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Risk factors and growth factors in ROP
Early Human Development 85 (2009) S79–S82
Contents lists available at ScienceDirect
Early Human Development j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / e a r l h u m d ev
Risk factors and growth factors in ROP C. Romagnoli Division of Neonatology, Catholic University of Rome, Largo A. Gemelli, 8 00168, Rome, Italy
a r t i c l e
i n f o
Keywords: Retinopathy of prematurity Vascular growth factors Blood transfusion Infection
a b s t r a c t Retinopathy of prematurity (ROP) is a multifactorial disease which incidence is increasing with increasing survival of very preterm infants. Pathogenic pathway is characterised by abnormal retinal vascular development modulated by vascular growth factors: low IGF-1 in the first phase and high VEGF in the second phase. Many causal factors are able to influence retinal vascularization: gestational age, birth weight, oxygen administration, perinatal bacterial or fungal infections, and blood transfusions. All risk factors, both oxygen and not-oxygen-regulated, have been studied considering the whole period from hospital birth to the hospital discharge, but it is possible that postnatal risk factors may be determinant in a time-dependent way. Analysis of factors involved in the pathogenesis of ROP suggests that their action begins long before anatomical clinical features become appreciable and this is strengthened by the essential role of risk factors from the first two to four weeks of life, thus preventive strategies in very preterm infants should be carried out since birth. © 2009 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Retinopathy of prematurity (ROP) is a multifactorial disease that affects premature infants and it remains a major cause of blindness and visual impairment despite of continuous improvements in neonatal care [1]. Data on the incidence of ROP in industrialized countries within the past decade are controversial and, although some studies show a decline in incidence and severity of the disease, recent reports show a greater occurrence of more severe ROP [2–5]. Pathogenic pathway is characterised by abnormal retinal vascular development modulated by vascular growth factors according to molecular model organised in two distinct phases: “Phase I” involving delayed retinal vascular growth after premature birth and “Phase II” concerning uncontrolled proliferative growth of retinal blood vessels [6,7]. Growth factors as well as biochemical mediators are involved in this complex pathogenic mechanism and also clinical risk factors are correlated with development of ROP. 2. Growth factors Recent research data suggest a significant role of vascular endothelial growth factor (VEGF) and of insulin-like growth factor 1 (IGF-1) in the pathogenesis of ROP [6,7]. VEGF is involved in retinal vascular development and it is expressed in response to hypoxia. In normal condition neural retina develops anterior to the vasculature and the subsequent localized hypoxia stimulates production of VEGF anterior to the developing vessels. After premature birth, in phase I of ROP the sudden postnatal increase of tissue oxygen tension
E-mail address: [email protected]. 0378-3782/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.earlhumdev.2009.08.026
(physiological or iatrogenic) suppresses the VEGF mRNA expression and the normal VEGF-driven vascular growth and it promotes apoptosis of vascular endothelial cells and vaso-obliteration [8,9]. However, in the phase I, development of normal neural retina occurs allowing non-vascularized retina to become hypoxic. At this time VEGF accumulation occurs anterior to the vasculature, but VEGF is not able to stimulate angiogenesis because of lack of IGF-1 that exerts a permissive role in VEGF-induced neovascularization. In other words the low levels of IGF-1 in phase I of ROP inhibit VEGF activity in order to prevent normal survival of vascular endothelial cells [10] and to inhibit normal retinal vascularization. This allows the neural retina to develop under hypoxic condition and to induce more VEGF production and accumulation. This overproduction of VEGF, at a determined postmenstrual age (30–31 weeks) when IGF-1 increases and reaches normal levels, induces an uncontrolled neovascularization that may lead to retinal detachment. In this phase of ROP the role of VEGF is verified also by reports on the positive effects of anti-VEGF drugs (Bevacizumab) in controlling neovascularization [11–15]. This complex mechanism is reported by many clinical and experimental observations. Firstly, it is well known that patients with genetic defects in the GH/IGF-1 axis show an abnormal retinal vascularization characterised by few vascular branching vessels [16]. Moreover, the retinal blood vessels grow more slowly in IGF-1-null mice than in those normal. Secondly, it has been demonstrated a direct relationship between serum levels of IGF-1 and developing ROP and severity. Preterm infants developing ROP showed lower serum IGF-1 levels as compared with infants without ROP, and the duration of low IGF-1 levels correlated strongly with the severity of ROP [5,17,18]. Finally, it has been demonstrated that IGF-1 is able to control maximum VEGF activation of the Akt survival pathway in endothelial cell [10].
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It is well known that IGF-1 plays an important role for growth and development of human fetus and neonate. In fetal tissues it appears from 9 weeks of gestation and in fetal circulation from 15 weeks [19], and IGF-1 levels rise significantly in the last trimester of pregnancy [20]. A positive correlation of serum IGF-1 with gestational age (GA), birth weight (BW) and intrauterine growth retardation has been demonstrated [21–23]. Some authors think that the change in serum IGF-I levels in very preterm infants was associated with enteral protein intake and weight development and they suggest that high protein and caloric intakes could be useful in obtaining more physiological IGF-1 levels [24]. Experimental results about the effect of orally administered IGF-1 on plasma circulation, IGF-1 level and internal organs are insufficient and inconsistent in different species. Some authors think that orally administered IGF-1 was available in the systemic circulation in mice and in adult rats [25,26] but without any effect on body weight. Other biochemical mediators are also involved in the pathogenesis of ROP, as suggested by experimental trials. Neuropeptide Y (NPY) is an oxygen-induced potent vasoconstrictor and angiogenic agent [27]; angiopoietin 2 [28] and MMP-2 [29] are reported to have an angiogenic role in vivo; HLF and HIF-1a transcription factor which play a role in embryonic vascularization in response to ischemic or hypoxic conditions [30]; estrogen and prolactin seem to be protective against VEGF-induced neovascularization [31,32]. Finally, downregulation of cyclooxygenase-2 could impair VEGF-induced neovascularization in mouse model experimental ROP [33,34]. However, the attempt to reduce COX-2 activity using non-steroidal anti-inflammatory drugs (Ketorolac) did not have positive effects on development and severity of ROP [35]. 3. Risk factors In the past years many causal factors of ROP have been investigated. Prematurity is the main causal factor, as demonstrated by the widely proven correlation among the incidence and severity of ROP and GA [4,36]. Therefore, prematurity is the major pathogenic factor since the adaptive mechanisms of the immature retinal vascular vessels are not suitable to the unfavourable environment of extrauterine life. The role of BW is correlated to GA, but among the same gestational age groups low birth weight is an independent risk factor for developing ROP [37]. Another cause for ROP is the excessive retinal oxygenation [38]. The epidemic of ROP in 1940s to 1950s, the subsequent drastic reduction in incidence after curtailment of oxygen administration [39], the correlation between hyperoxia and ROP [40] and the oxygeninduced ROP in experimental animal models support the oxygen role in the pathogenesis of ROP. On the other hand, keeping babies in low oxygen levels reduced ROP requiring treatment [41] as well as the implementation and enforcement of clinical practices management and monitoring of O2 [42]. Other risk factors for ROP have been previously reported in association with prematurity and low birth weight: hyperglycaemia [43], bacterial and fungal late-onset sepsis [36,44,45], male gender [37] and light exposure [46,47] without univocal results. Moreover, the role of the ethnic and/or genetic predisposition to ROP, although suggestive, is still under investigation [48–50].
Several studies suggested that frequent blood transfusions are closely associated with ROP, but a precise pathogenetic mechanism is not known [51–53]. In the past years, comparing the number of blood transfusions and the amount of blood transfused in 30 very low birth weight infants with ROP and 30 controls, we found that infants with ROP received a significant higher number of blood transfusion and higher amount of blood transfused than infants not developing ROP (7.1 ± 4.4 and 141 ± 77 ml versus 4.0 ± 1.4 and 77 ± 28 ml respectively — p < 0.001) [54]. Currently newborn babies were transfused with packed red blood cells (RBC) from adult donor containing adult hemoglobin. Adult hemoglobin's affinity for oxygen is substantially lower than fetal hemoglobin leading to an increased oxygen delivery to the immature retina. Likewise, mean lifespan of RBC transfused to preterm infants appears to be shorter than in adults, so that relative overload of free iron could be originated by faster breakdown of RBC. Generation of free iron and so increased free radical generation might contribute to retinal damage [55,56], mainly in preterm newborns because of reduced neonatal erythropoiesis and subsequent low employment of free iron [57] and of reduced ferroxidase activity. There is no information whether the influence of RBC transfusions on ROP may be mediated by endocrine factors, but a relationship between blood donor IGF-1 and the development of ROP in transfused premature babies was supposed [58]. All risk factors, both oxygen and not-oxygen-regulated, have been studied considering the whole period from hospital birth to the hospital discharge, but it is possible that postnatal risk factors may be determinant in a time-dependent way. With this hypothesis we studied the known risk factors for ROP, both in 49 infants with severe ROP not requiring any surgery (Group A) and in 44 infants with severe ROP requiring ablative therapy (Group B), in well-defined period in postnatal life: the first two weeks of life, the first month of life, from birth to ROP diagnosis and from ROP diagnosis to pre-threshold ROP. The risk factors considered were: number of blood transfusion and total amount of red blood cells transfused, the use of postnatal steroids, positive blood culture sepsis, candidemia, candida pneumonia, necrotizing enterocolitis requiring surgery, hypotension treated with inotropic drugs, patent ductus arteriosus (PDA) requiring medical or surgical ligation, intraventricular haemorrhage, chronic lung disease, duration of mechanical ventilation, continuous positive airway pressure (CPAP) and oxygen therapy. With respect to the clinical characteristics of study infants, there were significant statistical differences between the groups only with regard to birth weight, due to greater percentage of small-forgestational-age (SGA) in Group B, and to occurrence of chronic lung disease (CLD). As for considered risk factors, duration of mechanical ventilation and of CPAP, PDA requiring treatment, hypotension, necrotizing enterocolitis, and postnatal steroid administration did not result significantly associated with severe ROP at logistic regression analysis. When analysing the first 2 weeks of life (Table 1), the duration of oxygen administration, the number and the total volume of blood transfusions were identified as significant risk factors for progression to threshold ROP. In the first month of life only the duration of oxygen administration, sepsis and the number of blood transfusions maintain statistical significance. Mean time to ROP
Table 1 Time-dependent odd's ratio and interquartile range for ROP risk factors. Risk factors Days on mechanical ventilation Days on oxygen Sepsis Candida pneumonia Number of blood transfusions Volume of blood transfusions (ml/kg)
First two weeks of life
First month of life
1.14 [1.02–1.27] p 0.017
1.08 [1.02–15] p 0.008 2.31 [1.08–4.94] p 0.030
From the birth to diagnosis of ROP
From the diagnosis to pre-threshold ROP 1.00 [1.00–1.01] p 0.022
1.89 [1.23–2.89] p 0.004 1.02 [1.00–1.04] p 0.041
1.91 [1.31–2.8] p 0.001
2.23 9.77 1.61 1.02
[1.10–4.52] [1.02–94.0] [1.20–2.15] [1.00–1.03]
p p p p
0.026 0.048 0.001 0.048
1.82 [1.07–3.01] p 0.027 1.04 [1.00–1.08] p 0.019
C. Romagnoli / Early Human Development 85 (2009) S79–S82
diagnosis from birth was similar in both study groups: 43 ± 10.1 days in not surgical ROP and 44.8 ± 10.1 in severe ROP. In this time frame sepsis, candida pneumonia and blood transfusions were identified as independent risk factors for the progression of ROP to threshold disease. Also mean time from the initial appearance of ROP to prethreshold is almost the same in the two groups: 13 ± 12.9 and 14.4 ± 12.3 days in Group B. When performing logistic regression analysis, only prolonged ventilator use and blood transfusions (number and total amount) were significantly greater in infants who developed surgical ROP as compared to those not requiring surgery. These data suggest that some risk factors for ROP may act in a time-dependent way. Oxygen is critical in the first neonatal period (the first month of life) as well as infection from the 2nd week of life to the time of diagnosis, while blood transfusions are critical from birth to the diagnosis of pre-threshold. 4. Conclusions Analysis of factors involved in the pathogenesis of ROP suggests that their action begins long before anatomical clinical features become appreciable and this is strengthened by the essential role of risk factors from the first two to four weeks of life, thus preventive strategies in very preterm infants should be carried out since birth. According to this perspective and considering the relevance of potentially modifiable factors in developing severe ROP, it is mandatory to suggest: a) a scrupulous administration and monitoring of oxygen, b) a prevention and/or early treatment of systemic infections, c) the need of more restricted blood transfusion guidelines or of new transfusion practices, such as the use of autologous or allogeneic cord blood, and d) the importance of early optimized neonatal nutrition to allow the normal growth and development of newborn infants. Acknowledgement Miss Marta Romagnoli provided assistance for preparing and editing the manuscript. References [1] Chen J, Smith LEH. Retinopathy of prematurity. Angiogenesis 2007;10:133–40. [2] Blair BM, O'halloran HS, Pauly TH, Stevens JL. Decreased incidence of retinopathy of prematurity, 1995–1997. J AAPOS 2001;5:118–22. [3] Bullard SR, Donahue SP, Feman SS, Sinatra BB, Walsh WF. The decreasing incidence and severity of retinopathy of prematurity. J AAPOS 1999;3:46–52. [4] Giannantonio C, Papacci P, Molle F, Lepore D, Gallini F, Romagnoli C. An epidemiologic analysis of retinopathy of prematurity over 10 years. J Pediatr Ophthalmol Strabismus 2008;45:162–7. [5] Todd DA, Wright A, Smith J, the NICUS Group. Severe retinopathy of prematurity in infants ,30 weeks' gestation in New South Wales and the Australian Capital Territory from 1992 to 2002. Arch Dis Child Fetal Neonatal Ed 2007;92:F251–4. [6] Hellstrom A, Engstrom E, Hard A-L, Albertsson-Wikland K, Carlsson B, Niklasson A, et al. Postnatal serum insulin-like growth factor I deficiency is associated with retinopathy of prematurity and other complications of premature birth. Pediatrics 2003;112:1016–20. [7] Smith LEH. Pathogenesis of retinopathy of prematurity. Semin Neonatol 2003;8: 469–73. [8] Pierce EA, Foley ED, Smith LEH. Regulation of vascular endothelial growth factor by oxygen in a model of retinopathy of prematurity. Arch Ophthalmol 1996;114: 1219–28. [9] Alon T, Hemo I, Itin A, Pe'er J, Stone J, Keshet E. Vascular endothelial growth factor acts as a survival factor for newly formed retinal vessels and has implications for retinopathy of prematurity. Nat Med 1995;1:1024–8. [10] Hellstrom A, Perruzzi C, Ju M, Engstrom E, Hard AL, Liu JL, et al. Low IGF-I suppresses VEGF-survival signaling in retinal endothelial cells: direct correlation with clinical retinopathy of prematurity. Proc Natl Acad Sci USA 2001;98:5804–8. [11] Mintz-Hittner HA, Kuffel RR. Intravitreal injection of bevacizumab (Avastin) for treatment of stage 3 retinopathy of prematurity in zone I or posterior zone II. Retina 2008;28:831–8. [12] Chung EJ, Kim JH, Ahn HS, Koh HJ. Combination of laser photocoagulation and intravitreal bevacizumab(avastin) for aggressive zone 1 ROP. Graefe's Arch Clin Exp Ophthalmol 2007;245:1727–30. [13] Kusaka S, Shima C, Wada K, Arahori H, Shimojyo H, Sato T, et al. Efficacy of intravitreal injection of bevacizumab for severe retinopathy of prematurity a pilot study. Br J Ophthalmol 2008;92:1450–5.
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Contents lists available at ScienceDirect
Early Human Development j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / e a r l h u m d ev
Risk factors and growth factors in ROP C. Romagnoli Division of Neonatology, Catholic University of Rome, Largo A. Gemelli, 8 00168, Rome, Italy
a r t i c l e
i n f o
Keywords: Retinopathy of prematurity Vascular growth factors Blood transfusion Infection
a b s t r a c t Retinopathy of prematurity (ROP) is a multifactorial disease which incidence is increasing with increasing survival of very preterm infants. Pathogenic pathway is characterised by abnormal retinal vascular development modulated by vascular growth factors: low IGF-1 in the first phase and high VEGF in the second phase. Many causal factors are able to influence retinal vascularization: gestational age, birth weight, oxygen administration, perinatal bacterial or fungal infections, and blood transfusions. All risk factors, both oxygen and not-oxygen-regulated, have been studied considering the whole period from hospital birth to the hospital discharge, but it is possible that postnatal risk factors may be determinant in a time-dependent way. Analysis of factors involved in the pathogenesis of ROP suggests that their action begins long before anatomical clinical features become appreciable and this is strengthened by the essential role of risk factors from the first two to four weeks of life, thus preventive strategies in very preterm infants should be carried out since birth. © 2009 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Retinopathy of prematurity (ROP) is a multifactorial disease that affects premature infants and it remains a major cause of blindness and visual impairment despite of continuous improvements in neonatal care [1]. Data on the incidence of ROP in industrialized countries within the past decade are controversial and, although some studies show a decline in incidence and severity of the disease, recent reports show a greater occurrence of more severe ROP [2–5]. Pathogenic pathway is characterised by abnormal retinal vascular development modulated by vascular growth factors according to molecular model organised in two distinct phases: “Phase I” involving delayed retinal vascular growth after premature birth and “Phase II” concerning uncontrolled proliferative growth of retinal blood vessels [6,7]. Growth factors as well as biochemical mediators are involved in this complex pathogenic mechanism and also clinical risk factors are correlated with development of ROP. 2. Growth factors Recent research data suggest a significant role of vascular endothelial growth factor (VEGF) and of insulin-like growth factor 1 (IGF-1) in the pathogenesis of ROP [6,7]. VEGF is involved in retinal vascular development and it is expressed in response to hypoxia. In normal condition neural retina develops anterior to the vasculature and the subsequent localized hypoxia stimulates production of VEGF anterior to the developing vessels. After premature birth, in phase I of ROP the sudden postnatal increase of tissue oxygen tension
E-mail address: [email protected]. 0378-3782/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.earlhumdev.2009.08.026
(physiological or iatrogenic) suppresses the VEGF mRNA expression and the normal VEGF-driven vascular growth and it promotes apoptosis of vascular endothelial cells and vaso-obliteration [8,9]. However, in the phase I, development of normal neural retina occurs allowing non-vascularized retina to become hypoxic. At this time VEGF accumulation occurs anterior to the vasculature, but VEGF is not able to stimulate angiogenesis because of lack of IGF-1 that exerts a permissive role in VEGF-induced neovascularization. In other words the low levels of IGF-1 in phase I of ROP inhibit VEGF activity in order to prevent normal survival of vascular endothelial cells [10] and to inhibit normal retinal vascularization. This allows the neural retina to develop under hypoxic condition and to induce more VEGF production and accumulation. This overproduction of VEGF, at a determined postmenstrual age (30–31 weeks) when IGF-1 increases and reaches normal levels, induces an uncontrolled neovascularization that may lead to retinal detachment. In this phase of ROP the role of VEGF is verified also by reports on the positive effects of anti-VEGF drugs (Bevacizumab) in controlling neovascularization [11–15]. This complex mechanism is reported by many clinical and experimental observations. Firstly, it is well known that patients with genetic defects in the GH/IGF-1 axis show an abnormal retinal vascularization characterised by few vascular branching vessels [16]. Moreover, the retinal blood vessels grow more slowly in IGF-1-null mice than in those normal. Secondly, it has been demonstrated a direct relationship between serum levels of IGF-1 and developing ROP and severity. Preterm infants developing ROP showed lower serum IGF-1 levels as compared with infants without ROP, and the duration of low IGF-1 levels correlated strongly with the severity of ROP [5,17,18]. Finally, it has been demonstrated that IGF-1 is able to control maximum VEGF activation of the Akt survival pathway in endothelial cell [10].
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It is well known that IGF-1 plays an important role for growth and development of human fetus and neonate. In fetal tissues it appears from 9 weeks of gestation and in fetal circulation from 15 weeks [19], and IGF-1 levels rise significantly in the last trimester of pregnancy [20]. A positive correlation of serum IGF-1 with gestational age (GA), birth weight (BW) and intrauterine growth retardation has been demonstrated [21–23]. Some authors think that the change in serum IGF-I levels in very preterm infants was associated with enteral protein intake and weight development and they suggest that high protein and caloric intakes could be useful in obtaining more physiological IGF-1 levels [24]. Experimental results about the effect of orally administered IGF-1 on plasma circulation, IGF-1 level and internal organs are insufficient and inconsistent in different species. Some authors think that orally administered IGF-1 was available in the systemic circulation in mice and in adult rats [25,26] but without any effect on body weight. Other biochemical mediators are also involved in the pathogenesis of ROP, as suggested by experimental trials. Neuropeptide Y (NPY) is an oxygen-induced potent vasoconstrictor and angiogenic agent [27]; angiopoietin 2 [28] and MMP-2 [29] are reported to have an angiogenic role in vivo; HLF and HIF-1a transcription factor which play a role in embryonic vascularization in response to ischemic or hypoxic conditions [30]; estrogen and prolactin seem to be protective against VEGF-induced neovascularization [31,32]. Finally, downregulation of cyclooxygenase-2 could impair VEGF-induced neovascularization in mouse model experimental ROP [33,34]. However, the attempt to reduce COX-2 activity using non-steroidal anti-inflammatory drugs (Ketorolac) did not have positive effects on development and severity of ROP [35]. 3. Risk factors In the past years many causal factors of ROP have been investigated. Prematurity is the main causal factor, as demonstrated by the widely proven correlation among the incidence and severity of ROP and GA [4,36]. Therefore, prematurity is the major pathogenic factor since the adaptive mechanisms of the immature retinal vascular vessels are not suitable to the unfavourable environment of extrauterine life. The role of BW is correlated to GA, but among the same gestational age groups low birth weight is an independent risk factor for developing ROP [37]. Another cause for ROP is the excessive retinal oxygenation [38]. The epidemic of ROP in 1940s to 1950s, the subsequent drastic reduction in incidence after curtailment of oxygen administration [39], the correlation between hyperoxia and ROP [40] and the oxygeninduced ROP in experimental animal models support the oxygen role in the pathogenesis of ROP. On the other hand, keeping babies in low oxygen levels reduced ROP requiring treatment [41] as well as the implementation and enforcement of clinical practices management and monitoring of O2 [42]. Other risk factors for ROP have been previously reported in association with prematurity and low birth weight: hyperglycaemia [43], bacterial and fungal late-onset sepsis [36,44,45], male gender [37] and light exposure [46,47] without univocal results. Moreover, the role of the ethnic and/or genetic predisposition to ROP, although suggestive, is still under investigation [48–50].
Several studies suggested that frequent blood transfusions are closely associated with ROP, but a precise pathogenetic mechanism is not known [51–53]. In the past years, comparing the number of blood transfusions and the amount of blood transfused in 30 very low birth weight infants with ROP and 30 controls, we found that infants with ROP received a significant higher number of blood transfusion and higher amount of blood transfused than infants not developing ROP (7.1 ± 4.4 and 141 ± 77 ml versus 4.0 ± 1.4 and 77 ± 28 ml respectively — p < 0.001) [54]. Currently newborn babies were transfused with packed red blood cells (RBC) from adult donor containing adult hemoglobin. Adult hemoglobin's affinity for oxygen is substantially lower than fetal hemoglobin leading to an increased oxygen delivery to the immature retina. Likewise, mean lifespan of RBC transfused to preterm infants appears to be shorter than in adults, so that relative overload of free iron could be originated by faster breakdown of RBC. Generation of free iron and so increased free radical generation might contribute to retinal damage [55,56], mainly in preterm newborns because of reduced neonatal erythropoiesis and subsequent low employment of free iron [57] and of reduced ferroxidase activity. There is no information whether the influence of RBC transfusions on ROP may be mediated by endocrine factors, but a relationship between blood donor IGF-1 and the development of ROP in transfused premature babies was supposed [58]. All risk factors, both oxygen and not-oxygen-regulated, have been studied considering the whole period from hospital birth to the hospital discharge, but it is possible that postnatal risk factors may be determinant in a time-dependent way. With this hypothesis we studied the known risk factors for ROP, both in 49 infants with severe ROP not requiring any surgery (Group A) and in 44 infants with severe ROP requiring ablative therapy (Group B), in well-defined period in postnatal life: the first two weeks of life, the first month of life, from birth to ROP diagnosis and from ROP diagnosis to pre-threshold ROP. The risk factors considered were: number of blood transfusion and total amount of red blood cells transfused, the use of postnatal steroids, positive blood culture sepsis, candidemia, candida pneumonia, necrotizing enterocolitis requiring surgery, hypotension treated with inotropic drugs, patent ductus arteriosus (PDA) requiring medical or surgical ligation, intraventricular haemorrhage, chronic lung disease, duration of mechanical ventilation, continuous positive airway pressure (CPAP) and oxygen therapy. With respect to the clinical characteristics of study infants, there were significant statistical differences between the groups only with regard to birth weight, due to greater percentage of small-forgestational-age (SGA) in Group B, and to occurrence of chronic lung disease (CLD). As for considered risk factors, duration of mechanical ventilation and of CPAP, PDA requiring treatment, hypotension, necrotizing enterocolitis, and postnatal steroid administration did not result significantly associated with severe ROP at logistic regression analysis. When analysing the first 2 weeks of life (Table 1), the duration of oxygen administration, the number and the total volume of blood transfusions were identified as significant risk factors for progression to threshold ROP. In the first month of life only the duration of oxygen administration, sepsis and the number of blood transfusions maintain statistical significance. Mean time to ROP
Table 1 Time-dependent odd's ratio and interquartile range for ROP risk factors. Risk factors Days on mechanical ventilation Days on oxygen Sepsis Candida pneumonia Number of blood transfusions Volume of blood transfusions (ml/kg)
First two weeks of life
First month of life
1.14 [1.02–1.27] p 0.017
1.08 [1.02–15] p 0.008 2.31 [1.08–4.94] p 0.030
From the birth to diagnosis of ROP
From the diagnosis to pre-threshold ROP 1.00 [1.00–1.01] p 0.022
1.89 [1.23–2.89] p 0.004 1.02 [1.00–1.04] p 0.041
1.91 [1.31–2.8] p 0.001
2.23 9.77 1.61 1.02
[1.10–4.52] [1.02–94.0] [1.20–2.15] [1.00–1.03]
p p p p
0.026 0.048 0.001 0.048
1.82 [1.07–3.01] p 0.027 1.04 [1.00–1.08] p 0.019
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diagnosis from birth was similar in both study groups: 43 ± 10.1 days in not surgical ROP and 44.8 ± 10.1 in severe ROP. In this time frame sepsis, candida pneumonia and blood transfusions were identified as independent risk factors for the progression of ROP to threshold disease. Also mean time from the initial appearance of ROP to prethreshold is almost the same in the two groups: 13 ± 12.9 and 14.4 ± 12.3 days in Group B. When performing logistic regression analysis, only prolonged ventilator use and blood transfusions (number and total amount) were significantly greater in infants who developed surgical ROP as compared to those not requiring surgery. These data suggest that some risk factors for ROP may act in a time-dependent way. Oxygen is critical in the first neonatal period (the first month of life) as well as infection from the 2nd week of life to the time of diagnosis, while blood transfusions are critical from birth to the diagnosis of pre-threshold. 4. Conclusions Analysis of factors involved in the pathogenesis of ROP suggests that their action begins long before anatomical clinical features become appreciable and this is strengthened by the essential role of risk factors from the first two to four weeks of life, thus preventive strategies in very preterm infants should be carried out since birth. According to this perspective and considering the relevance of potentially modifiable factors in developing severe ROP, it is mandatory to suggest: a) a scrupulous administration and monitoring of oxygen, b) a prevention and/or early treatment of systemic infections, c) the need of more restricted blood transfusion guidelines or of new transfusion practices, such as the use of autologous or allogeneic cord blood, and d) the importance of early optimized neonatal nutrition to allow the normal growth and development of newborn infants. Acknowledgement Miss Marta Romagnoli provided assistance for preparing and editing the manuscript. References [1] Chen J, Smith LEH. Retinopathy of prematurity. Angiogenesis 2007;10:133–40. [2] Blair BM, O'halloran HS, Pauly TH, Stevens JL. Decreased incidence of retinopathy of prematurity, 1995–1997. J AAPOS 2001;5:118–22. [3] Bullard SR, Donahue SP, Feman SS, Sinatra BB, Walsh WF. The decreasing incidence and severity of retinopathy of prematurity. J AAPOS 1999;3:46–52. [4] Giannantonio C, Papacci P, Molle F, Lepore D, Gallini F, Romagnoli C. An epidemiologic analysis of retinopathy of prematurity over 10 years. J Pediatr Ophthalmol Strabismus 2008;45:162–7. [5] Todd DA, Wright A, Smith J, the NICUS Group. Severe retinopathy of prematurity in infants ,30 weeks' gestation in New South Wales and the Australian Capital Territory from 1992 to 2002. Arch Dis Child Fetal Neonatal Ed 2007;92:F251–4. [6] Hellstrom A, Engstrom E, Hard A-L, Albertsson-Wikland K, Carlsson B, Niklasson A, et al. Postnatal serum insulin-like growth factor I deficiency is associated with retinopathy of prematurity and other complications of premature birth. Pediatrics 2003;112:1016–20. [7] Smith LEH. Pathogenesis of retinopathy of prematurity. Semin Neonatol 2003;8: 469–73. [8] Pierce EA, Foley ED, Smith LEH. Regulation of vascular endothelial growth factor by oxygen in a model of retinopathy of prematurity. Arch Ophthalmol 1996;114: 1219–28. [9] Alon T, Hemo I, Itin A, Pe'er J, Stone J, Keshet E. Vascular endothelial growth factor acts as a survival factor for newly formed retinal vessels and has implications for retinopathy of prematurity. Nat Med 1995;1:1024–8. [10] Hellstrom A, Perruzzi C, Ju M, Engstrom E, Hard AL, Liu JL, et al. Low IGF-I suppresses VEGF-survival signaling in retinal endothelial cells: direct correlation with clinical retinopathy of prematurity. Proc Natl Acad Sci USA 2001;98:5804–8. [11] Mintz-Hittner HA, Kuffel RR. Intravitreal injection of bevacizumab (Avastin) for treatment of stage 3 retinopathy of prematurity in zone I or posterior zone II. Retina 2008;28:831–8. [12] Chung EJ, Kim JH, Ahn HS, Koh HJ. Combination of laser photocoagulation and intravitreal bevacizumab(avastin) for aggressive zone 1 ROP. Graefe's Arch Clin Exp Ophthalmol 2007;245:1727–30. [13] Kusaka S, Shima C, Wada K, Arahori H, Shimojyo H, Sato T, et al. Efficacy of intravitreal injection of bevacizumab for severe retinopathy of prematurity a pilot study. Br J Ophthalmol 2008;92:1450–5.
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