Umbilical cord blood gas analysis

BMJ 2010; 340 doi: http://dx.doi.org/10.1136/bmj.c1720 (Published 13 May 2010) Cite this as: BMJ 2010;340:c1720
  1. James P Neilson, professor of obstetrics and gynaecology
  1. 1University of Liverpool, Liverpool L8 7SS
  1. jneilson{at}liv.ac.uk

    Paired samples should be analysed in selected circumstances

    The umbilical cord, discarded without thought from labour wards for so long, has recently generated interest on several fronts. Cord blood is a source of stem cells and some parents want cord blood collected for banking by commercial enterprises in case it can help their child’s future health needs. However, the Human Tissue Authority in the United Kingdom has recently expressed concerns about the safety of collection mechanisms.1 It is also increasingly recognised that obstetricians and midwives often clamp the cord too soon after birth, thereby depriving the baby of substantial amounts of blood—this is particularly important in parts of the world where infant anaemia is prevalent.2 And now we have biochemical analysis of cord blood. In the linked systematic review (doi:10.1136/bmj.c1471), Malin and colleagues assess the association between umbilical cord pH at birth and outcomes.3

    Umbilical cord blood gases could be of value in auditing the outcomes of labour, predicting future development of the newborn, helping clinical research, and resolving expensive medicolegal disputes. If the fetus is deprived of adequate oxygenation during labour—for example, through placental malfunction, cord compression, or excessive uterine contractions—the pH drops and the base deficit rises as anaerobic metabolism is activated and lactic acid is produced. Babies with limited metabolic reserve, notably the preterm fetus and those with restricted growth, are less able to withstand the effects of hypoxaemia. However, the clinical guideline from the National Institute for Health and Clinical Excellence in 2007 on intrapartum care was lukewarm about the prognostic importance of low umbilical artery pH values—“cord arterial gas was not regarded as a good predictor of either neonatal death or developing cerebral palsy, even compared with Apgar scores.”4

    In contrast, Malin and colleagues’ systematic review of observational data suggests that a strong association exists between low umbilical artery pH at birth and major adverse outcomes including death, hypoxic ischaemic encephalopathy (usually manifesting as neonatal seizures), potentially serious brain abnormalities identified by imaging (periventricular leucomalacia or intraventricular haemorrhage), and cerebral palsy.3

    Malin and colleagues have been at the forefront of systematic reviews of screening and diagnostic tests in the perinatal field. In their systematic review they included 51 studies that, in total, described the outcome for almost half a million babies with known cord blood gas results. Most studies reported umbilical artery pH values but fewer data were available for venous pH or for base deficit. Fifteen studies reported long term outcomes with a median follow-up of five years. The quality of the studies varied, but quality did not seem to influence results on meta-regression. Further research is needed to refine the prognostic relevance of values in individual cases and to clarify the added value of base deficit, in addition to arterial pH.

    Ultimately, given the findings of this study, we should aim to reduce the number of babies born with a low cord pH, without increasing unnecessary obstetric intervention. Hopefully this can be achieved by more hands-on input to labour ward care by fully trained obstetric specialists.5 The use of computerised intelligent systems to guide decision making by obstetricians and midwives might also help. The INFANT trial will assess whether outcome is improved by use of an intelligent system during labours in which cardiotocographic monitoring of the fetus has been undertaken. Cord artery pH less than 7.05 with base deficit greater than 12 mmol/l will be an important secondary outcome.6

    In the meantime, the NICE recommendations that, “Paired cord blood gases do not need to be taken routinely. They should be taken when there has been concern about the baby either in labour or immediately following birth” remain valid.4 US guidelines are most explicit and recommend taking paired samples from all babies born by caesarean section because of fetal compromise, low five minute Apgar scores, severe fetal growth restriction, abnormal fetal heart tracing, maternal thyroid disease, intrapartum fever, and all multiple births.7 “Pairing” refers to sampling of both umbilical artery blood and vein blood. Different values confirm that the umbilical artery (blood direct from fetus) has been sampled separately from the more easily accessed vein (blood from placenta). If delayed cord clamping is practised, as it should be, as well as cord blood gas sampling, times should be carefully noted because the blood gas results will change with time.8 9


    Cite this as: BMJ 2010;340:c1720


    • Research, doi:10.1136/bmj.c1471
    • The author has completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declares (1) no support from any commercial entity for the submitted work; (2) no relationship with any company that might have an interest in the submitted work in the previous three years; (3) no spouse, partner, or children with financial relationships that may be relevant to the submitted work; and (4) no non-financial interests that may be relevant to the submitted work.

    • Provenance and peer review: Commissioned; not externally peer reviewed.