Assessment of the umbilical cord gases at birth is an objective measurement of the neonatal condition. However, previous studies have shown that the results are unreliable in one out of four paired samples. The aim of our study was to assess the sampling of cord gases after operative deliveries. We found out that the error rate in our unit was 39% and the erroneous sampling was more common in arterial samples and in deliveries that happened during the night. We believe that assessment of the results obtained from paracentesis of the umbilical vessels helps to evaluate the quality of the sampling and to identify preventable causes of error.