The investigators wished to determine whether estimating endotracheal tube (ETT) insertion depth using the formula given by Spanish guidelines recommendations (5,5 plus weight) rather than the depth using the formula given by international guidelines recommendations (6 plus weight) resulted in more correctly positioned endotracheal tube tips in newborns intubated in the delivery room.

A number of different methods have been used to guide clinicians in estimating the correct depth of insertion of endotracheal tube (ETT) at the time of oral intubation. Minor differences in tube length may lead to intubation of the right main bronchus or extubation. However, none of them has shown to be better than others when compared in the context of randomized clinical trials.

Commonly, clinicians use a formula based on the newborn's weight (Tochen formula: ETT insertion depth (cm)=6 + wt (kg)). While this method is widely used and recommended by international guidelines, it has been found to frequently result in incorrectly positioned tubes, especially in infants <1000 g in weight in whom it may lead to overestimation of ETT insertion depth.

On the other hand, Spanish Society of Neonatology recommended in their last published guidelines (2017) to use an alternative version formula (ETT insertion depth (cm)=5.5 + wt (kg)), which is commonly used among Spanish neonatal units.

Finally, no studies have been performed in newborns who require oral intubation in the delivery room, since these intubations are usually excluded because infants are not routinely weighed prior to resuscitation and weight can not be rapidly obtained. Given that Obstetric Unit in our hospital is a high standard one with a highly reliable estimated fetal weight in prenatal ultrasound, the investigators will use estimated fetal weight referred on ultrasounds or 50th percentile for gestational age for calculations.

Inclusion Criteria:

• All newborns requiring endotracheal oral intubation in the delivery room after birth.
• Parents accept deferred informed consent to participate in the study.

Exclusion Criteria:

• Prior to randomization
• Uncontrolled gestation where both estimated fetal weight and gestational age are unknown.
• Upper airway anomaly or a lung anomaly that would distort the upper airway anatomy.
• Infants who require nasotracheal intubation
• Infants who are intubated in the Neonatal Intensive Care Unit
• Post-randomization
• Newborns who are randomized but finally do not require intubation
• Intubated newborns who are electively extubated in the delivery room
• Parents / legal guardian refuse to give consent to participate in the study

Clinicians and neonatal nurses will not masked to group assignment. However, Neonatal Intensive Care Unit nurses who take care of the patient will be mask, as well as both pediatric radiologist who will determine the main outcome of the study.