2.1. Study design
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BLOOD, GROUP B
A total of 300 participants were selected from the UCB collected from a grade III public hospital between August 2018 and December 2021 according to the inclusion criteria. A previous trial found that the mean ± standard deviation of UCB volume was 74.73 ± 28.02. We hypothesized the mean of UCB volume were 70 and 74 as group A and B, standard deviation was 10. And calculated that a sample size of 78 patients per group would provide 80% power at Type I error rate value of 10% to detect the difference in UCB volume between 2 groups. To account for possible protocol violations, we enrolled a total of 100 participants each group. The inclusion criteria were as follows: maternal age 18 to 40 years, 37 to 42 weeks of gestation, vaginal delivery, singleton pregnancy, consented to donating or depositing cord blood, and availability of complete maternal information records. The exclusion criteria included non-vaginal delivery and partially missing test data. The women were randomly divided into 3 groups of 100 each by random selection method. Group A was defined as the group in which UCB samples for hematopoietic stem cell transplantation and blood gas analysis were collected. Group B was defined as that wherein UCB was collected for hematopoietic stem cell transplantation. Group C was defined as that wherein UCB was collected only for blood gas analysis. Hematopoietic stem cell transplantation-related indices were detected in groups A and B, and blood gas analysis was performed in groups A and C. The chief head nurse of the hospital generated the random allocation sequence, enrolled participants, and assigned participants to interventions. The analyst was unaware of the grouping.All cord blood samples were sent to the Guangdong Cord Blood Hematopoietic Stem Cell Bank (GDCBB) for UCB preparation, testing, and storage. All UCB samples were prepared in accordance with the requirements of relevant Chinese laws and regulations.