Objective To study the influences of biological factors on umbilical artery blood gas (UABG) of the newborns and to establish the normal UABG range.Methods From March 2008 to September 2009,all newborns without anomalies whose 1 min Apgar score ≥ 8 born in six hospitals in China were consecutively enrolled into this study.Umbilical cord and blood samples were collected with standardized method.pH value,PO2,PCO2 and base excess (BE) of umbilical artery were detected by uniformed blood gas analyzer.The influences of biological factors,such as parity,fetal number,gender,gestational age,birth weight,relationship of birth weight to gestational age,and delivery mode on UABG were analyzed by analysis of variance (LSD test) and two-independent sample t test.Based on the investigation results,normal range of UABG of the newborns was established after ruling out biological influence factors.UABG reference values were expressed as (x)± 1.96s.Results Totally 20605 newborns were born in the six hospitals during the study period,among which 20191 newborns were enrolled in this study.Gender had no significant influence on UABG parameters (P>0.05).pH (7.19±0.10) and BE [(-7.75±3.03) mmol/L] of newborns of primiparous were lower than those born from multiparous (P<0.05).BE of second babies[(-7.60±3.02) mmol/L]was lower than that of babies born from mothers of more than three parities (P<0.05).Compared to twins [PO2(2.91±1.21) kPa,PCO2 (7.18±1.43) kPa and BE (-6.84±3.26) mmol/L],the PO2 of singletons was higher [(3.16±1.24) kPa,t=3.612,P<0.05],and PCO2 [(7.01± 1.65) kPa,t=2.092,P<0.05] and BE [(-7.65 ± 3.11) mmol/L,t=2.930,P<0.05] were lower.As gestational age increased,the value of pH,BE and PO2 decreased,and PCO2 increased (P<0.05,respectively).pH and BE of low birth weight infants were higher than those of normal birth weight infants and macrosomia (P<0.05 respectively).pH,BE and PO2 of small for gestational age infants were lower than those of appropriate and large for gestational age infants,while PCO2 was higher (P<0.05 respectively).pH.PO2 and BE of cesarean scction group were higher than those of other delivery mode groups,while PCO2 was lower (P<0.05 respectively).PO2 and BE of forceps group were lower than those of normal delivery group,while its PCO2 was higher (P<0.05 respectively).After ruling out the influence factors,the normal ranges ((x)±1.96s) of UABG and BE of the 10645 singleton,term,normal delivered,normal birth weight,appropriate for gestational age,1 min Apgar score≥8,non anomalous newborns were (7.20±0.20) for pH,(-7.64±6.36) mmol/L for BE,(3.15±1.23) kPa for PO2 and (7.02±1.62) kPa for PCO2.Conclusions Many biological factors might affect UABG parameters.When using pH or BE threshold as one of the criteria for evaluation of birth asphyxia,the influences of biological factors should be considered. Key words: Umbilical arteries; Blood gas analysis; Reference values; Hydrogen-ion cincentration; Infant,newborn; Multicenter study
Read full abstract