The objective of the study is to investigate the FRI's ability to identify cases requiring urgent intervention which will present an adverse perinatal outcome (respiratory acidosis, metabolic acidosis, Apgar index, etc.) compared to the classical interpretation of CTG.

Patients whose CTG in labor will be considered non-reassuring will be enrolled and randomized into two groups. The "Fetal Reserve Index" algorithm will be applied to the first group of patients.

The second group of patients will, however, be managed according to the usual protocols internal management.

Patients in active labor and diagnosed with category II CTG will be enrolled and randomized into two groups. Full randomization will be performed by Excel software by generating random numbers using the "Randomise (RAND)" function The "Fetal Reserve Index" algorithm will be applied to the first group of patients. In in these patients the fetal reserve index will be calculated every 10 minutes. At each of the components of the score will be assigned a score of 1 if the variable evaluated is considered normal, 0 if classified as abnormal. The different scores obtained (score from 1 to 8) will be classified into 3 risk categories: Score 5-8: green zone, Score 3-4: zone yellow, Score 1-2: red zone. An FRI of 1-2 (red zone) is to be considered as anomalous. For patients with abnormal FRI a 40 minute timer will be started within which it will be necessary to exit the "red zone". If such patients will not be able to exit the red zone within 40 minutes, an additional timer will be started of 30 minutes within which the birth will be completed. The birth will be completed immediately in case of sentinel events (prolonged bradycardia, detachment of placenta, cord prolapse).

The second group of patients will, however, be managed according to the usual protocols internal management.

Inclusion Criteria:

• Women in the active phase of labor who presented when they entered the room I delivered a negative admission test (i.e. a normoreactive CTG according to ACOG) and that subsequently present during labor a diagnosis of category II CTG
• Single term pregnancy
• Signature of informed consent

Exclusion criteria

• Failure to sign the informed consent
• Previous caesarean section (TOLAC)
• Twin pregnancy
• Gestational age <37 weeks
• Known genetic/chromosomal syndromes and/or malformations, excluding heart disease without contraindication to vaginal birth

Exclusion Criteria:

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the essential criterion is pregnancy