title: Whole-blood viscosity in the neonate: effects of gestational age, hematocrit, mean corpuscular volume and umbilical cord milking.
abstract: OBJECTIVE
  The American College of Obstetrics and Gynecology Committee on Obstetric Practice recently endorsed delayed cord clamping at preterm delivery. However, the committee report expressed the concern by some practitioners that delayed clamping or cord milking might induce hyperviscosity in preterm neonates. To address this issue we: (1) established reference ranges for whole-blood viscosity among preterm neonates (viscosity reference ranges had previously been reported only in term neonates) and (2) determined the effect of umbilical cord milking at deliveries <32 weeks gestation on subsequent blood viscosity measurements.
  
  
  METHODS
  This was a prospective study in two Neonatal Intensive Care Units. Blood viscosity was measured using a cone and plate viscometer. Associations were sought with gestation, hematocrit/hemoglobin and mean corpuscular volume. Reference ranges were determined for preterm infants <32 weeks gestation. Then, after umbilical cord milking at deliveries <32 weeks, viscosity was measured at birth and again during the 12 h after birth. In neonates with viscosities >95th % range, we sought signs of hyperviscosity (plethora, hypotonia, hypoglycemia, hyperbilirubinemia, thrombocytopenia).
  
  
  RESULTS
  Viscosity at higher and lower sheer rates were linearly related (n=32, r=0.971). Within the range of hematocrits measured (29-63%) viscosity correlated with hematocrit (r=0.877) and hemoglobin (r=0.853) but not with erythrocyte size (r=0.179). Viscosity was related to gestational age (n=58), primarily due to the lower hematocrits at lower gestational ages. In the 12 h after cord milking viscosity ranged from 3.1 to 9.5 centipoise. Three of twenty preterm, neonates had viscosities >95th % reference range. However, all values were well below those where hyperviscosity is defined in term neonates and all lacked features of hyperviscosity.
  
  
  CONCLUSIONS
  Cord blood viscosity is directly proportional to hematocrit/hemoglobin, lower at early gestation and not associated with erythrocyte size. Cord milking at preterm delivery is associated with a low risk of clinical hyperviscosity. Practioners should not refrain from cord milking at preterm delivery because of a concern that it will commonly cause neonatal hyperviscosity.
authors.affiliation: 1] Department of Women and Newborns, Intermountain Healthcare, Salt Lake City, UT, USA [2] Department of Women and Newborns, Neonatal Intensive Care Units, McKay-Dee Hospital Center, Ogden, UT, USA.
authors.forename: R D
authors.initials: RD
authors.lastname: Christensen
authors.affiliation: 1] Department of Women and Newborns, Intermountain Healthcare, Salt Lake City, UT, USA [2] Department of Women and Newborns, Neonatal Intensive Care Units, McKay-Dee Hospital Center, Ogden, UT, USA.
authors.forename: V L
authors.initials: VL
authors.lastname: Baer
authors.affiliation: 1] Department of Women and Newborns, Intermountain Healthcare, Salt Lake City, UT, USA [2] Department of Women and Newborns, Utah Valley Regional Medical Center, Provo, UT, USA.
authors.forename: E
authors.initials: E
authors.lastname: Gerday
authors.affiliation: 1] Department of Women and Newborns, Intermountain Healthcare, Salt Lake City, UT, USA [2] Department of Women and Newborns, Neonatal Intensive Care Units, McKay-Dee Hospital Center, Ogden, UT, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Sheffield
authors.affiliation: 1] Department of Women and Newborns, Intermountain Healthcare, Salt Lake City, UT, USA [2] Division of Maternal/Fetal Medicine, Department of Obstetrics and Gynecology, University of Utah School of Medicine, Salt Lake City, UT, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: Richards
authors.affiliation: Department of Women and Newborns, Utah Valley Regional Medical Center, Provo, UT, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Shepherd
authors.affiliation: Department of Research, Statistical Data Center, LDS Hospital, Salt Lake City, UT, USA.
authors.forename: G L
authors.initials: GL
authors.lastname: Snow
authors.affiliation: Department of Pathology, Intermountain Medical Center, Murray, UT, USA.
authors.forename: S T
authors.initials: ST
authors.lastname: Bennett
authors.affiliation: Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, USA.
authors.forename: E L
authors.initials: EL
authors.lastname: Frank
authors.affiliation: Department of Pediatrics, Brown Medical School, Women and Infant's Hospital of Rhode Island, Providence, RI, USA.
authors.forename: W
authors.initials: W
authors.lastname: Oh
mesh_terms: D001809:Blood Viscosity; D004909:Erythrocyte Indices; D005312:Fetal Blood / Q000502:physiology*; D005865:Gestational Age; D006400:Hematocrit; D006801:Humans; D007224:Infant Care; D007231:Infant, Newborn / Q000097:blood*; D007234:Infant, Premature / Q000097:blood; D016014:Linear Models; D011446:Prospective Studies; D014470:Umbilical Cord
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