification system used, abnormal FHR patterns that do not respond to basic intrauterine resuscitation measures require further evaluation of fetal well-being and/or termination of pregnancy, either by cesarean section, assisted vaginal delivery, or spontaneous vaginal delivery.

CTG has a high false-positive rate for fetal compromise (60%) and the studies of Chandraharan et al are gaining momentum, where intrapartum interventions should be based on a thorough understanding of the features observed on the tracing recordings to differentiate normal fetal response to continued stress from the onset of compensation, so that timely action can be taken to avoid hypoxic ischemic encephalopathy and prenatal deaths, while avoiding unnecessary intrapartum interventions to the mother. Cesarean section rates are increasing worldwide, much of that increase is due to primary cesarean sections among nulliparous women due to emergency procedures in labor. Our great challenge is to achieve a reliable test of fetal well-being during labor and to be able to be minimally invasive for both mother and fetus.

When a suspicious or pathologic FHR pattern is detected and immediate delivery is not warranted, further evaluation of fetal well-being is necessary; such second-line evaluations or tests include fetal scalp blood, in Spain Gold standard to identify fetuses with acidosis and reduce the false positive rate of CTG, and digital fetal scalp stimulation. Clinical guidelines support the use of digital fetal scalp stimulation but also note that research evidence is limited. Digital fetal scalp stimulation is the least invasive method, as it does not require instruments; it involves rubbing the surface of the fetal scalp with pressure for 30 to 60 seconds; the response to stimulation should be evident in cardiotocographic patterns over the next 10 minutes, using a 5-minute average. Fetal scalp stimulation should elicit an acceleration of FHR defined as an increase in FHR ≥ 15 bpm for at least 15 seconds or normal FHR variability (5 to 25 bpm), or both. The presence of an acceleration of FHR or an increase in variability (when previously reduced), or both, is interpreted as a positive response, comparable to a normal fetal scalp blood pH result greater than 7.20.

Fetal scalp blood sampling is an intrapartum procedure to assess the presence and degree of fetal acidemia by analyzing fetal capillary blood for pH or lactate, as both give similar results, with pH being the gold standard test for fetal acidosis in our setting. An amnioscope with a light source is used to expose the fetal scalp, which is cleaned with a 2% aqueous chlorhexidine gauze from blood, mucosa and amniotic fluid, then the scalp is punctured with a 2 mm blade. The blood is collected in long capillary tubes. The test requires the cervix to be dilated at least 2 to 3 cm, can be difficult to perform and may be uncomfortable for the laboring woman. It is contraindicated when the mother is known to have a serious transmissible infection, such as HIV or hepatitis, and in fetuses at increased risk of hemorrhage. Rare complications described in case reports include infection, hemorrhage and cerebrospinal fluid leakage. The procedure will result in stimulation of the fetus, but the primary intent is to collect a scalp blood that will allow quantitative analysis of fetal pH or lactate, reflecting fetal blood oxygenation.

It is not taken into account that the scalp skin is a nonessential peripheral tissue that undergoes catecholamine-induced vasoconstriction early in the fetal stress response and therefore fetal scalp blood sampling does not reflect oxygenation of the fetal central organs and alkaline amniotic fluid and bile acids from meconium may alter results. It has also been shown that fetal scalp blood has no significant effect on the cesarean section rate in women monitored by continuous cardiotocography. Intrapartum fetal scalp blood sampling to measure pH, base excess or deficit, or lactate has not been clearly demonstrated to reduce emergency cesarean deliveries or operative vaginal deliveries or to improve long-term perinatal outcome.

For this reason and many others, such as quality control problems, cost, patient discomfort, sample failure rates of up to 10% and the lack of availability of sampling kits, fetal scalp blood sampling is only rarely performed in the United States and other countries, which is not currently the situation in Spain, since for the SEGO it continues to be the gold standard for detecting fetal acidosis.

The NICE 2022 guideline conducted a review comparing fetal blood sampling with digital fetal scalp stimulation and noted that the studies conducted to date were of low to very low quality, similar to the Cochrane 2023 review which includes two studies Hughes 2022 and Tahmina 2022 , in which Hughes compares fetal scalp stimulation and cardiotocographic patterns with fetal scalp blood samples and cardiotocographic patterns and Tahmina compares fetal head stimulation and cardiotocographic patterns with no fetal head stimulation intervention. The Hughes study reported an apgar score of less than 7 at 5 minutes, a finding that was not recorded in Tahmina, which reported a lower risk of cesarean section in the fetal scalp stimulation group, but again both studies are of very low quality. Although not included in the NICE or Cochrane review, there are other studies that demonstrate that the effectiveness of fetal scalp stimulation is poor for ruling out or confirming fetal hypoxia during labor.

Therefore, very low certainty evidence is available that makes it unclear whether fetal scalp stimulation is a safe and effective way to confirm fetal well-being during labor. Current studies have limitations. More high quality studies with sufficient sample size are needed to evaluate this research question. There is an ongoing study (FIRSST) that will be added to the NICE review in a later update.

The current project aims to give value to a second tier test with little demonstrated scientific evidence, fetal scalp stimulation.

• Differences in the cardiotocographic pattern of fetuses with digital fetal scalp stimulation vs. fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in the results of intrapartum fetal scalp blood of fetuses with digital fetal scalp stimulations versus fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in newborn ph results of fetuses with digital fetal scalp stimulations versus fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in the first minute apgar scores of the newborns in fetuses with digital fetal scalp stimulations versus fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in apgar scores at 5 minutes of life of newborns in fetuses with digital fetal scalp stimulations versus fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in the results of the type of newborn resuscitation in fetuses with digital fetal scalp stimulations versus fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in neonatal unit admission rates in fetuses with digital fetal scalp stimulations versus fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in newborn seizure percentages in fetuses with digital fetal scalp stimulation vs. fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in the percentages of newborn deaths in fetuses with digital fetal scalp stimulation vs. fetuses without digital fetal scalp stimulation [Time frame: 2 years]
• Differences in completion of cesarean delivery in fetuses with digital fetal scalp stimulation versus fetuses without digital fetal scalp stimulation. [Time frame: 2 years]
• Differences in instrumental deliveries in fetuses with digital fetal scalp stimulation versus fetuses without digital fetal scalp stimulation. [Time frame: 2 years]
• Differences in vaginal deliveries in fetuses with digital fetal scalp stimulation versus fetuses without digital fetal scalp stimulation. [Time frame: 2 years]