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.研究目的：估算足月妊娠时胎盘输血（placental transfusion）的总量与持续时长。 研究设计：前瞻性观察研究。 研究场景：英国布拉德福德某产科病房。 研究对象：26例足月分娩病例。 研究方法：采用每2秒记录一次平均重量的数字秤，在脐带完整状态下对新生儿进行称重。通过新生儿出生时至脐带夹闭或停止称重时段的体重变化，计算胎盘输血（placental transfusion）量。分别采用B样条（B-spline）法与图像目视法估算起始与终止体重。将体重转换为容量时，按照1ml血液重1.05g的标准进行换算。 主要结局指标：胎盘输血（placental transfusion）的总量与持续时长。 研究结果：共对26例新生儿完成称重。由于新生儿放置于秤上及包裹过程中产生的数据伪影，起始体重较难准确测定。采用B样条（B-spline）法得到的平均体重差为116g[95%置信区间（confidence interval, CI）：72~160g]，采用图像目视法得到的平均体重差为87g（95%置信区间（confidence interval, CI）：64~110g）。将体重差转换为胎盘输血平均容量后，分别为110ml（95%置信区间（confidence interval, CI）：69~152ml）与83ml（95%置信区间（confidence interval, CI）：61~106ml）。胎盘输血通常可在2分钟内完成，但有时可持续长达5分钟。基于B样条（B-spline）法的计算结果显示，胎盘输血可使新生儿血容量增加32ml/kg出生体重（95%置信区间（confidence interval, CI）：30~33ml/kg），而基于图像目视法的结果为24ml/kg出生体重（95%置信区间（confidence interval, CI）：19~32ml/kg）。这分别相当于总潜在血容量的40%（95%置信区间（confidence interval, CI）：37%~42%）与30%（24%~40%）。 研究结论：图像目视法可能会低估胎盘输血的量。对于足月新生儿而言，胎盘输血可占出生时总潜在血容量的1/3至1/4。