Percentile curves for gestational age specific birth length of newborns

Objective To establish population-based centiles for gestational age specific birth length of newborns. Methods A total of 5 201 singleton, live-birth and without birth defects newborns in Shunyi District Hospital and Shunyi Maternal and Child Hospital from 1st November 2009 to 21st January 2011 were admitted into this study. The newborns were selected to take standard measurement of birth length and calculate the growth rate. K-median-coefficent of variation method was used to smooth the percentile curves. Comparison of birth length was made between different genders and parities. The study protocol was approved by the Ethical Review Board of Investigation in Human Being of Beijing Shunyi Hospital and Shunyi District Health Care Hospital for women and Child.Informed consent was obtained from each participants＇ parents. Results The gestational age of 5 201 newborns were from 26 to 44 weeks, and the average birth length was (49.48±1.87)cm. The average birth length of male newborns was (49.75±1.90) cm, which was (49.17±1.78) cm in female newborns.Significant differences of birth length were found between genders (t=11.345, P 0.05). Percentiles of birth length and growth rate were calculated, the curves for each gestational age were successfully smoothed, through which we found that birth length grew with the growth of the gestational age, and the growth rate of birth length decreased with gestational age growth among 37 to 41 weeks of gestation. Conclusions Recent percentiles for gestational age specific birth length of newborns were presented in this research, and it can be used as a birth length normative reference for the local clinicians. Key words: Gestational age; Birth length; Smoothed percentiles; Infant, newborn