Background
Despite the widespread use of oxygen (O
2
) in intrauterine resuscitation, the obstetric scientists’ understanding of O
2
therapy is full of contradictions. We tested the hypothesis that higher maternal arterial partial pressure of oxygen (PO
2
) is associated with higher umbilical cord venous PO
2
(UvPO
2
).
Methods
This is a planned secondary analysis of a randomised controlled trial (RCT), 443 normal women were 1:1 randomly allocated to receive 2 L/min O
2
or room air from the onset of second stage to delivery. We reported that maternal 2 L/min O
2
exposure cannot affect the umbilical cord arterial pH or the fetal heart rate (FHR) pattern. In 217 non-random samples, we found 2 L/min O
2
exposure increased the maternal arterial PO
2
to the median 150 mmHg (hemoglobin would be saturated). The primary outcome for this analysis was UvPO
2
in these non-random samples.
Results
There were no significant differences between the O
2
group (
N
= 107) and the control group (
N
= 110) in the UvPO
2
(median 30.2, interquartile 25.4–35.2 versus median 28.3, interquartile 23.4–35.3, mmHg,
P
= 0.379). There were also no significant differences between room air and different percentiles of O
2
exposure duration (< 25th, ≧ 25th < 50th, ≧ 50th < 75th, ≧ 75th percentile) in the UvPO
2
.
Conclusions
Maternal O
2
exposure at super-physiological levels (median arterial blood PO
2
150 mmHg) in normal labor may not change the UvPO
2
.
Clinical trial registration
ClinicalTrials.gov
NCT02221440
, first posted in 20 August 2014.