Nucleated Red Blood Cells in Preterm Infants With Retinopathy of Prematurity
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《小儿科》
Neonatology Department of Pediatrics Department of Ophthalmology, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel
Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
ABSTRACT
Objective. The aim of this retrospective study was to examine hematologic indices of potential intrauterine hypoxia, including circulating nucleated red blood cells, lymphocytes, and platelets in preterm infants who developed retinopathy of prematurity (ROP) compared with suitable controls. We hypothesized that higher neonatal absolute nucleated red blood cell (ANRBC) and lymphocyte counts and lower platelets would be found in infants who developed ROP, compared with control infants.
Methods. Each of 23 infants with ROP was pair matched for gestational age and Apgar scores with a control without ROP. Criteria for exclusion in both groups included factors that may influence the ANRBCs at birth. Venous ANRBC counts were obtained within 1 hour of life. Statistical analyses used paired t tests, a paired Wilcoxon test, and backward stepwise-regression analysis.
Results. Groups did not differ in birth weight, gestational age, Apgar scores, or hematocrit, white blood cell, or platelets counts. The ANRBC counts at birth were significantly higher in infants who developed ROP than in controls.
Conclusions. Infants who develop ROP have higher ANRBC counts at birth than matched controls. We suggest that increased fetal erythropoiesis exists in preterm infants who later on will develop ROP. If correct, our interpretation supports the theory that long-lasting fetal hypoxia and/or ischemia may play a role in the pathogenesis of ROP.
Key Words: retinopathy of prematurity fetal hypoxia
Abbreviations: ROP, retinopathy of prematurity RBC, red blood cell WBC, white blood cell ANRBC, absolute nucleated red blood cell IVH, intraventricular hemorrhage
Retinopathy of prematurity (ROP) is a developmental vascular disorder that occurs in the incompletely vascularized retina of premature infants; it is a major cause of blindness in children in the developed and developing world. Progress in neonatal intensive care has led to an increased survival of small preterm infants and, subsequently, to an increasing incidence of ROP.1,2 In a population-based cohort study, Chiang et al3 reported that the overall incidence of ROP among newborn infants in New York State during the study period was 0.2%. Although many theories exist about the pathogenesis of ROP, the mechanisms by which preterm infants develop ROP are still unclear, and the cause of ROP is widely considered to be multifactorial.4–6 Hypoxia of retinal cells, secondary to any one of a variety of noxious perinatal events, is one of the possible culprits.5 In support of an ischemic-hypoxic theory are the facts that an increased rate of severe ROP has been found in infants suffering from fetal growth restriction7 and neonatal asphyxia,8 conditions known to potentially compromise blood flow and/or oxygen supply.
One of the well-described consequences of intrauterine hypoxia is increased compensatory erythropoiesis caused by increased erythropoietin secretion.9–11 In situations associated with intrauterine hypoxia, such as intrauterine growth restriction, maternal pregnancy-induced hypertension, or maternal diabetes or smoking, there is an elevation of nucleated red blood cell (RBC) counts at birth, presumably caused by increased compensatory erythropoiesis.9,12
The aim of this study was to examine hematologic indices of potential intrauterine hypoxia, including circulating nucleated RBCs, lymphocytes, and platelets in preterm infants who developed ROP compared with suitable controls. We hypothesized that higher neonatal absolute nucleated RBC (ANRBC) and lymphocyte counts and lower platelets would be found in infants who developed ROP, compared with control infants.
PATIENTS AND METHODS
Patients
We retrospectively analyzed the charts of all infants who were admitted to our NICUs, born at the Lis Maternity Hospital, Tel Aviv Sourasky Medical Center between January 1, 2002, and December 31, 2004, and who were diagnosed with ROP. During that period a strict protocol of ROP screening, which was consistent with the 1997 American Academy of Pediatrics guidelines,13,14 was followed. Briefly, all infants who were born with a birth weight of 1500 g or a gestational age of 28 weeks and sick infants (sick enough to require supplemental oxygen therapy, mechanical ventilation, or continuous positive airway pressure or blood pressure support) of >1500 g in birth weight underwent a dilated indirect ophthalmoscopic examination to detect ROP. The examination was conducted in all infants by a single experienced pediatric ophthalmologist (C.S.). The examination was performed in all infants between 4 and 6 weeks' chronological age or between 31 and 33 weeks' postmenstrual age.14 Scheduling of follow-up examinations was determined by the findings at the first examination, using the International Classification of Retinopathy of Prematurity.13,14 Follow-up examination was continued until vascularization had proceeded to zone 3. Infants with threshold disease were considered candidates for ablative surgery of at least 1 eye within 72 hours of diagnosis.
Each infant with ROP of any stage was pair matched with the infant admitted immediately after him or her who did not develop ROP and had the same gestational age (±1 week) and 1- and 5- minute Apgar scores (±1). In an attempt to control for the various variables known to affect neonatal nucleated RBC counts, we excluded from the study infants in both groups who were born to women with gestational or insulin-dependent diabetes15; pregnancy-induced hypertension16; intrauterine growth retardation (defined as a birth weight below the 10th percentile using the Lubechenco curves12,17); placental abruption or placenta previa18; any maternal heart, kidney, lung, or other chronic condition; drug, tobacco, or alcohol abuse19; perinatal infections (eg, maternal fever, maternal leukocytosis [white blood cells (WBCs) > 15.0 x 103/mm3], clinical signs of chorioamnionitis such as fever and abdominal tenderness)20; any abnormality in electronic intrapartum monitoring18; or infants with low Apgar scores (<6 at 1 or 5 minutes).21 We also excluded infants with perinatal blood loss, hemolysis (blood-group incompatibility with positive Coombs test or hematocrit of <45%),22 or chromosomal anomalies.23 Because of these exclusion criteria, we had to exclude 10 potential controls who were each replaced by the appropriate control infant born immediately after it. Follow-up data were available from the medical charts in our pediatric ophthalmology clinic, when available, or by telephone interview with the parents.
Hematologic Methods
In our institution, all preterm infants admitted to the NICU undergo a routine complete blood count with differential count within the first hour of life. Venous blood samples for complete blood cell counts were analyzed according to laboratory routine using an STK-S counter (Coulter Corporation, Hialeah, FL). Differential cell counts were performed manually, and nucleated RBC counts were counted per 100 WBCs. We showed previously that leukocyte counts and ANRBC numbers are not independent.24 Thus, traditional expression of nucleated RBCs as their number per 100 WBCs might introduce a significant bias. Therefore, we expressed the number of nucleated RBCs as ANRBCs rather than per 100 leukocytes, and the WBC count was expressed as corrected for the presence of nucleated RBCs. We also corrected the absolute lymphocyte count, another potential index of fetal hypoxia.25
Statistical Methods
Data are reported as mean ± SD, n (%), or, for non-normally distributed variables (such as ANRBCs or Apgar scores) as median (range). Statistical analysis included the 2-tailed paired t test for normally distributed variables and paired Wilcoxon test for ANRBCs or Apgar scores. Backward stepwise-regression analysis was used to assess the effect of gestational age (or birth weight), 1- or 5- minute Apgar scores, intraventricular hemorrhage (IVH) status, and ANRBC count (independent variables) on the ROP status (dependent variable). We also used Pearson ranked-regression analysis to study the correlation between ROP severity (defined by its stage from 0 [no ROP] to 4, whichever the zone) and the ANRBC count. P < .05 was considered significant.
Our local institutional review board approved the study. Because all preterm patients in our institution receive a routine complete blood count after birth, including nucleated RBC count, the requirement for informed consent was waived.
RESULTS
A total of 23 infants with ROP were retained for analysis and compared with 23 controls. Four additional infants with ROP were excluded because of maternal diabetes (n = 2), neonatal polycythemia (n = 1), and maternal asthma (n = 1). Table 1 depicts some major demographic and clinical characteristics of infants with ROP and controls. There were no significant differences between groups in all clinical or demographic parameters considered, to the inclusion of infant birth weight, gestational age, major diagnoses such as respiratory distress syndrome, patent ductus arteriosus, IVH, and periventricular leukomalacia, and major treatments and procedures such as umbilical artery and vein catheters, mechanical ventilation, antibiotic treatment, indomethacin for patent ductus arteriosus closure, and endotracheal administration of surfactant. By design, infants with ROP did not differ from controls in terms of gestational age and Apgar scores.
DISCUSSION
In a retrospective study, we found that the development of ROP was associated with an increase in ANRBCs. In our study we excluded small-for-gestational-age infants, which is an important confounding variable.26 We also excluded infants with other factors associated with potentially increased ANRBC counts, including hemolysis,22 chromosomal anomalies,23 maternal diabetes,15,27 and neurologic insults.28,29 It is important to note that the 2 groups in our study (infants with ROP and controls) ended up being very similar in birth weight, gestational age, Apgar scores (by design), and major neonatal complications. Thus, we believe that our study confirms our hypothesis that as a group, preterm infants with ROP have increased neonatal ANRBC counts.
The mechanism by which ROP is associated with increased circulating neonatal ANRBC counts is unknown. A likely explanation is relative fetal hypoxia.15,25,30 In favor of a contribution of hypoxia/ischemia in the pathogenesis of ROP are the facts that an increased rate of ROP has been found in conditions known to potentially compromise retinal blood flow and/or oxygen supply, such as fetal growth restriction7 and severe neonatal asphyxia.8 In our study, the lymphocyte count, also believed to be an indicator of fetal hypoxia,25 was not elevated, and the platelet count was not decreased, but these hematologic parameters might indicate acute rather than chronic hypoxia.25 In this retrospective study, cord blood gases, which theoretically might have helped in the diagnosis of fetal hypoxemia, were not routinely obtained in all infants. However, cord blood gases are indicative of the acute oxygenation status of the fetus in contrast with ANRBCs, which are indicative of the oxygenation status of the fetus at least a few days before delivery.31 In terms of timing, if the elevation of ANRBC counts in the ROP group is indeed related to fetal hypoxia, as we speculate, this hypoxia must have been of sufficient duration to stimulate erythropoietin secretion. The relationship between hypoxia and ROP is not yet completely investigated but might involve an increase in vascular endothelial growth factor production induced by hypoxia, which in turn may stimulate neovascularization.5,32,33 Another possibility under investigation is hypoxia-induced stimulation of insulin-like growth factor-binding protein-1 production, which in turn may decrease free insulin-like growth factor concentrations, which may prevent normal vessel growth.5,33–35
We suggest that increased fetal erythropoiesis exists in preterm infants who later on will develop ROP. If correct, our interpretation supports the theory that fetal hypoxia and/or ischemia may play a role in the pathogenesis of ROP. Although the retrospective aspect of our study requires a replication of results in a prospective manner, we speculate that elevated ANRBCs at birth may help to define a subgroup of preterm infants at increased risk for ROP.
FOOTNOTES
Accepted Jun 16, 2005.
No conflict of interest declared.
REFERENCES
Silverman WA. Retrolental Fibroplasia: A Modern Parable. New York, NY: Grune and Stratton; 1980
Kim TI, Sohn J, Pi SY, Yoon YH. Postnatal risk factors of retinopathy of prematurity. Paediatr Perinat Epidemiol. 2004;18 :130 –134
Chiang MF, Arons RR, Flynn JT, Starren JB. Incidence of retinopathy of prematurity from 1996 to 2000: analysis of a comprehensive New York state patient database. Ophthalmology. 2004;111 :1317 –1325
Campbell K. Intensive oxygen therapy as a possible cause of retrolental fibroplasia; a clinical approach. Med J Aust. 1951;2(2) :48 –50
Smith LE. Pathogenesis of retinopathy of prematurity. Semin Neonatol. 2003;8 :469 –473
Mccolm JR, Fleck BW. Retinopathy of prematurity: causation. Semin Neonatol. 2001;6 :453 –460
Arroe M, Peitersen B. Retinopathy of prematurity in a Danish neonatal intensive care unit, 1985–1991. Acta Ophthalmol Suppl. 1993;210 :37 –40
Finne PH. Erythropoietin levels in cord blood as an indicator of intrauterine hypoxia. Acta Paediatr Scand. 1966;55 :478 –489
Vatansever U, Acunas B, Demir M, et al. Nucleated red blood cell counts and erythropoietin levels in high-risk neonates. Pediatr Int. 2002;44 :590 –595
Ostlund E, Lindholm H, Hemsen A, Fried G. Fetal erythropoietin and endothelin-1: relation to hypoxia and intrauterine growth retardation. Acta Obstet Gynecol Scand. 2000;79 :276 –282
Minior VK, Bernstein PS, Divon MY. Nucleated red blood cells in growth-restricted fetuses: associations with short-term neonatal outcome. Fetal Diagn Ther. 2000;15 :165 –169
Fierson WM, Palmer EA, Biglan AW, Flynn JT, Petersen RA, Phelps DL. Screening examination of premature infants for retinopathy of prematurity. A joint statement of the American Academy of Pediatrics, the American Association for Pediatric Ophthalmology and Strabismus, and the American Academy of Ophthalmology. Pediatrics. 1997;100 :273
American Academy of Pediatrics, Section on Ophthalmology. Screening examination of premature infants for retinopathy of prematurity. Pediatrics. 2001;108 :809 –811
Green DW, Mimouni F. Nucleated erythrocytes in healthy infants and in infants of diabetic mothers. J Pediatr. 1990;116 :129 –131
Sinha HB, Mukherjee AK, Bala D. Cord blood haemoglobin (including foetal haemoglobin), and nucleated red cells in normal and toxaemic pregnancies. Indian Pediatr. 1972;9 :5490 –5493
Lubchenco LO, Hansman C, Dressler M, Boyd E. Intrauterine growth as estimated from live-born birth weight data at 24 to 42 weeks gestation. Pediatrics. 1963;32 :793 –799
Korst LM, Phelan JP, Ahn MO, Martin GI. Nucleated red blood cells: an update on the marker for fetal asphyxia. Am J Obstet Gynecol. 1996;175 :843 –846
Halmesmaki E, Teramo KA, Widness JA, Clemons GK, Ylikorkala O. Maternal alcohol abuse is associated with elevated fetal erythropoietin levels. Obstet Gynecol. 1990;76 :219 –222
Leikin E, Garry D, Visintainer P, Verma U, Tejani N. Correlation of neonatal nucleated red blood cell counts in preterm infants with histologic chorioamnionitis. Am J Obstet Gynecol. 1997;177 :27 –30
Hanlon-Lundberg KM, Kirby RS. Nucleated red blood cells as a marker of acidemia in term neonates. Am J Obstet Gynecol. 1999;181 :196 –201
Thomas RM, Canning CE, Cotes PM, et al. Erythropoietin and cord blood haemoglobin in the regulation of human fetal erythropoiesis. Br J Obstet Gynaecol. 1983;90 :795 –800
Oski FA, Naiman JL. Hematologic Problems in the Newborn. 2nd ed. Philadelphia, PA: WB Saunders Co; 1972:15 –17
Green DW, Khouri J, Mimouni FB. Neonatal hematocrit and maternal glycemic control in insulin-dependent diabetes. J Pediatr. 1992;120 :302 –305
Phelan JP, Korst LM, Ahn MO, Martin GI. Neonatal nucleated red blood cell and lymphocyte counts in fetal brain injury. Obstet Gynecol. 1998;91 :485 –489
Snijders RJM, Abbas A, Melby O, Ireland RM, Nicolaides KH. Fetal plasma erythropoietin concentration in severe growth retardation. Am J Obstet Gynecol. 1993;168 :615 –619
Mimouni F, Miodovnik M, Siddiqi TA, Butler JB, Holroyde J, Tsang RC. Neonatal polycythemia in infants of insulin-dependent diabetic mothers. Obstet Gynecol. 1986;68 :370 –372
Green DW, Hendon B, Mimouni F. Nucleated erythrocytes and intraventricular hemorrhage in preterm neonates. Pediatrics. 1995;96 :475 –478
Naeye RL, Localio R. Determining the time before birth when ischemia and hypoxemia initiated cerebral palsy. Obstet Gynecol. 1995;86 :713 –719
Hermansen MC. Nucleated red blood cells in the fetus and newborn. Arch Dis Child Fetal Neonatal Ed. 2001;84 :F211 –F215
Sheffer-Mimouni G, Mimouni FB, Lubetzky R, Kupferminc M, Deutsch V, Dollberg S. Labor does not affect the neonatal absolute nucleated red blood cell count. Am J Perinatol. 2003;20 :367 –371
Leske DA, Wu J, Fautsch MP, et al. The role of VEGF and IGF-1 in a hypercarbic oxygen-induced retinopathy rat model of ROP. Mol Vis. 2004;10 :43 –50
Smith LE. Pathogenesis of retinopathy of prematurity. Growth Horm IGF Res. 2004;14(suppl A) :S140 –S144
Kajimura S, Aida K, Duan C. Insulin-like growth factor-binding protein-1 (IGFBP-1) mediates hypoxia-induced embryonic growth and developmental retardation. Proc Natl Acad Sci USA. 2005;102 :1240 –1245
Ozen S, Akisu M, Baka M, et al. Insulin-like growth factor attenuates apoptosis and mucosal damage in hypoxia/reoxygenation-induced intestinal injury. Biol Neonate. 2004;87 :91 –96(Ronit Lubetzky, MD, Chaim)
Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
ABSTRACT
Objective. The aim of this retrospective study was to examine hematologic indices of potential intrauterine hypoxia, including circulating nucleated red blood cells, lymphocytes, and platelets in preterm infants who developed retinopathy of prematurity (ROP) compared with suitable controls. We hypothesized that higher neonatal absolute nucleated red blood cell (ANRBC) and lymphocyte counts and lower platelets would be found in infants who developed ROP, compared with control infants.
Methods. Each of 23 infants with ROP was pair matched for gestational age and Apgar scores with a control without ROP. Criteria for exclusion in both groups included factors that may influence the ANRBCs at birth. Venous ANRBC counts were obtained within 1 hour of life. Statistical analyses used paired t tests, a paired Wilcoxon test, and backward stepwise-regression analysis.
Results. Groups did not differ in birth weight, gestational age, Apgar scores, or hematocrit, white blood cell, or platelets counts. The ANRBC counts at birth were significantly higher in infants who developed ROP than in controls.
Conclusions. Infants who develop ROP have higher ANRBC counts at birth than matched controls. We suggest that increased fetal erythropoiesis exists in preterm infants who later on will develop ROP. If correct, our interpretation supports the theory that long-lasting fetal hypoxia and/or ischemia may play a role in the pathogenesis of ROP.
Key Words: retinopathy of prematurity fetal hypoxia
Abbreviations: ROP, retinopathy of prematurity RBC, red blood cell WBC, white blood cell ANRBC, absolute nucleated red blood cell IVH, intraventricular hemorrhage
Retinopathy of prematurity (ROP) is a developmental vascular disorder that occurs in the incompletely vascularized retina of premature infants; it is a major cause of blindness in children in the developed and developing world. Progress in neonatal intensive care has led to an increased survival of small preterm infants and, subsequently, to an increasing incidence of ROP.1,2 In a population-based cohort study, Chiang et al3 reported that the overall incidence of ROP among newborn infants in New York State during the study period was 0.2%. Although many theories exist about the pathogenesis of ROP, the mechanisms by which preterm infants develop ROP are still unclear, and the cause of ROP is widely considered to be multifactorial.4–6 Hypoxia of retinal cells, secondary to any one of a variety of noxious perinatal events, is one of the possible culprits.5 In support of an ischemic-hypoxic theory are the facts that an increased rate of severe ROP has been found in infants suffering from fetal growth restriction7 and neonatal asphyxia,8 conditions known to potentially compromise blood flow and/or oxygen supply.
One of the well-described consequences of intrauterine hypoxia is increased compensatory erythropoiesis caused by increased erythropoietin secretion.9–11 In situations associated with intrauterine hypoxia, such as intrauterine growth restriction, maternal pregnancy-induced hypertension, or maternal diabetes or smoking, there is an elevation of nucleated red blood cell (RBC) counts at birth, presumably caused by increased compensatory erythropoiesis.9,12
The aim of this study was to examine hematologic indices of potential intrauterine hypoxia, including circulating nucleated RBCs, lymphocytes, and platelets in preterm infants who developed ROP compared with suitable controls. We hypothesized that higher neonatal absolute nucleated RBC (ANRBC) and lymphocyte counts and lower platelets would be found in infants who developed ROP, compared with control infants.
PATIENTS AND METHODS
Patients
We retrospectively analyzed the charts of all infants who were admitted to our NICUs, born at the Lis Maternity Hospital, Tel Aviv Sourasky Medical Center between January 1, 2002, and December 31, 2004, and who were diagnosed with ROP. During that period a strict protocol of ROP screening, which was consistent with the 1997 American Academy of Pediatrics guidelines,13,14 was followed. Briefly, all infants who were born with a birth weight of 1500 g or a gestational age of 28 weeks and sick infants (sick enough to require supplemental oxygen therapy, mechanical ventilation, or continuous positive airway pressure or blood pressure support) of >1500 g in birth weight underwent a dilated indirect ophthalmoscopic examination to detect ROP. The examination was conducted in all infants by a single experienced pediatric ophthalmologist (C.S.). The examination was performed in all infants between 4 and 6 weeks' chronological age or between 31 and 33 weeks' postmenstrual age.14 Scheduling of follow-up examinations was determined by the findings at the first examination, using the International Classification of Retinopathy of Prematurity.13,14 Follow-up examination was continued until vascularization had proceeded to zone 3. Infants with threshold disease were considered candidates for ablative surgery of at least 1 eye within 72 hours of diagnosis.
Each infant with ROP of any stage was pair matched with the infant admitted immediately after him or her who did not develop ROP and had the same gestational age (±1 week) and 1- and 5- minute Apgar scores (±1). In an attempt to control for the various variables known to affect neonatal nucleated RBC counts, we excluded from the study infants in both groups who were born to women with gestational or insulin-dependent diabetes15; pregnancy-induced hypertension16; intrauterine growth retardation (defined as a birth weight below the 10th percentile using the Lubechenco curves12,17); placental abruption or placenta previa18; any maternal heart, kidney, lung, or other chronic condition; drug, tobacco, or alcohol abuse19; perinatal infections (eg, maternal fever, maternal leukocytosis [white blood cells (WBCs) > 15.0 x 103/mm3], clinical signs of chorioamnionitis such as fever and abdominal tenderness)20; any abnormality in electronic intrapartum monitoring18; or infants with low Apgar scores (<6 at 1 or 5 minutes).21 We also excluded infants with perinatal blood loss, hemolysis (blood-group incompatibility with positive Coombs test or hematocrit of <45%),22 or chromosomal anomalies.23 Because of these exclusion criteria, we had to exclude 10 potential controls who were each replaced by the appropriate control infant born immediately after it. Follow-up data were available from the medical charts in our pediatric ophthalmology clinic, when available, or by telephone interview with the parents.
Hematologic Methods
In our institution, all preterm infants admitted to the NICU undergo a routine complete blood count with differential count within the first hour of life. Venous blood samples for complete blood cell counts were analyzed according to laboratory routine using an STK-S counter (Coulter Corporation, Hialeah, FL). Differential cell counts were performed manually, and nucleated RBC counts were counted per 100 WBCs. We showed previously that leukocyte counts and ANRBC numbers are not independent.24 Thus, traditional expression of nucleated RBCs as their number per 100 WBCs might introduce a significant bias. Therefore, we expressed the number of nucleated RBCs as ANRBCs rather than per 100 leukocytes, and the WBC count was expressed as corrected for the presence of nucleated RBCs. We also corrected the absolute lymphocyte count, another potential index of fetal hypoxia.25
Statistical Methods
Data are reported as mean ± SD, n (%), or, for non-normally distributed variables (such as ANRBCs or Apgar scores) as median (range). Statistical analysis included the 2-tailed paired t test for normally distributed variables and paired Wilcoxon test for ANRBCs or Apgar scores. Backward stepwise-regression analysis was used to assess the effect of gestational age (or birth weight), 1- or 5- minute Apgar scores, intraventricular hemorrhage (IVH) status, and ANRBC count (independent variables) on the ROP status (dependent variable). We also used Pearson ranked-regression analysis to study the correlation between ROP severity (defined by its stage from 0 [no ROP] to 4, whichever the zone) and the ANRBC count. P < .05 was considered significant.
Our local institutional review board approved the study. Because all preterm patients in our institution receive a routine complete blood count after birth, including nucleated RBC count, the requirement for informed consent was waived.
RESULTS
A total of 23 infants with ROP were retained for analysis and compared with 23 controls. Four additional infants with ROP were excluded because of maternal diabetes (n = 2), neonatal polycythemia (n = 1), and maternal asthma (n = 1). Table 1 depicts some major demographic and clinical characteristics of infants with ROP and controls. There were no significant differences between groups in all clinical or demographic parameters considered, to the inclusion of infant birth weight, gestational age, major diagnoses such as respiratory distress syndrome, patent ductus arteriosus, IVH, and periventricular leukomalacia, and major treatments and procedures such as umbilical artery and vein catheters, mechanical ventilation, antibiotic treatment, indomethacin for patent ductus arteriosus closure, and endotracheal administration of surfactant. By design, infants with ROP did not differ from controls in terms of gestational age and Apgar scores.
DISCUSSION
In a retrospective study, we found that the development of ROP was associated with an increase in ANRBCs. In our study we excluded small-for-gestational-age infants, which is an important confounding variable.26 We also excluded infants with other factors associated with potentially increased ANRBC counts, including hemolysis,22 chromosomal anomalies,23 maternal diabetes,15,27 and neurologic insults.28,29 It is important to note that the 2 groups in our study (infants with ROP and controls) ended up being very similar in birth weight, gestational age, Apgar scores (by design), and major neonatal complications. Thus, we believe that our study confirms our hypothesis that as a group, preterm infants with ROP have increased neonatal ANRBC counts.
The mechanism by which ROP is associated with increased circulating neonatal ANRBC counts is unknown. A likely explanation is relative fetal hypoxia.15,25,30 In favor of a contribution of hypoxia/ischemia in the pathogenesis of ROP are the facts that an increased rate of ROP has been found in conditions known to potentially compromise retinal blood flow and/or oxygen supply, such as fetal growth restriction7 and severe neonatal asphyxia.8 In our study, the lymphocyte count, also believed to be an indicator of fetal hypoxia,25 was not elevated, and the platelet count was not decreased, but these hematologic parameters might indicate acute rather than chronic hypoxia.25 In this retrospective study, cord blood gases, which theoretically might have helped in the diagnosis of fetal hypoxemia, were not routinely obtained in all infants. However, cord blood gases are indicative of the acute oxygenation status of the fetus in contrast with ANRBCs, which are indicative of the oxygenation status of the fetus at least a few days before delivery.31 In terms of timing, if the elevation of ANRBC counts in the ROP group is indeed related to fetal hypoxia, as we speculate, this hypoxia must have been of sufficient duration to stimulate erythropoietin secretion. The relationship between hypoxia and ROP is not yet completely investigated but might involve an increase in vascular endothelial growth factor production induced by hypoxia, which in turn may stimulate neovascularization.5,32,33 Another possibility under investigation is hypoxia-induced stimulation of insulin-like growth factor-binding protein-1 production, which in turn may decrease free insulin-like growth factor concentrations, which may prevent normal vessel growth.5,33–35
We suggest that increased fetal erythropoiesis exists in preterm infants who later on will develop ROP. If correct, our interpretation supports the theory that fetal hypoxia and/or ischemia may play a role in the pathogenesis of ROP. Although the retrospective aspect of our study requires a replication of results in a prospective manner, we speculate that elevated ANRBCs at birth may help to define a subgroup of preterm infants at increased risk for ROP.
FOOTNOTES
Accepted Jun 16, 2005.
No conflict of interest declared.
REFERENCES
Silverman WA. Retrolental Fibroplasia: A Modern Parable. New York, NY: Grune and Stratton; 1980
Kim TI, Sohn J, Pi SY, Yoon YH. Postnatal risk factors of retinopathy of prematurity. Paediatr Perinat Epidemiol. 2004;18 :130 –134
Chiang MF, Arons RR, Flynn JT, Starren JB. Incidence of retinopathy of prematurity from 1996 to 2000: analysis of a comprehensive New York state patient database. Ophthalmology. 2004;111 :1317 –1325
Campbell K. Intensive oxygen therapy as a possible cause of retrolental fibroplasia; a clinical approach. Med J Aust. 1951;2(2) :48 –50
Smith LE. Pathogenesis of retinopathy of prematurity. Semin Neonatol. 2003;8 :469 –473
Mccolm JR, Fleck BW. Retinopathy of prematurity: causation. Semin Neonatol. 2001;6 :453 –460
Arroe M, Peitersen B. Retinopathy of prematurity in a Danish neonatal intensive care unit, 1985–1991. Acta Ophthalmol Suppl. 1993;210 :37 –40
Finne PH. Erythropoietin levels in cord blood as an indicator of intrauterine hypoxia. Acta Paediatr Scand. 1966;55 :478 –489
Vatansever U, Acunas B, Demir M, et al. Nucleated red blood cell counts and erythropoietin levels in high-risk neonates. Pediatr Int. 2002;44 :590 –595
Ostlund E, Lindholm H, Hemsen A, Fried G. Fetal erythropoietin and endothelin-1: relation to hypoxia and intrauterine growth retardation. Acta Obstet Gynecol Scand. 2000;79 :276 –282
Minior VK, Bernstein PS, Divon MY. Nucleated red blood cells in growth-restricted fetuses: associations with short-term neonatal outcome. Fetal Diagn Ther. 2000;15 :165 –169
Fierson WM, Palmer EA, Biglan AW, Flynn JT, Petersen RA, Phelps DL. Screening examination of premature infants for retinopathy of prematurity. A joint statement of the American Academy of Pediatrics, the American Association for Pediatric Ophthalmology and Strabismus, and the American Academy of Ophthalmology. Pediatrics. 1997;100 :273
American Academy of Pediatrics, Section on Ophthalmology. Screening examination of premature infants for retinopathy of prematurity. Pediatrics. 2001;108 :809 –811
Green DW, Mimouni F. Nucleated erythrocytes in healthy infants and in infants of diabetic mothers. J Pediatr. 1990;116 :129 –131
Sinha HB, Mukherjee AK, Bala D. Cord blood haemoglobin (including foetal haemoglobin), and nucleated red cells in normal and toxaemic pregnancies. Indian Pediatr. 1972;9 :5490 –5493
Lubchenco LO, Hansman C, Dressler M, Boyd E. Intrauterine growth as estimated from live-born birth weight data at 24 to 42 weeks gestation. Pediatrics. 1963;32 :793 –799
Korst LM, Phelan JP, Ahn MO, Martin GI. Nucleated red blood cells: an update on the marker for fetal asphyxia. Am J Obstet Gynecol. 1996;175 :843 –846
Halmesmaki E, Teramo KA, Widness JA, Clemons GK, Ylikorkala O. Maternal alcohol abuse is associated with elevated fetal erythropoietin levels. Obstet Gynecol. 1990;76 :219 –222
Leikin E, Garry D, Visintainer P, Verma U, Tejani N. Correlation of neonatal nucleated red blood cell counts in preterm infants with histologic chorioamnionitis. Am J Obstet Gynecol. 1997;177 :27 –30
Hanlon-Lundberg KM, Kirby RS. Nucleated red blood cells as a marker of acidemia in term neonates. Am J Obstet Gynecol. 1999;181 :196 –201
Thomas RM, Canning CE, Cotes PM, et al. Erythropoietin and cord blood haemoglobin in the regulation of human fetal erythropoiesis. Br J Obstet Gynaecol. 1983;90 :795 –800
Oski FA, Naiman JL. Hematologic Problems in the Newborn. 2nd ed. Philadelphia, PA: WB Saunders Co; 1972:15 –17
Green DW, Khouri J, Mimouni FB. Neonatal hematocrit and maternal glycemic control in insulin-dependent diabetes. J Pediatr. 1992;120 :302 –305
Phelan JP, Korst LM, Ahn MO, Martin GI. Neonatal nucleated red blood cell and lymphocyte counts in fetal brain injury. Obstet Gynecol. 1998;91 :485 –489
Snijders RJM, Abbas A, Melby O, Ireland RM, Nicolaides KH. Fetal plasma erythropoietin concentration in severe growth retardation. Am J Obstet Gynecol. 1993;168 :615 –619
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