Abstract
Objective:
We performed the present study to investigate the feto-maternal osmotic relationship at term with the hypothesis that, in contrast to the literature, maternal plasma osmolality is lower than fetal levels. In a previous study, we found that maternal plasma sodium at delivery was consistently lower than the sodium in the umbilical artery. Our aim was to corroborate these results with analysis of osmolality.
Methods:
Blood was sampled from 30 women immediately before cesarean section and from the umbilical artery and vein before cord clamping and osmolality, sodium and albumin were analyzed.
Results:
Maternal osmolality was (mean; 95% confidence interval) 287.0 (285.8–288.2) mOsmkg/kg, arterial cord osmolality was 289.4 (287.9–291.0) mOsm/kg and venous cord osmolality was 287.3 (286.0–288.5) mOsm/kg. The paired difference between maternal and umbilical arterial osmolality was mean (SD) −2.4 (3.3) mOsm/kg (P<0.001), between maternal and umbilical vein −0.3 (3.0) mOsm/kg (P=0.63) and between umbilical artery and vein −2.1 (2.8) mOsm/kg (P<0.001).
Conclusion:
Maternal osmolality was significantly lower than arterial cord osmolality confirming our previous results. The feto-maternal osmotic gradient favors water transport from the mother to the fetus and may increase the fetal risk of water intoxication when the mother ingests or is administered large volumes of electrolyte free solutions.
Acknowledgements
The authors would like to thank the mothers who participated in the study and are grateful to midwives, nurses and colleagues who patiently supported the study. Dr. K. Rockstroh and Dr. H Persson diligently collaborated in the execution of the study.
Author’s statement
Conflict of interest: Authors state no conflict of interest.
Material and methods: Informed consent: Informed consent has been obtained from all individuals included in this study.
Ethical approval: The research related to human subject use has complied with all the relevant national regulations, and institutional policies, and is in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.
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