['To study the influence of gestational age on lactate concentration in arterial and venous umbilical cord blood at birth and to define gestational age-specific reference values for lactate in vigorous newborns.', 'Population-based comparative.', 'University hospitals.', 'Vigorous newborns with validated umbilical cord blood samples.', 'From 2000 to 2004, routine cord blood gases, lactate and obstetric data from two university hospitals were available for 17 867 newborns from gestational week 24 to 43. After validation of blood samples and inclusion only of singleton pregnancies aimed for vaginal delivery, 10 700 women remained. Among those, reference values were defined in 10 169 vigorous newborns, that is in newborns with a 5-minute Apgar score corresponding to the gestational age-specific median value minus 1 point score, or better.', 'Cord lactate concentration relative to gestational age.', 'The arterial and venous lactate concentrations increased monotonously with gestational age from 34 weeks. Considerable differences were found between mean and median values, but after logarithmic transformation the log-lactate values were normally distributed. Simple linear regression analysis showed a significant association between the log-lactate values and gestational age (P < 10(-6), R(2)= 0.024). Reference curves were constructed after anti-logarithmic transformation. Both the gestational age and the time of the second stage of labour influenced, independently of each other, the lactate concentrations.'] Is lactate concentration in umbilical cord blood gestational age-dependent : a population-based study of 17 867 newborns?