Early Cord Clamping and Its Effect on some Hematological Determinants of Blood Viscosity in Neonates


Thirty full term newborns delivered normally through vagina were selected. Umbilical cord clamping was performed within 15 seconds in 15 newborns and after 3 minutes of delivery in the other 15 newborns. Blood samples were taken from placenta at zero time and from neonates at zero, 2 hours, 24 hours and 5 days after delivery.


To study the effects of early and late cord clamping on neonatal blood viscosity.

Setting: Al-Hussein University Hospital

Subjects and Methods
Thirty full term newborns delivered normally through vagina were selected. Umbilical cord clamping was performed within 15 seconds in 15 newborns and after 3 minutes of delivery in the other 15 newborns. Blood samples were taken from placenta at zero time and from neonates at zero, 2 hours, 24 hours and 5 days after delivery. Blood samples were tested for CBC, Differential blood count, C-reactive protein (CRP), bilirubin, hematocrit, total plasma protein, plasma fibrinogen, IgG, plasma albumin, HbF, RBCs aggregation, RBC deformity, blood and plasma viscosity,. Fetal blood volume of placenta was also determined. The results were compared with 10 healthy infants (10 months age).

Late cord clamping results in a moderate rise of blood viscosity mainly due to marked increase of hematocrit. The increased whole blood viscosity is the result of rise in plasma viscosity and RBCs aggregation, together with the lowered red cell deformity.

The moderate rise in blood viscosity in neonates with late cord clamping was not associated with clinical symptoms of impaired organ perfusion. 



Polycythemia defined as a hematocrit over 0.65, affects 2-6% of all newborn infants (15,24). Neonatal polycythemia may be associated with a high incidence of developmental and neurological abnormalities at one to seven years of age (3). Shohat and Ramamurthy (16,21) demonstrated a marked increase in the hematocrit and blood viscosity during the first hours of postnatal life and suggested that the time of blood sampling should be considered in the diagnosis of polycythemia and hyperviscosity. Blood groups found good correlation between cord hematocrit levels and peripheral venous hematocrit levels by age 2 h. thereby, suggesting the use of cord blood hematocrits for screening of neonatal Polycythemia (16).

Several previous studies have been addressed the effect of placental transfusion on the development of neonatal Polycythemia(4,23). Blood transfusion from the placenta to the neonate occurs when the umbilical cord is clamped at sometime after 5 seconds of birth. Before birth the fetus contains a blood volume of approximately 70ml/kg. Another 45 ml of blood per kg of fetal weight contained in the placenta (9). If umbilical cord is clamped 3 min after birth or later, or if the newborn is kept below the placenta before cord clamping, 35 ml/kg may flow into the neonate.

The rapid 50% increase in blood volume as a result of late cord clamping is counteracted by extravasation of plasma, so that the hematocrit rises from approximately 0.50 1/1 at birth to 0.65 1/1 at 2-4 hours of postnatal age (4,13,18,23). This increase in hematocrit may be associated with a 50% rise in blood viscosity (8). Blood viscosity is mainly determined by hematocrit, however, increased plasma viscosity, strong red cell aggregation and decreased red blood cell deformity may also contribute to an increase in blood viscosity (19).

Both plasma viscosity (10) and RBC aggregation (11) increase with increasing plasma fibrinogen concentration. Since high molecular weight proteins such as fibrinogen leave the vascular space slower than smaller proteins (e.g albumin) during extravasation of plasma (170, plasma viscosity and RBC aggregation could increase after late cord clamping. Moreover, the arterial pH may be affected by the time of cord clamping (6,14), thereby changing RBC deformability (2).

Neither blood viscosity nor determinants of blood viscosity have been reported for newborn infants with different modes of cord clamping.

The present study was designed to evaluate the effect of early and late cord clamping on postnatal changes in blood viscosity and its determinants (hematocrit, plasma viscosity, RBC aggregation and RBC deformability).

Study Methods
Neonates and blood Samples

Thirty healthy full-term vaginally born neonates were studied. The umbilical artery pH was 7.25, the 1-min Apgar score was 9 and the 2- and 5-min Apgar scores were 10 in all cases. The infants had gestational ages of 39 to 40 weeks and birth weights of 3.390 to 3.620g. All had birth weight appropriate for gestational age.

In 15 infants the umbilical cord was clamped within 10 seconds of birth (early cord clamping). Fifteen infants were kept at the level of the introitus vagina and the cords were clamped exactly 3 min after birth (late cord clamping). Clinical manifestations of hyperviscosity (15) were recorded each time when the infants were seen for blood sampling.

Blood (10ml) was collected from the placenta into EDTA (mg/ml) immediately after cord clamping before delivery of placenta.

Antecubital blood (2ml) was collected at 2h, 24h, and 5 days of age. Excessive squeezing and prolonged tourniquet application was avoided (21). The blood samples were used for routine laboratory CBC; 2h hematocrit; 24h hematocrit; leukocyte count; differential blood picture; CRP; bilirubin in jaundiced infants, 5days: bilirubin-screening test. Further bilirubin measurements were done at any age if the infant appeared jaundiced.

Infant blood samples were collected from 10 healthy infants at the age of 10± 2 months via venipuncture into EDTA tubes.

General Hematological Methods

Hematocrit was measured in duplicate by the microhematocrit method. The values were corrected for 2% of trapped plasma (8). RBC count, hemoglobin concentration and white cell count were determined using a coulter counter (coulter Electronics Inc. Harpenden, Herts, UK). Differential blood count was performed after Gimsa stain for staining blood smear. Reticulocytes were counted after the staining of a blood smear with brilliant crestyl blue. Hemoglobin F was quantified by the alkali denaturation test1).

Total plasma protein concentration was measured by Biuret test. Plasma Fibrinogen immunoglobulin G and albumin concentration were determined via radial-immunodiffusion Techniques (M partgin Kits, Behring, Murburg, Germany)

Hemorheological Methods

Al hemorheological measurements were carried out within 4 of blood collection (8). Blood and plasma viscosity was determined by means of a capillary viscometer that has been described in detail elsewhere (22). A tube with a diameter of 100 um and length of 1 cm was perfused with whole blood and plasma at a temperature of 37C and a pressure of 25 cmH2O. Viscosity (whole blood, and plasma) were calculated from the passage of the samples (total blood and plasma) and distilled water (T H2O) and from the viscosity of water at 37C(0.6915mpa.second). Volume of blood and plasma=Total blood and plasma/T H2O (0.6915).

Relative viscosity is calculated as ratio of blood to plasma viscosity.

RBCs aggregation (11,20) was assessed at 22C using the Myrenne Erythrocyte Aggregometer MA2 (Myrenne, Roetgen, Germany), which consists of Transparent cone plate viscometer. A blood sample with an adjusted hematocrit of 0.40 1/1 is heard for 20 second to disperse at RBC aggregates. The drive motor is then stopped and the light transmission increases with the time at a rate proportional to the rate of RBC aggregation. The increase in transmission of infra red light during 10s of blood stasis is recorded, integrated by a microprocessor and expressed as a percentage of the maximum possible light transmission (i.e. light transmission during 10 seconds without a sample). The deformability of single RBC was observed and measured at 22 using a counter-rotating, cone-plate rheoscope (19) (Effenberger, Munich, Germany), which was mounted on an inverted microscope (leitz Diaverts, Wetzlar, Germany; details of the method have been described elsewhere (12). Six shear stresses from 0.6 to 8.5 pa were applied and microphotographs of the cells were taken at each of the shear stresses. Deformation results in elongation of the RBC and deformation (D) is defined as D= (L-W)/ (L+W), where L is the length and W the width of the deformed cell.

Fetal Blood Volume of the Placenta

Fetal blood volume of the placenta i.e. the residual placental blood volume in placenta after umbilical cord clamping was determined by measurement of the HBF content (1) of the homogenized placenta, maternal and cord blood (5,7). Fetal blood volume of the placenta was calculated as ratio of HbF (gm) in placental homogenate divided by the HbF concentration (ml) in cord blood. The volume of cord blood removed before homogenization of the placenta was added to the fetal blood volume of placenta.

Since the total fetal placental blood volume is approximately 115ml/kg of neonatal body weight (9), neonatal blood volume was estimated as the difference between 115ml/kg and the fetal blood volume of the placenta.

Statistical Analysis

Analysis of variance for paired observations was used to test for changes in the measured parameters during the first five days after birth. The two neonatal groups (early vs late cord clamping) and the one old infants were compared using analysis of variance for unpaired observations.


The fetal blood volume of the placenta was 47±7ml/kg of neonatal weight in the early cord clamping group and 15± 4ml/kg in the late cord-clamping group.

Neonatal blood volume at birth calculated as the difference between an assumed total fetoplacental blood volume of 115ml/kg and the measured fetal blood volume of the placenta was 50% higher in the late cord clamping group then that of the early cord clamping group.

Hematocrit, hemoglobin F, plasma proteins and rheological parameters in cord blood were similar in both groups (tables 1,2). The hematocrit rose markedly in the late cord-clamping group during the first 2 hours after birth, but changed little during the following five days. At 2h of age the hematocrit ranged from 0.44 to 0.53 1/1 in infants with early cord clamping and from 0.58 to 0.70 1/1 in infants with late cord clamping. In the early cord clamping group the hematocrit decreased significantly after 24h (table 1).

At 24h of age, the hematocrit ranged from 0.37 to 0.48 1/1 in the infants with early cord clamping and from 0.54 to 0.67 1/1 in the infants with late cord clamping.

There was clinical manifestation of Polycythemia (i.e. central nervous, cardiopulmonary, gastrointestinal or renal) in both groups (15).

Bilirubin concentrations exceeded 15mg/dl in 3 of the 15 infants with late cord clamping and in none of the infants with early cord clamping.

Total plasma protein, albumin and fibrinogen concentrations increased significantly in both groups on day 5 (table 1). HbF did not differ among the two groups.

In both groups, changes in plasma viscosity and RBC aggregation followed the plasma protein concentrations. On day 5 plasma viscosity and RBC aggregation values were significantly higher than in cord blood (table 2). The increase in plasma viscosity and RBC aggregation were similar in both groups. RBC deformation was not affected by the timing of cord clamping and did not change during the first five days (table 2). Whole blood and relative viscosity in the infants with late cord clamping increased together with the hematocrit during the first 2 hours but did not change significantly during the following five days (tables 1 and 2).

At 2 to 120 hours of postnatal age, the hematocrit, blood viscosity and relative viscosity were significantly increased in the infants with late cord clamping.

Compared to old infants, the total plasma protein, albumin and fibrinogen concentration were significantly lower (p<0.05) in the neonates during the first 120h of postnatal life. Blood viscosity was significantly lower in infants with early cord clamping than in older infants (p<0.05) whereas in infants with late cord clamping blood viscosity was significantly increased at postnatal ages of 2 and 120hours (p<0.05)


Our study confirms previous reports on the effect of early and late cord clamping on fetal blood volume of the placenta (4,23). Assuming that the fetal blood volume of the placenta after early cord clamping represents the prenatal fetal blood volume in the placenta, cord clamping after 3 minutes of birth resulted in placental transfusion of about 35 ml/kg of birth weight. The acute volume expansion was counteracted by extravasation of plasma. The resulting increase in hematocrit from 0.50 to 0.63 1/1 in the infants with late cord clamping increased blood volume concentration of about 20-30 ml/kg (13).

Cord blood hematocrit was not affected by placental transfusion. This agrees with previous studies (4,18,25) and shows that cord blood hematocrit values do not predict Polycythemia resulting from placental transfusion.

In early cord clamping, neonatal plasma volume and hematocrit have been found constant during the first four hours (4,13,18,23). However, 24 hours after early cord clamping, hematocrit tends to decrease and plasma volume increases by about 10ml/kg (4,18). Our results agree with these previous studies. In contrast to these results, a recent study on infants whose cords were clamped at 10s of birth, showed an increase in the hematocrit by about 0.07 1/1 during the first 2 hours of life (21).

A marked rise in hematocrit in spite of early cord clamping may be explained by intrauterine placental transfusion (110. Hemoconcentration in the infants with late cord clamping was not associated with a rise in plasma protein concentrations during the first 24h(table 1). Ingomar et al (4) demonstrated that the transcapillary escape rate of albumin increases parallel to the placental transfusion. Our results suggest that the disappearance rate of high molecular weight proteins (e.g. fibrinogen) also increases parallel to the magnitude of placental transfusion, thereby keeping the constant. However, total plasma protein, albumin and fibrinogen concentration increased significantly after five days. The rise may be due to increased protein synthesis in the liver or by contraction of the extravascular space.

Plasma viscosity depends on the total plasma protein concentration but is more influenced by high molecular weight proteins i.e. fibrinogen, than by small proteins i.e. albumin (10). The increase in plasma viscosity (table2) on day 5 can be referred to the concomitant increase in total plasma proteins and plasma fibrinogen (table 1).

Increased RBC aggregation on day 5 can, therefore, be attributed to the rise in fibrinogen. RBC deformation was not affected by the mode of cord clamping and did not changes postnatally. In contrast to this finding, Linder Kamp et al.(12) observed a postnatal increase in RBCs filterability which they attributed to the rise in plasma fibrinogen and to changes in the RBC membrane lipid composition. RBC deformability as determined in the rheoscope is not influenced by plasma proteins.

We have not studied any biochemical properties of the RBC membrane in the present study.

Whole blood viscosity increase with rising hematocrit, increasing plasma viscosity, increasing RBCs aggregation and with decreasing RBCs deformability.

We concluded that 50% increase of blood viscosity was due to rising hematocrit. The subsequent increase in plasma viscosity did not raise the blood viscosity because of slight decrease in hematocrit (table 1).

RBCs aggregation increases blood viscosity only at low shear rates. RBCs aggregation, therefore, did not affect blood viscosity measured with our tube viscometer (22). However, the increase in plasma fibrinogen from 2.4g/l to 3.0g/l in the infants with late cord clamping (table 2) may have raised the blood viscosity by 20% at slow shear rate (10). Under physiological conditions RBC aggregation takes place only in veins, where shear forces are low. Strong RBC aggregation may impair venous return.

We concluded that late cord clamping results in a moderate rise of blood viscosity due to Hemoconcentration. The increase in blood viscosity was mainly caused by the rising hematocrit, but the rise in plasma viscosity and RBCs aggregation during the first postnatal days may have contributed to increased blood viscosity.

However, compared to older infants, blood viscosity in the neonates with late cord clamping was only moderately higher although the hematocrit was markedly elevated in these infants (table 2). This may be explained by the lower plasma viscosity (table 2) and the more pronounced viscosity reduction of neonatal RBC in narrow tubes (22). The moderate rise in blood viscosity may also explain why infants with late cord clamping did not develop clinical symptoms of impaired organ perfusion.

Table 1

Hematocrit, Plasma proteins, albumin and fibrinogen in the 3 studied groups 


total plasma









0.48± 0.04

5.5± 0.5

3.5 ±0.4

251± 48


0.47± 0.05

5.7± 0.6

3.5 ±0.4



0.43± 0.06

5.5± 0.6

3.6± 0.5

284± 66


0.44± 0.05

6.3 ±0.7

3.9± 0.4

310 ±71







0.50± 0.04

5.4± 0.7

3.4± 0.4

239± 54


0.63 ±0.05

5.7± 0.8

3.6± 0.5

266± 52


0.59± 0.05

5.6± 0.6

3.6± 0.4

248 ±33


0.59± 0.05

6± 0.8

3.8± 0.5

390± 51


0.47 ±0.05

7.3± 0.8

4.4± 0.8

344 ±62

[1]=Early cord clamping infants
[2]=Late cord clamping infants
[3]= Infants at 10± 2 months

Table 2

Plasma viscosity, Erythrocyte aggregation, RBCs Deformability, Whole blood viscosity and Relative viscosity in the 3 studied groups





blood viscosity





1.04± 0.08

3.9± 0.8

0.42± 0.05

2.9± 0.3



1.06± 0.1

4.1± 1.2

0.43± 0.05

2.8± 0.4

2.7± 0.3


1.07± 0.07

4.2± 1.4

0.4 0±.04

2.8± 0.4

2.5 ±0.5


1.18± 0.13

4.8± 1.5

0.3± 0.05

3.1± 0.4

2.6± 0.4




1.05± 0.06





























[1]=early cord clamping
[2]=Late cord clamping
[3] Infants at 10±2 months 



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Citation: published June 1999 on OBGYN.net


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