Measuring placental transfusion for term births: weighing babies with cord intact.

OBJECTIVE

To estimate the volume and duration of placental transfusion at term.

DESIGN

Prospective observational study.

SETTING

Maternity unit in Bradford, UK.

POPULATION

Twenty-six term births.

METHODS

Babies were weighed with umbilical cord intact using digital scales that record an average weight every 2 seconds. Placental transfusion was calculated from the change in weight between birth and either cord clamping or when weighing stopped. Start and end weights were estimated using both a B-spline and inspection of graphs. Weight was converted to volume, 1 ml of blood weighing 1.05 g.

MAIN OUTCOME MEASURES

Volume and duration of placental transfusion.

RESULTS

Twenty-six babies were weighed. Start weights were difficult to determine because of artefacts in the data as the baby was placed on the scales and wrapped. The mean difference in weight was 116 g [95% confidence interval (CI), 72-160 g] using the B-spline and 87 g (95% CI, 64-110 g) using inspection. Converting this to the mean volume of placental transfusion gave 110 ml (95% CI, 69-152 ml) and 83 ml (95% CI, 61-106 ml), respectively. Placental transfusion was usually complete by 2 minutes, but sometimes continued for up to 5 minutes. Based on the B-spline, placental transfusion contributed 32 ml (95% CI, 30-33 ml) per kilogram of birth weight to blood volume, but 24 ml (95% CI, 19-32 ml) based on inspection. This equates to 40% (95% CI, 37-42%) and 30% (24-40%), respectively, of total potential blood volume.

CONCLUSION

Inspection of the graphs probably underestimates placental transfusion. For term infants, placental transfusion contributes between one-third and one-quarter of total potential blood volume at birth.