The purpose of this study is evaluating the effectiveness of three-stair-position (TSP) on the rate of Apnea of Prematurity (AOP), the feeding performance and the vital signs.

Apnea of Prematurity (AOP) is common critical symptoms of preterm infants with great harm for prematurity. Recurrent apnea may lead to brain damage caused by hypoxia, affecting the nervous system, even threatening life (1, 2). Therefore, choosing an intervention which can prevent and reduce occurrence of AOP with fewer side effects is an important issue that should be closely watched by neonatal intensive care unit (NICU) health care.

Prone position is the forefront treatment due to its simple, economic and non-invasive. In clinic, it includes horizontal prone position (HPP), Head elevated tilt 15 ° prone position (HETP) and three-step-prone position (TSP)(3).Many studies have shown that HETP can allow thoracic volume increased and make abdominal movement more coordinated in preterm children, and then it is more favorable than the HPP on improving respiratory function. So HETP has been a routine position in NICU instead of HPP (4, 5). HETP, however, always make the babies slide to the foot of the bed resulting in airway obstruction. Therefore, scholars have proposed TSP which should prevent this phenomenon (6). In the study, the effectiveness of TSP on improvement of AOP will be evaluated trying to find a more suitable position for preterm infants.

Inclusion Criteria:

1. preterm, gestational age(GA) <34weeks determined by obstetric ultra-sonogram and clinical examination
2. steady vital signs
3. Apgar scores were greater than or equal to 3 at 1min and greater than or equal to 5 at 5 minutes.

Exclusion Criteria:

1. infants with congenital malformation，for example Congenital Heart Disease, Diaphragmatic hernia, Hirschsprung,etc
2. Infants who need special position and/or intervention (gastroschisis or umbilical catheterization)
3. weight<1000g
4. infants who were undertaking conventional invasive mechanical ventilation.