American Association for Clinical Chemistry
Better health through laboratory medicine


Reference Interval Corner

Sharon M Geaghan M.D.

Recent changes in obstetric practice: implications for laboratory specimens

Obstetric practice has varied widely in terms of the time before clamping the umbilical cord after delivery. The usual time of cord clamping after delivery may be 15-20 seconds. Delay of umbilical cord clamping provides additional placental transfusion to neonates, and can result in higher hematocrits. In preterm infants this is critically important, as frequent and extensive laboratory testing in neonatal intensive care units is the number one cause of blood loss and anemia. Overall, excessive phlebotomy ‘‘overdraws’’ in excess of the minimum requirement--a common occurrence in preterm infants—and typical weekly phlebotomy loss for a preterm infant during the first two weeks of life can be up to 30% of their total blood volume. Approximately the same volume is transfused to compensate for losses. RBC transfusions have the risk of incompatibility, suppression of the hematopoietic, transfusion reactions, viral infections, and, based on recent literature, poorer outcomes1.

Evidence base for delayed cord clamping

The American College of Obstetricians and Gynecologists (ACOG) and the American Academy of Pediatrics (AAP) have recently endorsed the practice of delay of cord clamping (30-60 seconds) for preterm infants. Widespread changes in obstetric practice follow ACOG guidance. The evidence base is a literature that has conclusively demonstrated that clamping the cord after 30-60 seconds increases circulating blood volume and red cell iron stores; reduces the incidence of anemia and therefore, the need for red blood cell transfusions. There is no current evidence base for delaying cord clamping after delivery of full term infants. Most importantly, the risk of intracranial bleeding is reduced approximately 50%.2

The number of newborns polycythemia increases with late cord clamping

To evaluate the effect of cord clamping time on outcomes, a randomized controlled trial of term neonates without complications was conducted in two obstetrical units in Argentina. Neonates were assigned to one of three groups: cord clamping at <15 sec (group 1), at 1 minute (group 2) or 3 minutes (group 3) and compared the venous hematocrit was measured 6 hours following birth. The hematocrits were 53.5% (group 1), 57.0% (group 2), and 59.4% (group 3). The prevalence of neonates with anemia, defined as hematocrits < 45% was low in the delayed cord clamping groups 2 and 3 (1.1 % and 0.0 % respectively) compared to 8.9% in the early cord clamping group. Importantly, the prevalence of polycythemia (hematocrit > 65%) was 4.4% in group 1 and 5.9% in group 2; but significantly increased in group 3, to 14.1%. No untoward effects due to these higher hematocrits were manifest. No increase in bilirubin levels or other deleterious clinical outcomes were evident in the delayed clamping groups, but in the early clamping group, prevalence of anemia was increased at 6, 24, and 48 hours. Maternal effects were also evaluated: blood loss at delivery and hematocrit differences between delivery and at 24 hours were similar amongst the three groups 3.

High neonatal hematocrits decrease over the first days of life

In a randomized, controlled study, the authors found that the number of polycythemic neonates with hematocrits > 65% dropped from 14.1% to 7.8% at 24-48 hours in the group that had 3 minutes of delay to cord clamping, who began with a mean of 59.4% hematocrit at 6 hours after birth3.

Ideal time for cord clamping is yet to be determined

Clinical studies have not established the optimum evidence-based time for cord clamping.

Neonatal specimen issues are directly relevant to the clinical laboratory

The current and growing trend towards longer delays in cord clamping after delivery will, based on the published literature, lead to greater numbers of polycythemic newborns and consequent laboratory samples with higher hematocrits.

We can expect the following (see below):

  • High hematocrit samples leave less sample after centrifugation for analysis (chemistries), and may lead to more quantity not sufficient (QNS) samples
  • High hematocrit samples clot more readily and may lead to rejected samples
  • High hematocrit samples are more viscous and may have more frequent clots in instrumentation


  1. Madan AS, Kumar R, Adams MM, Benitz WE, Geaghan SM, Widness JA. Reduction in Red Blood Cell Transfusions Using a Bedside Analyzer in Extremely Low Birth Weight Infants. J Perinatol 2005; 25: 21–25. doi:10.1038/
  2. Timing of umbilical cord clamping after birth. Committee Opinion No. 543. American College of Obstetricians and Gynecologists. Obstet Gynecol 2012; 120:1522–6.
  3. Cernadas JM, Carroli G, Pellegrini L, Otano L, Ferreira M, Ricci C, Casa O, Giordanob D, Lardizabal J. The Effect of Timing of Cord Clamping on Neonatal Venous Hematocrit Values and Clinical Outcome at Term: A Randomized, Controlled Trial. Pediatrics 2006; 117; e779; originally published online March 27, 2006; DOI: 10.1542/peds.2005-1156