Gestational age and birth weight centiles of singleton babies delivered normally following spontaneous labor, in Southern Sri Lanka

Aims: To estimate the gestational age and birth weight centiles of babies delivered normally, without any obstetric intervention, in women with uncomplicated singleton pregnancies establishing spontaneous onset of labour.

Method: Consecutive women with uncomplicated singleton pregnancies, attending the Academic Obstetrics and Gynecology Unit of the Teaching Hospital Mahamodara Galle, Sri Lanka, with confirmed dates and establishing spontaneous onset of labor and delivering vaginally between gestational age of 34 - 41 weeks, without any obstetric intervention , during the period September 2013 to February 2014 were studied. The gestational age at spontaneous onset of labor and vaginal delivery and the birth weights of the babies were recorded.

Results: There were 3294 consecutive deliveries during this period, and of them 1602 (48.6%) met the inclusion criteria. Median gestational age at delivery was 275 days (range 238-291 days, IQR 269 to 280 days) and the median birth weight was 3000 g (range1700g - 4350g; IQR 2750-3250g). The 10th, 50th and 90th birth weight centiles of the babies delivered at a gestational age of 275 days were approximately 2570g, 3050g and 3550g respectively.

Conclusions: The median gestational age among women with uncomplicated singleton pregnancies who established spontaneous onset of labor and delivered vaginally, without any obstetric intervention, was approximately five days shorter than the traditionally accepted 280 days. At a gestational age of 275 days, the mean birth weight was approximately 3038g and the 50th centile of the birth weight of the babies delivered was approximately 3050g.