The successful transition from fetal to neonatal life is a major physiological challenge that
requires the coordination of lung developmental processes, which culminate with the formation
of a diffusible alveolar-capillary barrier, adequate pulmonary vasoreactivity, mature
surfactant system, and clearance of lung fluid. During fetal life, gas exchange does not take
place in fetal lungs but in the placenta. High pulmonary vascular resistance diverts blood
flow to the left atrium through the foramen ovale and to the aorta via the ductus arteriosus.
The placental circulation receives 30-50 % of the fetal cardiac output and is the major
source of venous return to the fetal heart. Therefore, the umbilical venous return determines
the preload for the left ventricle. Shortly before birth and during labor, the lungs undergo
important transitional changes. The reabsorption of lung fluid within the airways is
initiated during labor by adrenaline-induced activation of sodium channels. Uterine
contractions during labor and the onset of inspiration after umbilical cord clamping generate
a high transpulmonary pressure gradient leading to additional clearance of fluid from the
airways into the surrounding tissue . Following the first breath and lung aeration,
oxygen-induced vasodilation leads to a sudden rise in pulmonary blood flow and left atrial
pressures, which closes the foramen ovale. Meanwhile, systemic vascular resistance increases
above the level of pulmonary vascular resistance after placental removal, which reverses
blood flow across the ductus arteriosus and induces ductal closure in response to high oxygen
tension.
The route of delivery can impact the success of adaptation to extrauterine life. Over the
past 30 years, the rate of cesarean deliveries has increased worldwide. In Belgium, this can
be as high as 20% of all deliveries. A subset of cesarean deliveries is scheduled in term
infants in the absence of spontaneous labor when vaginal delivery is considered as too risky
for maternal and/or child health. The so-called iterative cesarean delivery, which is usually
considered as a routine and harmless option, can however alter neonatal health. By contrast
with vaginal delivery, infants born at term by iterative cesarean delivery have to adapt
despite larger volumes of fluid within airways and interstitial tissue resulting from a
limited rise in transpulmonary pressure and adrenaline-induced fluid reabsorption.
Subsequently, the retention of lung fluid is responsible for transient tachypnea of the
newborn, a respiratory distress that is usually considered as mild, transient, and without
sequelae. Moreover, infants born by elective cesarean delivery exhibit a higher risk of
positive pressure ventilation resuscitation at birth, admission to the neonatal intensive
care unit (NICU), and severe hypoxic respiratory failure requiring mechanical ventilation in
the most severe cases. In addition to increased neonatal morbidity, iterative cesarean
section can impact mother-infant relationship. After vaginal delivery, immediate skin-to-skin
contact during the first minute after birth is the natural process recommended to support
mother-infant bonding and promote early onset of breastfeeding. Despite efforts made to start
skin-to-skin contact as early as possible after cesarean delivery, immediate contact is
practically difficult to implement. In our institution, the infant is usually shortly
separated from the mother after umbilical cord clamping to provide first care by a
pediatrician before returning on the mother's chest or on the father's chest depending on
parental wishes and maternal well-being during the operation. The separation between the
mother and her newborn can be further extended in the case of NICU admission for transient
tachypnea.
Beside the route of delivery, the timing of umbilical cord clamping can profoundly affect the
process of neonatal cardiorespiratory transition. Immediate cord clamping reduces the venous
return to the heart, which transiently decreases heartbeats, cardiac output and cerebral
blood flow before respiration initiates and pulmonary blood flow increases. Delayed cord
clamping for longer than 60 seconds improves the transfusion of blood from the placenta to
the newborn. Moreover, it can increase neonatal hemoglobin levels, improve long-term iron
stores, and improve neurodevelopmental outcomes. Nevertheless, in both clinical research
setting and daily practice, delayed cord clamping lasts rarely more than one minute during
cesarean section. More recently, another approach, referred to as physiologically based cord
clamping (PBCC), has been proposed to delay cord clamping up to 5 minutes after the onset of
ventilation. PBCC allows to start lung aeration while on placental support and, therefore,
promotes hemodynamic transition by increasing pulmonary blood flow and maintaining left
ventricle preload. This strategy has been demonstrated efficient in preterm lambs and is
feasible in very preterm infants, via the use of a purpose-designed resuscitation table that
allows delayed cord clamping, maintenance of body temperature, and concomitant respiratory
support where necessary. First experience has reported good parental acceptance of the
procedure. Because PBCC has not been reported in term infants at risk of respiratory distress
after birth, the present project aims to assess whether PBCC in term infants born by elective
cesarean section would not be inferior to standard umbilical cord clamping with regards to
adaptation to extrauterine life, respiratory morbidity, quality of mother-infant bonding, and
maternal safety.