The effect of labor on the acid-base status of the newborn

Abstract

We find no correlation between duration of the first stage of labor and umbilical artery pH or base excess. We do find a correlation between duration of the second stage of labor and the umbilical artery pH and base excess. However, a prolongation of the second stage with as much as three hours would give an expected lowering of the umbilical artery pH with only 0.05 and of base excess with 2.1 mmol/l for vaginal nulliparas and correspondingly with 0.09 and 3.9 mmol/l in women with previous vaginal births. This effect on pH and base excess is so small that it is hardly clinically relevant and we do not find any support for the belief that a long labor -- in the absence of other risk factors -- is to the disadvantage of the fetus.

The prognostic impact of a prolonged second stage of labor on maternal and fetal outcome

“…This hypothesis was supported by an extensive series of 25 069 deliveries documented in the North West Thames Health Region, England, in 1988, which, after adjusting for confounding factors, showed no relation between infant morbidity or mortality and the duration of the second stage was shown (21). This observation has been further confirmed by a recent Swedish study (17) and is basically consistent with the present study. However, evidence of a more frequent use of face masks and oxygen supplementation in newborns after a prolonged second stage of labor might indicate an increased potential of distress of the newborns which may not necessarily be reflected in the pH-levels.…”

“…The introduction of the policy of active management of labor, however, not only failed to reduce the rate of cesarean section (14) but also probably has even increased the rate of operative obstetrical interventions (15), without being cost-C Acta Obstet Gynecol Scand 81 (2002) effective (16). Because recent reports found no support for the early dogma that long labor is a disadvantage to the fetus (17,18) if adequate modern fetal monitoring is provided, many obstetricians returned to a less interventionist attitude towards prolonged second stage of labor. Concerns about potential hazards to the infant from a second stage Ͼ2 hr were initially provoked by the British Perinatal Mortality Survey of 1958, which showed an increase in perinatal mortality in cases with prolonged second stage (19).…”

Benefits of introducing universal umbilical cord blood gas and lactate analysis into an obstetric unit

“…The improvements in blood gas distributions cannot be explained by changes in the length of labour. Although associations between increasing duration of the second stage of labour and decreasing umbilical artery pH and increasing lactate levels have been described previously, 14–19 we found no change in the second stage duration across the study (Table 2). Furthermore, the increase in the length of the first stage of labour in this study was unlikely to have a beneficial effect on umbilical cord blood gas values.…”

Prolonged second stage of labor is associated with low Apgar score

“…Most previous studies report no association between the duration of second stage of labor and adverse infant outcomes, such as low Apgar scores at 5 min [17][18][19][20] or umbilical cord acid-base status [21,22]. However, a low Apgar score at 5 min is a rare outcome and all the above mentioned studies were underpowered to detect any associations of realistic magnitude.…”