Foetal blood sampling in clinical obstetrics

Umbilical blood gas analysis: I. Effect of storage of samples on outcome

The pH and blood gas values of umbilical blood samples must be determined as soon as possible after birth to avoid changes in pH, oxygen pressure (PO2) and carbon dioxide pressure (PCO2). Since a continuous around-the-clock laboratory service is not available in every hospital, a method of reducing these changes is desirable. Determination of pH and blood gas values at different time intervals while the samples were stored on ice showed that pH decreased by a mean of 0.003 unit/hr, whereas PCO2 and PO2 increased. A method of reducing glycolysis in blood cells must be found to make postponement of analysis acceptable.

Lactic acidosis complicating treatment of ketosis of labour

Hypertonic glucose, fructose, and sorbitol solutions were given intravenously to women in the first stage of labour who had ketonuria and ketonaemia as evidenced by a raised blood acetoacetate and 3-hydrosybutyrate. There was no difference in the antiketogenic action of these, which was rapid and effective, but when compared with a control group who were given normal saline they had a high incidence of hyperlactataemia, and nine out of 28 patients developed lactic acidosis after the infusions. The "lactatogenic" effect was shared by all three substrates, and when they are used in the treatment of ketosis of labour, and the mother develops lactic acidosis, they might exacerbate pre-existing lactic acidosis and precipitate fetal distress.

Clinical significance of fetal heart rate patterns during labor. II. Late decelerations

Among a population of high-risk patients in labor who had continuous "direct" electronic monitoring, 147 presented late decelerations and 598 had no decelerations at the time the first stage was completed, or a cesarean section decided upon. A variety of clinical aspects of mother and fetus were analyzed, considering some alterations observed in the FHR pattern. Apgar scores were lower among decelerations, and there was a negative correlation between these two. Maternal pathology, other than PRM, was higher among decelerations and these required enhancement more often. There was very high association with tachycardia, saltatory, and fixed baseline among decelerations, and these infants were very often distressed and born depressed. Within the group of decelerations, small fetuses had lower Apgar scores. There was a negative correlation between number of decelerations and Apgar score. The small fetuses had a high incidence of tachycardia and fixed baseline, saltatory being almost absent. Their neonatal outcome was poor. A comparison of fetal response to distress was done considering age of gestation (premature, term, and postmature) and found to be different. The mechanisms involved in late deceleration are discussed, reviewing the published experimental work. When interpreting FHR patterns, age of gestation should be one of the most important considerations.

Correlation between the foetal acid-base status and the Apgar score

The foetal pH values of eighty-eight cases delivered within 30 min after foetal blood sampling were correlated with the 1-min Apgar score. With a pH of 7·20 or above the error of prediction was 1·3%. The error in cases with pH below 7·20 was 54·5%.

Significantly higher pH and lower δ base deficit were present in the low foetal pH group in vigorous, as opposed to depressed infants, suggesting that infusion acidosis was present in infants with a high Apgar score.

The degree of correlation between the foetal pH and the Apgar score was not significantly influenced by shortening the sampling-delivery interval to 15 min or lengthening it to 3 hr. The most significant factor affecting the degree of correlation in the present study was the setting of the critical pH. If the criterion of the critical pH was taken as 7·13 there would have been no false positive results and the error of prediction in cases delivered within 30 min of foetal blood sampling would be reduced to 1·1%.

Foetal blood sampling. Practical approach to management of foetal distress

The practical application of foetal blood sampling in the routine management of patients in labour has been reviewed in a six-month survey, during which time 1,668 patients were delivered at Queen Charlotte's Hospital.Foetal acidaemia (pH 7.25 or less) occurred in 45 of the 295 patients who showed clinical signs of foetal distress. Foetal tachycardia was the presenting sign in 33 of these 45 patients, underlining the importance of this physical sign. Foetal acidaemia in association with clinical foetal distress occurred twice as often in patients who had complications of pregnancy and who were therefore regarded as obstetrically "at risk" as it did in patients who were obstetrically "normal" No cases of acidaemia were detected in any of the foetal blood samples performed routinely on "at-risk" patients in the absence of clinical foetal distress.