We sampled 599 eligible healthy late preterm infants from 795 preterm infants who were born in January 2014 to April 2017 and got regular health care service in Child Health Care Center. Ethical approval was obtained from the Research and Ethics Committee of Shandong Qianfoshan Hospital before commencement. For all eligible infants, an informed consent was obtained from the parents before enrollment.
The criteria for inclusion and exclusion were as follows: ①PMA at birth: Late preterm birth, defined as 34–36 completed weeks of gestation calculated by last menstrual date, confirmed by early ultrasound measurements; ②No severe neonatal complications: Infants with any neonatal complications(such as severe neonatal asphyxia, hypoxic-ischemic encephalopathy, intracranial hemorrhage, respiratory distress syndrome, necrotizing enterocolitis, etc) which needed parenteral nutrition and intravenous fluid therapy were excluded; ③No congenital malformations and syndromes;④PMA at visit(week): Calculated as PMA at birth(week) + (Date of visit - Date of birth)/7. As the end time-point of this study—PMA at visit should be strictly at 40 weeks(term-corrected age), but it was difficult to control in practice. For better controlling the possible bias, we set the PMA at visit in the range of 37.7–42.3 weeks, equivalent to ±0.5 month chronological age(CA) from the expected date of delivery. Infants with PMA at visit beyond this range were excluded. The flow chart of the recruitment of healthy late preterm infants was shown in Fig.1 .![]()
The criteria for inclusion and exclusion were as follows: ①PMA at birth: Late preterm birth, defined as 34–36 completed weeks of gestation calculated by last menstrual date, confirmed by early ultrasound measurements; ②No severe neonatal complications: Infants with any neonatal complications(such as severe neonatal asphyxia, hypoxic-ischemic encephalopathy, intracranial hemorrhage, respiratory distress syndrome, necrotizing enterocolitis, etc) which needed parenteral nutrition and intravenous fluid therapy were excluded; ③No congenital malformations and syndromes;④PMA at visit(week): Calculated as PMA at birth(week) + (Date of visit - Date of birth)/7. As the end time-point of this study—PMA at visit should be strictly at 40 weeks(term-corrected age), but it was difficult to control in practice. For better controlling the possible bias, we set the PMA at visit in the range of 37.7–42.3 weeks, equivalent to ±0.5 month chronological age(CA) from the expected date of delivery. Infants with PMA at visit beyond this range were excluded. The flow chart of the recruitment of healthy late preterm infants was shown in Fig.
Flow chart showing the recruitment of healthy late preterm infants
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