Andrew Farkas
Consultant Obstetrician and Gynaecologist
Jessop Wing
Tree Root Walk
Sheffield S10 2SF
United Kingdom

Stephan Schmidt
Chairman and Director of Department
Department of Obstetrics and Perinatal Medicine
University of Marburg
D-35037 Marburg
Germany

Please introduce your departments

• 6,000 deliveries per annum
• The caesarean section rate is approximately
  22 %, of which two thirds are emergency procedures
• 22 Consultants including the interviewee
• 16 Specialist Registrars and 180 midwives 
• Special Care Baby Unit of 30 cots, of which 12 are
  intensive care cots
• Both the Obstetric and Neonatal Units are tertiary
  referral centers, which accept in-utero transfers
  of obstetric patients and ex-utero transfers of
  neonates from within the region

• 1,200 deliveries per annum
• 80 % are risk cases, including 20 % of premature births
• The caesarean section rate is approximately 27%
• In low risk cases, the caesarean section rate is 11 %
• Four consultants, eight residents, 17 midwives and 22 nurses
• The unit provides maximum-level perinatal care

What are the indications for cord gas sampling?

Practice varies concerning the indications for cord blood gas analysis at delivery. 10 % of units performed cord gas analysis on all deliveries but 16 % on none [4].

Indications for selective, as opposed to universal, cord blood gas analysis include caesarean section, instrumental deliveries, deliveries where fetal distress is suspected and delivery is complicated by meconium-stained fluid.

The ACOG Guidelines suggest that cord blood gas analysis should be performed if the 5-minute Apgar score is depressed [1]. 

A specific value is not given. In our unit, cord sampling is recommended if the Apgar score at five minutes is seven or less. 

In practice, cord gas analysis is often performed if there is suspicion of fetal distress at delivery. 

In Germany, cord blood values are part of the features of external quality control (Social law 2002(§ 137)).

Umbilical artery samples are analyzed in >95 % of cases in the majority of hospitals in my region. 

The percentage of obstetric units performing cord sampling has risen over the past 20 years from some 80 % to near 100 %.

Obstetrics in Germany is the field with the highest frequency of lawsuits as compared with other medical specialties. 

Since pH values will reduce the burden of malpractice, sampling and documentation are enforced. 

Storage of the documents of blood gas measurements are proposed to be 30 years for medico-legal reasons.

How are samples taken?

Umbilical cord blood analysis (UCBA) is performed on samples taken following birth from a double-clamped segment of the umbilical cord.

In the UK, 54 % of units performing the analysis sampled both arterial and venous blood and 18 % sampled venous blood only [4].

The ACOG Guidelines suggest that a clamped segment of cord is stable for pH and blood gas assessment for at least 60 minutes. 

In practice, blood gas analysis should be performed within 20 minutes.UCBA is performed on samples obtained from the cord with a preheparinized syringe and needle.

Arterial samples are routinely taken directly after birth. 

It is recommended to collect the samples with the artery still pulsating, in order to be sure of analyzing arterial blood. 

Most hospitals in my region perform additional venous sampling if late clamping is performed.

Heparin-coated capillary tubes are most commonly used. Cord sampling by syringes are rarely performed.

Samples should be measured immediately in order to be able to repeat sampling right after expulsion of the placenta from chorionic vessels, if necessary.

Who performs the cord sampling?

Umbilical blood samples are usually taken by midwives and processed by trained personnel, including midwives. 

Doctors performing an operative vaginal delivery or caesarean section may sometimes take the samples. 

In some units, operating department practitioners (ODPs) take the samples and in others support workers have been trained to take the samples and process them through the blood gas analyzer.

Midwives usually take the umbilical blood samples.

Doctors supervise the analysis, which is usually performed by midwives or technicians.

How do you ensure good quality of the sample?

The most common problem is that samples are obtained from the umbilical vein. 

Samples are harder to obtain from the umbilical artery, which is of a narrower caliber. 

Paired samples should be obtained in order to analyze gases from both vessels and to ensure that they have both been sampled.

In practice, resampling is rarely performed. It should be performed if a clear result is not obtained from the original sample(s).

In our unit, the incidence of samples rejected by the blood gas analyzer have been reduced by introducing a training package for all midwives 

With proper training, I estimate a 95 % success ratio of obtaining both arterial and venous samples.

Contamination with air is detected during evaluation of pO₂ (>30 mmHg) or pCO₂ (<45 mmHg). In these cases, the doctor will ask for a repeated sample.

Which parameters are measured?

In our unit, a full blood gas analysis is performed, including pH, pCO₂, pO₂, bicarbonate and base excess. 

In the UK, 24 % of units performing UCBA analyzed pH only. 

Notwithstanding that a full blood gas analysis is performed, obstetricians often consider and document only pH and base excess. 

Until this year pH has been the only feature of obligatory documentation, but now base excess (BE) is discussed as a parameter for quality control as well. 

Clinical interpretation of the results requires the examination of pCO₂ and base deficit of the extracellular fluid from each vessel, as well as pH.

What action can be taken based on a UCBA result?

There is very little specific neonatal intervention. 

However, it may inform the neonatal pediatrician as to the risk of the neonate and where it should be nursed. This should lead to appropriate observations and reduction of complication such as hypoglycemia.

It also gives the neonatologist a baseline of the baby’s acid-base balance at birth. Fetal acidemia recovers very quickly postnatally. 

There is little indication for repeating blood gases in the neonate, unless clinically indicated.   

The interpretation of blood gas values is part of a total evaluation with additional focus on the Apgar score.

The clinical action based on pH measurements includes an intensified observation of all newborns with pH values below 7.10.

Newborn with pH < 7.00 should be transferred to intensive care units even if normal Apgar score is reported.