Retinopathy of prematurity (ROP) is a leading cause of blindness affecting approximately 50,000 children worldwide.1,2 The disease is caused by abnormal vascular proliferation of the developing retina and increasing evidence supports that it is a multifactorial disease. Although most cases regress, ROP may progress to severe ROP, which is associated with an increased risk of blindness due to retinal detachment. Other complications may include macular folds, refractive amblyopia, and strabismic amblyopia.3–7 Early detection of severe ROP and assessing risk factors allow specific treatment intervention to be implemented, decreasing the severity of ROP sequelae and reducing unfavorable outcomes.8
Reports about the incidence of ROP vary; it may be increasing because of increased survival of extremely preterm infants.9,10 On the other hand, some studies have reported that advances in neonatal care have decreased the overall incidence of ROP.11,12 Studies have also documented many associated risk factors for ROP, such as gestational age, birth weight, oxygen supplementation, intraventricular hemorrhage, sepsis, and blood transfusion.13–22
The aim of the current retrospective study was to identify the incidence of ROP and the associated risk factors of ROP in the second largest Canadian neonatal intensive care unit from July 2006 to July 2010. We identified baseline characteristics, demographic information, and comorbidities, and analyzed the association with ROP by univariate and multivariate logistic regression models.
Patients and Methods
The retrospective chart study was conducted at McMaster Hospital between July 2006 and July 2010. Data were extracted from The Canadian Neonatal Network, which is the national registry that maintains clinical information about neonates. Approval for this study was obtained from the Health Research Ethics Board.
All infants admitted to the neonatal intensive care unit with a birth weight less than 1,500 g or gestational age less than 32 weeks were screened for ROP. Additional infants weighing more than 1,500 g, gestational age greater than 32 weeks, or both were screened, following a special request from the attending neonatologist based on an increased perceived risk. Infants born with gestational age of 27 weeks or less were first examined at 31 weeks postmenstrual age. Beyond 27 weeks gestational age, the first examination was performed 4 weeks after birth.
The examination was performed under topical anesthesia using 0.5% proparacaine eye drops and supportive oral sucrose. Pupils were dilated using a topical administration of two drops of cyclopentolate 0.2% and phenylephrine 1% (Alcon Laboratories, Inc., Mississauga, Ontario) at 10-minute intervals. Indirect ophthalmoscopy was performed using a binocular indirect ophthalmoscope and 28 diopter lens. An infant speculum and scleral depressor were also used to perform the examination. ROP status was documented using the International Classification of ROP, including stage, zone, and extent of disease and presence or absence of plus disease.23,24 Infants with ROP were routinely examined every 1 to 2 weeks, but some infants were examined as frequently as twice per week or as infrequently as once every 3 weeks depending on the zone and severity of ROP.25
Interobserver variation of examination results is minimal because more than 90% of screening examinations during this time period were performed by a single physician (GI). Infants requiring laser photocoagulation treatment were transferred to another hospital for the procedure and most were readmitted to our hospital following treatment. Treatment was determined following the Early Treatment for Retinopathy of Prematurity Study criteria.8,26
For analysis, the highest stage or most severe ROP in either eye for an individual infant was recorded. Severe ROP was defined in this study as stage 3 ROP or worse. Infants were placed in one of five gestational age and birth weight groups for purposes of comparison. These groups were assigned based on the results of other studies for ease of comparison, and to provide an even distribution of data obtained in this study. Risk factors such as gestational age, birth weight, intraventricular hemorrhage, patent ductus arteriosus, necrotizing enterocolitis, oxygen therapy, perinatal infection, blood transfusion, and gender were extracted from the database for comparison of screened infants who had ROP and those who did not.
Oxygen therapy protocols were defined by the neonatal intensive care unit. For infants of 32 weeks gestational age or less, the high saturation limit on oxygen is 93% and the low saturation limit is 84%. On room air, the high saturation limit on oxygen is 100% and the low saturation limit is 84%. For infants of 33 to 37 weeks gestational age, the saturation limits on oxygen range from 88% to 95%. On room air, the high saturation limit on oxygen is 100% and the low saturation limit is 88%. These parameters have been employed in the unit to limit oxygen’s influence as a risk factor for the development of ROP.
Statistical analysis was performed using SPSS software (version 17.0; SPSS, Inc., Chicago, IL). To assess the statistical significance of gestational age groups as predictors for the incidence of ROP, a univariate analysis was conducted with the reference group being gestational age of 31 weeks or greater. The same process was completed for establishing a relationship between birth weight groups and incidence of ROP, with the reference group being birth weight of 1,500 g or greater. To assess other potential risk factors for developing ROP, such as gender, oxygen therapy, perinatal infection, transfusions, intraventricular hemorrhage, patent ductus arteriosus, and necrotizing enterocolitis, univariate analysis was conducted, with evaluation of odds ratios and confidence intervals. To control all of these variables and estimate the independent risk factors for incidence of ROP, the previously mentioned risk factors were entered into a logistic regression multivariate analysis. P values, odd ratios, and confidence intervals were extracted for all nine variables of interest.
From July 2006 to July 2010, there were 503 infants eligible for ROP screening in the neonatal intensive care unit. Fifteen infants were discharged prior to inpatient eye screening. Sixty-five infants were excluded due to incomplete eye examination data as a result of the infant not surviving to the time of screening. Therefore, during the study period, 423 infants fulfilled the inclusion criteria, having complete clinical data, and were included in this analysis.
Among the entire group of 503 infants, 113 (23%) were born in Hamilton and the rest (77%) were referred from other regions (Niagara 20%, Waterloo 18%, Grand River 13%, Halton 11%, Wellington 6%, Greater Toronto Area 4%, and other regions 5%). Fifty-seven percent of the infants were male.
For the entire cohort, the overall incidence of any ROP was 40.4% (171 of 423 infants). The mean gestational age was 27.5 weeks (range: 23 to 36 weeks) at birth, 26 weeks (range: 23 to 31 weeks) for infants with ROP, 25.2 weeks (range: 23 to 28 weeks) for infants with severe ROP, and 28.5 weeks (range: 24 to 36 weeks) for infants without ROP. All 171 infants with ROP had a gestational age of 31 weeks or less. Table 1 displays the stages of ROP by gestational age.
Table 1: Stages of ROP by Gestational Age
The mean overall birth weight was 1,054 g (range: 470 to 2,460 g). The mean birth weight in infants with ROP was 840 g (range: 500 to 1,890 g), which was significantly lower than in the infants without ROP, whose mean birth weight was 1,191 g (range: 470 to 2,460 g) (P < .001). Two hundred fourteen infants (50.5%) were classified as having extremely low birth weight (ELBW [defined as birth weight less than 1,000 g]), of whom 138 (64.4%) had ROP. Eighty-five infants (20%) had birth weight of 750 g or less, of whom 85.8% had ROP. ROP was present in no infants with birth weight of 1,890 g or greater and in only 0.59% of infants with birth weight greater than 1,500 g. Of the infants who had ROP, 80% (137 of 171 infants) had a birth weight of 1,000 g or less. The mean birth weight in infants with severe ROP was 730.3 g (range: 500 to 1,095 g). Table 2 displays the stages of ROP by birth weight.
Table 2: Stages of ROP by Birth Weight
The overall incidence of severe ROP was 9.2% (39 infants). The overall incidence of laser treatment was 5.67% (24 infants). All infants were sent to other hospitals for laser treatment. Only one infant developed stage 4 ROP and none developed stage 5 ROP during the study period.
Three hundred fifty-one infants underwent mechanical ventilation therapy at least once during their stay at the neonatal intensive care unit, 165 infants had perinatal infection, 262 infants received transfusion of any blood product, 174 had intraventricular hemorrhage, 150 had patent ductus arteriosus, and 18 had necrotizing enterocolitis. Perinatal risk factors for ROP are summarized in Table 3. Multivariate analysis showed that gestational age, birth weight, presence of necrotizing enterocolitis, and number of days on mechanical ventilation therapy were independently associated with ROP in order of significance based on P values. This logistic regression demonstrated that the most significant adjusted risk factors for ROP were gestational age (odds ratio: 2.64, 95% confidence interval; 1.73 to 4.03) and birth weight (odds ratio: 1.90, 95% confidence interval 1.34 to 2.69).
Table 3: Univariate and Multivariate Determinants of ROP
The incidence of ROP has varied considerably over time. There have been reports about decrease, no change, and increase in the ROP incidence.11,12,27,28–32 It has been difficult to compare results because data availability, screening criteria methods, ethnicity, geographical location, risk factors, survival rate, and neonatal standards of care vary between studies.1,32
The overall ROP incidence in the current study was 40.4%. The Cryotherapy for Retinopathy of Prematurity Study33 reported an ROP incidence of 65.8% in infants with birth weight less than 1,251 g; a similar ROP incidence of 68% was reported from the Early Treatment for Retinopathy of Prematurity Study26,34,35 in infants having a similar birth weight. Comparison of the Cryotherapy for Retinopathy of Prematurity and Early Treatment for Retinopathy of Prematurity data with our study is limited because our study was based on a small sample size. The high percentage of stages 1 and 2 in our study may indicate that more instances of earlier ROP stages were observed and documented and may explain the overall incidence found in this study.
Other studies performed in developed countries in infants with birth weight less than 1,000 g have shown that the overall ROP incidence varies between 47.3% and 82.5% and severe ROP incidence varies between 21.6% and 43.3%. A study by Hoogerwerf et al.20 of infants with a birth weight less than 1,500 g reported an incidence of overall ROP of 23.3% and an incidence of severe ROP of 1.2%, both lower than the findings of the current study. A possible explanation is the higher percentage of infants with ELBW found in our study compared to their study (50.5% vs 35%). In addition, the infants in our study had a lower mean gestational age (27.5 vs 29.4 weeks) and birth weight (1,054 vs 1,177 g), respectively.
The study by Dhaliwal et al.36 of infants with a birth weight less than 1,500 g, found a lower overall ROP incidence compared to our study (17% vs 40.4%) but the incidence of severe ROP and treatment were similar to our study (9% vs 8.5% and 5% vs 5.6%, respectively). Our study also had a higher percentage of infants with ELBW (50.5% vs 27.6%) and smaller and younger infants compared to their study: mean gestational age (27.6 vs 29 weeks) and mean birth weight (1,054 g vs 1,240 g).
Gilbert et al.37 compared gestational age and birth weight between countries with low, moderate, and high levels of development. In highly developed countries, they found that all infants with severe ROP had a mean gestational age less than 26 weeks and a mean birth weight less than 800 g, similar to the mean gestational age and birth weight found in infants with severe ROP in our study (25 weeks and 730 g, respectively). Our study showed a significant relation between gestational age and birth weight with ROP. Birth weight and gestational age in the ROP group were significantly lower than in the non-ROP group. This is consistent with other studies where birth weight and gestational age have been widely reported as important factors associated with ROP.
In the literature there have been numerous investigators who studied the perinatal comorbidity risk factors, beyond birth weight and gestational age, that predispose to or influence the development of ROP. These factors may contribute to ROP independently or produce an effect by interrelated or additive means. Our sample size did not allow for analysis of additive risk factors, but did find that gestational age, birth weight, presence of necrotizing enterocolitis, and the number of days on mechanical ventilation therapy were independently associated with the development of any ROP.
Mechanical ventilation delivers oxygen into the lungs at a positive pressure and a longer exposure to high oxygen pressure may contribute to ROP development. Shah et al. also determined that mechanical ventilation could be a risk factor for ROP.38 Recently, Giannantonio et al. published their findings of ROP risk factors and noted that prolonged mechanical ventilation was also associated with ROP requiring treatment.39 Interestingly, Fortes Filho et al. found mechanical ventilation to be a significant risk factor only for the development of any ROP in infants with a gestational age of 32 weeks or greater.40 They concluded that although infants with a lower gestational age are challenged with consequences of general immaturity, larger infants with higher gestational age tend to be ‘sicker’ with more comorbidities.
Necrotizing enterocolitis has been considered as a possible risk factor in other studies of ROP development. Kumar et al. found that necrotizing enterocolitis was a significant risk factor for severe ROP on univariate analysis.41 Giapros et al. found necrotizing enterocolitis in 8.3% of infants with any ROP and 4.5% in their study of 247 infants with gestational age less than 33 weeks and birth weight less than 1,501 g.42 We found a similar number of patients with necrotizing enterocolitis who had any ROP (8.2%), but our non-ROP group only had 1.6% infants with necrotizing enterocolitis.
We acknowledge the limitations of our study. First, the study was conducted among inpatients at a neonatal intensive care unit and thus could misrepresent the general incidence of ROP. Second, our infants were referred to other hospitals when laser photocoagulation therapy was indicated and, although most infants came back to our hospital for follow-up, we were unable to access complete follow-up data for transferred patients, which may have resulted in a possible overestimation or underestimation of the true incidence of laser therapy and retina surgery. Given that 13% (65 of 503 patients) of our original population were excluded as a result of not surviving to the time of screening, the true incidence of ROP could be higher. Furthermore, our screening criteria were more inclusive than the recent American Academy of Pediatrics recommendation for screening at gestational age less than 30 weeks and birth weight less than 1,500 g. This may have also underestimated our incidence of ROP by increasing the number of unaffected patients.
The current retrospective study of 423 infants represents one of the few studies of incidence and associated risk factors of ROP performed at a Canadian tertiary care center. Our results confirm the influence of extreme prematurity, low gestational age, and birth weight on the incidence of ROP. Although our study had a high percentage of infants with ELBW, born most prematurely, we did not find an associated increase in the incidence of severe ROP and treatment. We believe that a better understanding of ROP pathogenesis and the development of site-specific strategies for the treatment of premature infants and associated clinical conditions may decrease the incidence of severe ROP and the need for treatment.
- Gilbert C. Retinopathy of prematurity: a global perspective of the epidemics, population of babies at risk and implications for control. Early Hum Dev. 2008;84:77–82. doi:10.1016/j.earlhumdev.2007.11.009 [CrossRef]
- Zin AA, Moreira ME, Bunce C, Darlow BA, Gilbert CE. Retinopathy of prematurity in 7 neonatal units in Rio de Janeiro: screening criteria and workload implications. Pediatrics. 2010;126:e410–e417. doi:10.1542/peds.2010-0090 [CrossRef]
- Bremer DL, Palmer EA, Fellows RR, et al. Strabismus in premature infants in the first year of life. Arch Ophthalmol. 1998;116:329–333.
- Repka MX, Summers CG, Palmer EA, Dobson V, Tung B, Davis B. The incidence of ophthalmologic interventions in children with birth weights less than 1251 grams: results through 5 1/2 years. Ophthalmology. 1998;105:1621–1627. doi:10.1016/S0161-6420(98)99028-5 [CrossRef]
- Quinn GE, Dobson V, Kivlin J, et al. Prevalence of myopia between 3 months and 5 1/2 years in preterm infants with and without retinopathy of prematurity. Ophthalmology. 1998;105:1292–1300. doi:10.1016/S0161-6420(98)97036-1 [CrossRef]
- Fielder AR. The natural ocular outcome of premature birth and retinopathy: status at 1 year. Arch Ophthalmol. 1995;113:850–851. doi:10.1001/archopht.1995.01100070020008 [CrossRef]
- Cryotherapy for Retinopathy of Prematurity Cooperative Group. Multicenter trial of cryotherapy for retinopathy of prematurity: natural history ROP: ocular outcome at 5(1/2) years in premature infants with birth weights less than 1251 g. Arch Ophthalmol. 2002;120:595–599.
- Early Treatment for Retinopathy of Prematurity Cooperative Group. Revised indications for the treatment of retinopathy of prematurity: results of the Early Treatment for Retinopathy of Prematurity randomized trial. Arch Ophthalmol. 2003;121:1684–1694.
- Hameed B, Shyamanur K, Kotecha S, et al. Trends in the incidence of severe retinopathy of prematurity in a geographically defined population over a 10-year period. Pediatrics. 2004;113:1653–1657. doi:10.1542/peds.113.6.1653 [CrossRef]
- Schiariti V, Matsuba C, Houbé JS, Synnes AR. Severe retinopathy of prematurity and visual outcomes in British Columbia: a 10-year analysis. J Perinatal. 2008;28:566–572. doi:10.1038/jp.2008.34 [CrossRef]
- Bullard SR, Donahue SP, Feman SS, Sinatra RB, Walsh WF. The decreasing incidence and severity of retinopathy of prematurity. J AAPOS. 1999;3:46–52. doi:10.1016/S1091-8531(99)70094-7 [CrossRef]
- 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. doi:10.1016/j.ophtha.2003.10.030 [CrossRef]
- Ebrahim M, Ahmad RS, Mohammad M. Incidence and risk factors of retinopathy of prematurity in Babol, North of Iran. Ophthalmic Epidemiol. 2010;17:166–170. doi:10.3109/09286581003734860 [CrossRef]
- Romagnoli C. Risk factors and growth factors in ROP. Early Hum Dev. 2009;85:S79–S82. doi:10.1016/j.earlhumdev.2009.08.026 [CrossRef]
- Liu L, Tian T, Zheng C-X, et al. Risk factors and laser therapy for retinopathy of prematurity in neonatal intensive care unit. World J Pediatr. 2009;5:304–307. doi:10.1007/s12519-009-0058-6 [CrossRef]
- Lad EM, Hernandez-Boussard T, Morton JM, Moshfeghi DM. Incidence of retinopathy of prematurity in the United States: 1997 through 2005. Am J Ophthalmol. 2009;148:451–458. doi:10.1016/j.ajo.2009.04.018 [CrossRef]
- Hirabayashi H, Honda S, Morioka I, et al. Inhibitory effects of maternal smoking on the development of severe retinopathy of prematurity. Eye (Lond). 2009;24:1024–1027. doi:10.1038/eye.2009.263 [CrossRef]
- Fortes Filho JB, Eckert GU, Valiatti FB, Dos Santos PG, da Costa MC, Procianoy RS. The influence of gestational age on the dynamic behavior of other risk factors associated with retinopathy of prematurity (ROP). Graefes Arch Clin Exp Ophthalmol. 2009;248:893–900. doi:10.1007/s00417-009-1248-6 [CrossRef]
- Choo MM, Martin FJ, Theam LC, U-Teng C. Retinopathy of prematurity in extremely low birth weight infants in Malaysia. J AAPOS. 2009;13:446–449. doi:10.1016/j.jaapos.2009.06.008 [CrossRef]
- Hoogerwerf A, Schalij-Delfos NE, van Schooneveld MJ, Termote JU. Incidence of retinopathy of prematurity over the last decade in the Central Netherlands. Neonatology. 2010;98:137–142. doi:10.1159/000280386 [CrossRef]
- Wani VB, Kumar N, Sabti K, et al. Results of screening for retinopathy of prematurity in a large nursery in Kuwait: incidence and risk factors. Indian J Ophthalmol. 2010;58:204–208. doi:10.4103/0301-4738.62644 [CrossRef]
- Express Group. Incidence of and risk factors for neonatal morbidity after active perinatal care: Extremely Preterm Infants Study in Sweden (EXPRESS). Acta Paediatr. 2010;99:978–992.
- Flynn JT. An international classification of retinopathy of prematurity: development of the classification of the late stages of retinopathy of prematurity. Birth Defects Orig Artic Ser. 1988;24:175–183.
- International Committee for the Classification of Retinopathy of Prematurity. The international classification of retinopathy of prematurity revisited. Arch Ophthalmol. 2005;123:991–999.
- Reynolds JD, Dobson V, Quinn GE, et al. Evidence-based screening criteria for retinopathy of prematurity: natural history data from the CRYO-ROP and LIGHT-ROP studies. Arch Ophthalmol. 2002;120:1470–1476.
- Good WV, Hardy RJ, Dobson V, et al. The incidence and course of retinopathy of prematurity: findings from the Early Treatment for Retinopathy of Prematurity study. Pediatrics. 2005;116:15–23. doi:10.1542/peds.2004-1413 [CrossRef]
- Binkhathlan AA, Almahmoud LA, Saleh MJ, Srungeri S. Retinopathy of prematurity in Saudi Arabia: incidence, risk factors, and the applicability of current screening criteria. Br J Ophthalmol. 2008;92:167–169. doi:10.1136/bjo.2007.126508 [CrossRef]
- Blair BM, O’Halloran HS, Pauly TH, Stevens JL. Decreased incidence of retinopathy of prematurity, 1995–1997. J AAPOS. 2001;5:118–122. doi:10.1067/mpa.2001.113843 [CrossRef]
- Darlow BA, Hutchinson JL, Simpson JM, Henderson-Smart DJ, Donoghue DA, Evans NJ. Variation in rates of severe retinopathy of prematurity among neonatal intensive care units in the Australian and New Zealand Neonatal Network. Br J Ophthalmol. 2005;89:1592–1596. doi:10.1136/bjo.2005.073650 [CrossRef]
- Karkhaneh R, Mousavi SZ, Riazi-Esfahani M, et al. Incidence and risk factors of retinopathy of prematurity in a tertiary eye hospital in Tehran. Br J Ophthalmol. 2008;92:1446–1449. doi:10.1136/bjo.2008.145136 [CrossRef]
- Lad EM, Nguyen TC, Morton JM, Moshfeghi DM. Retinopathy of prematurity in the United States. Br J Ophthalmol. 2008;92:320–325. doi:10.1136/bjo.2007.126201 [CrossRef]
- 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(2 Pt 1):273.
- Palmer EA. Results of U.S. randomized clinical trial of cryotherapy for ROP (CRYO-ROP). Doc Ophthalmol. 1990;74:245–251. doi:10.1007/BF02482615 [CrossRef]
- Good WV. Final results of the early treatment for retinopathy of prematurity (ETROP) randomized trial. Trans Am Ophthalmol Soc. 2004;102:233–248.
- Repka MX, Palmer EA, Tung B. Involution of retinopathy of prematurity: Cryotherapy for Retinopathy of Prematurity Cooperative Group. Arch Ophthalmol. 2000;118:645–649. doi:10.1001/archopht.118.5.645 [CrossRef]
- Dhaliwal C, Fleck B, Wright E, Graham C, McIntosh N. Incidence of retinopathy of prematurity in Lothian, Scotland, from 1990 to 2004. Arch Dis Fetal Neonatal Ed. 2008;93:F422–F426. doi:10.1136/adc.2007.134791 [CrossRef]
- Gilbert C, Fielder A, Gordilo L, et al. Characteristics of infants with severe retinopathy of prematurity in countries with low, moderate, and high levels of development: implications for screening programs. Pediatrics. 2005;115:e518–e525. doi:10.1542/peds.2004-1180 [CrossRef]
- Shah VA, Yeo CL, Ling YL, Ho LY. Incidence, risk factors of retinopathy of prematurity among very low birth weight infants in Singapore. Ann Acad Med Singapore. 2005;34:169–178.
- Giannantonio C, Papacci P, Cota F, et al. Analysis of risk factors for progression to treatment-requiring ROP in a single neonatal intensive care unit: is the exposure time relevant?J Matern Fetal Neonatal Med. 2012;25:471–477. doi:10.3109/14767058.2011.587056 [CrossRef]
- Fortes Filho JB, Eckert GU, Valiatti FB, Dos Santos PG, da Costa MC, Procianoy RS. The influence of gestational age on the dynamic behavior of other risk factors associated with retinopathy of prematurity (ROP). Graefes Arch Clin Exp Ophthalmol. 2010;248:893–900. doi:10.1007/s00417-009-1248-6 [CrossRef]
- Kumar P, Sankar MJ, Deorari A, et al. Risk factors for severe retinopathy of prematurity in preterm low birth weight neonates. Indian J Pediatr. 2011;78:812–816. doi:10.1007/s12098-011-0363-7 [CrossRef]
- Giapros V, Drougia A, Asproudis I, Theocharis P, Andronikou S. Low gestational age and chronic lung disease are synergistic risk factors for retinopathy of prematurity. Early Hum Dev. 2011;87:653–657. doi:10.1016/j.earlhumdev.2011.05.003 [CrossRef]
Stages of ROP by Gestational Age
|Gestational Age (wk)||Non-ROP (%)||Stage 1 (%)||Stage 2 (%)||Stage 3 (%)||Stage 4 (%)||Total|
|≤ 24||2 (5%)||5 (14%)||19 (51%)||11 (30%)||0||37|
|25 to 26||24 (24%)||10 (10%)||43 (43%)||22 (22%)||1 (1%)||100|
|27 to 28||111 (70%)||16 (10%)||26 (17%)||5 (3%)||0||158|
|29 to 30||76 (86%)||7 (8%)||5 (6%)||0||0||88|
|≥ 31||39 (97%)||0||1 (3%)||0||0||40|
Stages of ROP by Birth Weight
|Birth Weight (g)||Non-ROP||Stage 1 (%)||Stage 2 (%)||Stage 3 (%)||Stage 4 (%)||Total|
|≤ 750||12 (14%)||10 (12%)||38 (44%)||25 (29%)||1 (1%)||86|
|751 to 1,000||64 (50%)||14 (10%)||41 (32%)||10 (8%)||0||129|
|1,001 to 1,250||84 (78%)||11 (10%)||10 (9%)||3 (3%)||0||108|
|1,251 to 1,500||51 (92%)||2 (4%)||2 (4%)||0||0||55|
|≥ 1,500||41 (91%)||1 (2%)||3 (7%)||0||0||45|
Univariate and Multivariate Determinants of ROP
|Risk Factor||ROP Positive||ROP Negative||Unadjusted OR||Adjusted OR|
|Male gender||148||95||0.89 (0.52 to 1.51)||0.86 (0.58 to 1.27)|
|GAa||25.99 (mean)||28.61 (mean)||5.10 (3.68 to 7.04)||2.64 (1.73 to 4.03)|
|BWa||841 (mean)||1,198 (mean)||3.56 (2.74 to 4.63)||1.90 (1.34 to 2.69)|
|Days on ventilation therapya||33.1 (mean)||9.7 (mean)||2.75 (2.11 to 3.58)||1.37 (1.01 to 1.86)|
|Perinatal infection||82/171||83/252||1.88 (1.26 to 2.80)||1.21 (0.69 to 2.14)|
|Transfusions||137/171||125/252||4.09 (2.61 to 6.42)||0.70 (0.36 to 1.36)|
|IVH||90/171||84/252||2.22 (1.49 to 3.31)||1.39 (0.80 to 2.40)|
|PDA||77/171||73/252||2.01 (1.34 to 3.01)||1.31 (0.76 to 2.24)|
|NECa||14/171||4/252||5.95 (1.80 to 17.21)||9.01 (2.06 to 43.47)|