Perinatal factors associated with retinopathy of prematurity

Retinopathy of prematurity: contribution of inflammatory and genetic factors

Retinopathy of prematurity (ROP) is a retinal vasoproliferative disorder that represents an important cause of childhood visual impairment and blindness. Although oxidative stress has long been implicated in ROP etiology, other prenatal and perinatal factors are also involved. This review focuses on current research involving inflammation and genetic factors in the pathogenesis of ROP. Increasing evidence suggests that perinatal inflammation or infection contributes to ROP pathogenesis. Cytokines and chemokines with a fundamental role in inflammatory responses and that significantly contributing to angiogenesis are analyzed. Microglia cells, the retinal-resident macrophages, are crucial for retinal homeostasis, however, under sustained pathological stimuli release exaggerated amounts of inflammatory mediators and can promote pathological neovascularization. Current modulation of angiogenic cytokines, such as treatment with antibodies to vascular endothelial growth factor (anti-VEGF), has shown efficacy in the treatment of ocular neovascularization; however, some patients are refractory to anti-VEGF agents, suggesting that other angiogenic or anti-angiogenic cytokines need to be identified. Much evidence suggests that genetic factors contribute to the phenotypic variability of ROP. Several studies have implicated the involvement of candidate genes from different signaling pathways in the development of ROP. However, a genetic component with a major impact on ROP has not yet been discovered. Most studies have limitations and did not replicate results. Future research involving bioinformatics, genomics, and proteomics may contribute to finding more genes associated with ROP and may allow discovering better solutions in the management and treatment of ROP.

Retinopathy of prematurity: a review of risk factors and their clinical significance

Retinopathy of prematurity (ROP) is a retinal vasoproliferative disease that affects premature infants. Despite improvements in neonatal care and management guidelines, ROP remains a leading cause of childhood blindness worldwide. Current screening guidelines are primarily based on two risk factors: birth weight and gestational age; however, many investigators have suggested other risk factors, including maternal factors, prenatal and perinatal factors, demographics, medical interventions, comorbidities of prematurity, nutrition, and genetic factors. We review the existing literature addressing various possible ROP risk factors. Although there have been contradictory reports, and the risk may vary between different populations, understanding ROP risk factors is essential to develop predictive models, to gain insights into pathophysiology of retinal vascular diseases and diseases of prematurity, and to determine future directions in management of and research in ROP.

Neonatal Risk Factors for Treatment-Demanding Retinopathy of Prematurity: A Danish National Study

PURPOSE

One goal of the study was to identify "new" statistically independent risk factors for treatment-demanding retinopathy of prematurity (ROP). Another goal was to evaluate whether any new risk factors could explain the increase in the incidence of treatment-demanding ROP over time in Denmark.

DESIGN

A retrospective, register-based cohort study.

PARTICIPANTS

The study included premature infants (n = 6490) born in Denmark from 1997 to 2008.

METHODS

The study sample and the 31 candidate risk factors were identified in 3 national registers. Data were linked through a unique civil registration number. Each of the 31 candidate risk factors were evaluated in univariate analyses, while adjusted for known risk factors (i.e., gestational age [GA] at delivery, small for gestational age [SGA], multiple births, and male sex). Significant outcomes were analyzed thereafter in a backward selection multiple logistic regression model.

MAIN OUTCOME MEASURES

Treatment-demanding ROP and its associations to candidate risk factors.

RESULTS

Mechanical ventilation (odds ratio [OR], 2.84; 95% confidence interval [CI], 1.99-4.08; P < 0.01) and blood transfusion (OR, 1.97; 95% CI, 1.20-3.14; P = 0.01) were the only new statistically independent risk factors, in addition to GA at delivery, SGA, multiple births, and male sex. Modification in these prognostic factors for ROP did not cause an increase in treatment-demanding ROP.

CONCLUSIONS

In a large study population, blood transfusion and mechanical ventilation were the only new statistically independent risk factors to predict the development of treatment-demanding ROP. Modification in the neonatal treatment with mechanical ventilation or blood transfusion did not cause the observed increase in the incidence of preterm infants with treatment-demanding ROP during a recent birth period (2003-2008).

Incidence of retinopathy of prematurity in southwestern China and analysis of risk factors

Background

The aim of this study was to screen for retinopathy of prematurity (ROP) in southwestern China and understand the prevalence and risk factors of ROP, which may provide evidence useful in the prevention and treatment of ROP.

Material/Methods

1864 preterm infants (gestational age of <37 weeks and birth weight of ≤2500 g) underwent ROP screening from January 2009 to November 2012 in Southwest China. The medical information of infants during perinatal period was reviewed, and risk factors of ROP were determined. A total of 1614 infants were recruited for final analysis.

Results

Incidence of ROP was 12.8%. The first, second, third, and fourth stage of ROP was found in 64.6%, 29.6%, 3.4%, and 0.5% of infants, respectively. No fifth stage of ROP was observed. In addition, 7.7% of infants required surgical intervention. In our Department of Neonatology, the incidence of ROP was 20.0%, which was significantly higher than in non-hospitalized patients (9.9%). The incidence of ROP remained unchanged over the years. Independent risk factors of ROP included low birth weight (p=0.049), low gestational age (p=0.008), days of oxygen supplementation (p=0.008), and myocardial injury after birth (p=0.001).

Conclusions

The prevalence of ROP in preterm infants is relatively high in Southwest China, and low birth weight, low gestational age, days of oxygen supplementation, and myocardial injury after birth are independent risk factors for ROP.

Retinopathy of prematurity in very low birth weight infants and the potential protective role of indomethacin

BACKGROUND AND OBJECTIVE

To describe clinical features of very low birth weight (VLBW) infants and examine the effect of indomethacin on the incidence of retinopathy of prematurity (ROP).

PATIENTS AND METHODS

Medical records of all VLBW infants over a 4-year period were reviewed. Data regarding systemic and ophthalmic examinations were analyzed.

RESULTS

Forty-seven infants with ROP were evaluated. Most infants had bilateral stage 1 or 2 disease extending 5 clock hours. Infants with ROP had younger mean gestational age, had lower gestational weight, and demonstrated higher incidence of diseases of prematurity. These infants were exposed to increased doses of surfactant and higher oxygen concentration for a prolonged duration given their immature pulmonary status. Independent predictors of ROP susceptibility also included length of hospitalization and Apgar score at 5 minutes. Patent ductus arteriosus was more common among infants with ROP. Approximately half of the infants who received one or two doses of indomethacin had ROP, but the ROP rate was decreased in infants who received three doses.

CONCLUSION

Premature infants with younger gestational age, lower gestational weight, and severe morbidities were found to have an increased prevalence of ROP. Indomethacin treatment for patent ductus arteriosus may have a protective role in the development of severe ROP.

Retinopathy of prematurity

This article briefly reviews the history of ROP followed by a discussion of the pathogenesis of this complex disorder. We describe the International Classification System for ROP and identify risk factors and screening recommendations. Finally, we discuss some of the measures that have been used in an attempt to both prevent and treat ROP.

Wide-field digital imaging based telemedicine for screening for acute retinopathy of prematurity (ROP). Six-year results of a multicentre field study

Objective

To report on a 6-year experience with wide-field digital imaging based telemedicine (WFDI telemedicine) to reduce the risk for blindness from retinopathy of prematurity (ROP).

Methods

Wide-angle digital fundus cameras (RetCam 120, Massie Lab, Pleasanton, CA, USA) were installed in five neonatal intensive care units (NICUs) in Germany. All prematures at risk were screened with WFDI, and the local ophthalmologists were asked to continue binocular indirect ophthalmoscopy (BIO) according to the German guidelines. Image data were coded and transferred to the Reading Centre in Regensburg. Image evaluation and additional BIO of infants with suspected treatment-requiring ROP (STR-ROP i.e. threshold ROP zone II, prethreshold ROP zone I (type-1 ROP according to ETROP), and ROP possibly requiring treatment but not reliably classifiable from the images) were performed by paediatric ophthalmologists at the Reading Centre. ROP was classified following ICROP, ETROP, and revised ICROP criteria. Outcome measures were incidence of clinically relevant ROP (CR-ROP, i.e. any ROP up to mid-peripheral zone III, ≤ stage 3+), sensitivity to detect STR-ROP, and positive predictive value to detect treatment-requiring ROP (TR-ROP).

Results

In total, 1,222 prematures at risk were screened (mean BW 1395 g, SD ±507 g; mean GA 30 wks, SD ±3 wks). The overall incidence of CR-ROP was 27.6% (71.8% mild = stage 1 to 3 without plus disease, 15.7% prethreshold = type-1 ROP according to ETROP, 12.5% threshold according to ICROP). Zone I disease was present in 3.3%, zone II disease in 76.5%, and zone III disease in 20.2%. According to ETROP, 95 infants were type-1 or type-2 ROP; 67.4% type-1 ROP, and 32.6% type-2 ROP. Of all 1,222 infants, 3.5% received treatment. Following ETROP (not applied in the study), 5.3% would have been treated. The sensitivity for detecting STR-ROP was 100%, and the positive predictive value for TR-ROP 82.4% (28/34) at the time of the first referral (28 infants, ≤ stage 3+ in zone I or II).

Conclusion

All TR-ROP was detected in time, showing the potential of our telemedical screening program. The overall incidence of CR-ROP was comparable to ROP incidences reported in other West European countries.

Screening for retinopathy of prematurity in a tertiary care newborn unit in Turkey: frequency, outcomes, and risk factor analysis

PURPOSE

To report the frequency, risk factors, and outcomes of screening for retinopathy of prematurity (ROP).

METHODS

Data of neonates with a gestational age of 34 weeks or less were analyzed and the predictors on the development of ROP were determined by using logistic regression analysis.

RESULTS

Of the 318 neonates, the frequency of ROP was 37.1% for any stage and 7.2% for stage 3 or greater. Treatment was needed in 16.1% of neonates with ROP. No treatment was required in neonates with a gestational age of greater than 32 weeks. Oxygen therapy, sepsis, gestational age of 32 weeks or less, and birth weight of less than 1,250 g were determined as the independent risk factors.

CONCLUSIONS

Although frequency of ROP in Turkey is similar to that in the United States, the rate of severe ROP necessitating treatment seems to be higher in Turkey. Neonates with a gestational age of 32 weeks or less, a birth weight of less than 1,250 g, sepsis, and oxygen therapy may have a greater risk of developing ROP and screening should be intensified in the presence of these risk factors.

Risk factors in the development of mild and severe retinopathy of prematurity

PURPOSE

To evaluate the risk factors in the development of mild and severe retinopathy of prematurity (ROP).

METHODS

All infants (n = 88) screened for ROP at a neonatal intensive care unit over a 2-year period with gestational age <or=34 weeks and follow-up of 43 weeks postconception were included. The findings were classified in accordance with the International Classification of Retinopathy of Prematurity. The study group was classified into three subgroups: group A included patients without retinopathy; group B included patients with stage 1 or 2 (mild-ROP); and group C included patients who progressed to moderate or severe stage 3 (severe-ROP) and were treated. A retrospective review of records was performed and statistical analysis of eight possible risk factors for ROP was evaluated by using logistic regression.

RESULTS

Logistic regression analysis showed birth weight (BW) (p=0.019) and respiratory distress syndrome (p = 0.029) as independent significant risk factors for the development of stage 1 and 2 ROP, with BW (p < 0.0001) as an independent significant risk factor for the progression to stage 3 ROP. Total volume of blood transfusion and duration of artificial ventilation were also found to be risk factors with high rates of stage 3 ROP. In group C, BW <or=1000 g (p = 0.0002) and gestational age <or=28 weeks (p < 0.0001) were significant risk factors associated with higher rates of ROP.

CONCLUSIONS

This study showed BW and respiratory distress syndrome as independent risk factors in the development of mild ROP and BW in the development of severe ROP.

Association between higher cumulative doses of recombinant erythropoietin and risk for retinopathy of prematurity

BACKGROUND

Retinopathy of prematurity is a complication of premature birth that varies in its severity. The incidence and severity of retinopathy of prematurity at our perinatal center in a regional referral hospital changed substantially during 1995 to 1998 and presented us with an opportunity to examine whether there was a protective effect on risk of retinopathy associated with exposure to recombinant erythropoietin.

METHODS

We undertook a retrospective cohort study. From January 1995 through December 1998, charts of infants weighing<1500 g, who were 30 weeks' gestation or less, and who were admitted and survived to the first eye examination at 6 weeks were reviewed. Primary and secondary risk factors were recorded from the first 6 weeks of life. Of the eligible infants, 327 of 390 (84%) had complete records and retinal examinations. The probability for progression of retinopathy was estimated by logistic regression multivariate analysis using the continuation-ratio model.

RESULTS

The overall incidence of retinopathy of prematurity was 36%. Recombinant erythropoietin exposure, as total 6-week dose, was independently associated with an increased risk for progression of retinopathy, OR=1.27 per 500 units/kg (95%CI=1.04, 1.55, P=0.02). Postnatal day of recombinant erythropoietin initiation also was associated with retinopathy risk but did not reach conventional statistical significance, OR=1.07 (CI=1.00, 1.14, P=0.07).

CONCLUSIONS

These findings identify an association between cumulative recombinant erythropoietin exposure, used to reduce blood transfusions in premature infants, and an increased risk for retinopathy of prematurity. The nonhematopoietic properties of erythropoietin may account for the above findings, however further evaluation with confirmation is required.

Postnatal risk factors of retinopathy of prematurity

To investigate the postnatal risk factors of retinopathy of prematurity (ROP), we analysed demographic and clinical data abstracted from the medical records of 425 premature babies who were examined for ROP between January 1994 and December 1998 at Asan Medical Centre, Seoul, Korea. ROP developed in 20.7% of the cases studied. A gestational age (GA) of < or = 28 weeks and birthweight (BW) of < or = 1000 g were the most significant risk factors. Ventilator care for > or = 48 h, apnoea, and use of surfactant independently increased the incidence of ROP. Furthermore, frequent apnoeic attacks increased the progression of pre-threshold ROP to threshold ROP. Therefore, as well as GA and BW, apnoea, prolonged use of a ventilator, and surfactant therapy are significant independent risk factors for ROP. In addition, apnoea may not only increase the risk of developing ROP, but may also worsen pre-existing ROP.

Visual impairment in children born prematurely from 1972 through 1989

PURPOSE

To investigate the incidence and causes of visual impairment in children born prematurely in Finland from 1972 through 1989, and to determine what conditions and factors were associated with its occurrence.

DESIGN

Retrospective, cross-sectional study.

SUBJECTS

All visually impaired individuals from 0 to 17 years of age who had been born at fewer than 37 gestational weeks in Finland from 1972 through 1989 for whom records were available in the Finnish Register of Visual Impairment were eligible for this study.

METHODS

Data in the Finnish Register of Visual Impairment relating to 556 children were supplemented with data from hospital records, and from the Register of Births, the Register of Congenital Malformations, the Finnish Care Register, and the Finnish Cancer Register. Data relating to causes associated with visual impairment in particular were collected. Data relating to the children born prematurely were compared with data relating to children born at full term. The chi-square test (Mantel-Haenszel), the Mann-Whitney U test, Fisher exact test, and stepwise logistic regression analysis were used in statistical analysis of the data.

MAIN OUTCOME MEASURES

Visual acuity, ophthalmologic diagnoses, associated systemic disease, multiple handicap, gestational age, birth weight, 5-minute Apgar scores, and prenatal, perinatal, and infantile or juvenile disorders or disease and treatment.

RESULTS

One hundred twenty-five of the 556 visually impaired children (23%; 11/100000 children less than 18 years of age) had been born preterm. Retinopathy of prematurity, optic atrophy, and cerebral amblyopia were the main diagnoses associated with visual impairment (in 46%, 28%, and 12% of cases, respectively). Sixty-six percent of those born prematurely with visual impairment were also affected by other handicaps (mental, motor, auditory), 54% by cerebral palsy and 36% by epilepsy. Eighty-eight of the 125 children (70%) born preterm with visual impairment were blind. Very low birth weight (<1500 g), young gestational age (fewer than 30 weeks), prenatal infection, hyperbilirubinemia, respiratory disorders, asphyxia, and lengthy mechanical ventilation were associated with an increased risk of visual impairment.

CONCLUSIONS

Premature birth was a major risk factor of severe visual impairment and blindness in childhood. The visual impairment often was accompanied by cerebral palsy, epilepsy, and other motor and mental handicaps. Retinopathy of prematurity, optic atrophy, and cerebral amblyopia were the main diagnoses associated with visual impairment. During the 18 years covered by the study, the increasing incidence of survival of infants born weighing fewer than 1500 g was associated with increasing incidence of blindness.

Ophthalmologic follow-up of premature twins and triplets

PURPOSE

To assess the influence of multiple gestation on the visual apparatus and on the general state of health of premature infants and to investigate the condition of the twin or triplet with the lowest birth weight compared to multiple gestation siblings.

METHODS

Seventy-seven premature twins or triplets (8 to 54 months of age) were monitored at the Verona University Ophthalmology Department from November 1995 to November 1999. In another 12 subjects (younger than 8 months), only the neonatal disease records were examined; these subjects were excluded from the ophthalmologic follow-up because they were too young to be tested reliably. The study sample was compared with 120 premature singletons monitored from January 1996 to March 1998. Visual acuity, ocular motility, strabismus, refraction defects, dioptric media, and fundus oculi were assessed.

RESULTS

The incidence of retinopathy of prematurity, refraction defects, or strabismus was not significantly different between premature twins or triplets and premature singletons. The twin or triplet with the lowest birth weight was more frequently affected by eye morbidity and the diseases typical of prematurity. This difference, however, was not statistically significant.

CONCLUSIONS

Premature infants are at a disadvantage compared to those born at term, irrespective of multiple birth status; multiple gestation adds no risk beyond that due to prematurity.

Physical growth and retinopathy in preterm infants: involvement of IGF-I and GH

GH and IGF-I are important for physical growth. We measured serum levels of these factors in preterm infants. The study population (n = 81) was divided into three groups according to the gestational age. We evaluated differences in serum GH and IGF-I levels among groups with regard to physical growth and development of retinopathy of prematurity. Serum GH levels in extremely preterm infants born at <28 wk of gestational age were significantly higher than levels in those born between 28 and 34 wk at 1 and 2 mo of age. In contrast, serum IGF-I levels in extremely preterm infants remained low, whereas those in the other two groups gradually increased. Evaluation of the effects of GH and IGF-I on physical growth in very low birth weight infants (<1500 g) showed that IGF-I concentrations were positively related to physical growth for several months after birth, whereas no relationship was observed between GH and physical growth. Multivariate analysis demonstrated that high GH concentration at 1 mo of age was significantly associated with development of severe retinopathy of prematurity. In conclusion, persistent low serum IGF-I levels may explain the slow physical growth during neonatal life, and exposure of high GH may cause, at least in part, severe retinopathy of prematurity in preterm infants.

Retinopathy of prematurity: causation

The incidence of ROP is birth weight dependent and restricting therapeutic oxygen levels has dramatically reduced the incidence of ROP in infants of birth weight >1000 g. However, the incidence of ROP has remained high in very low birth weight (VLBW) infants and this appears to be related to these babies being more ill. Several risk factors have been identified in this group, however oxygen variability, rather than high levels, has been correlated with severity of disease in recent clinical and animal studies. Difficulties in defining 'normal' oxygen in this group has meant the optimal range of oxygen therapy has not yet been defined. Clinical studies are now underway using even lower oxygen therapy ranges. The impact this may have on ROP, neurological and respiratory outcomes will require further study.

Retinopathy of prematurity in multiple-gestation pregnancies

PURPOSE

To determine differences in incidence of retinopathy of prematurity between neonates of multiple-gestation and single-gestation pregnancies and to analyze differences in severity of retinopathy of prematurity among siblings of multiple-gestation pregnancies.

METHODS

We reviewed the records of 149 neonates of multiple-gestation pregnancies and 691 single-gestation neonates screened for retinopathy of prematurity at one hospital from January 1, 1992, through December 31, 1995. The peak stage of retinopathy of prematurity was recorded for all infants. The multiple-gestation infants were then separated into concordant and discordant retinopathy of prematurity groups, with discordance defined as a difference of at least 2 stages of retinopathy of prematurity between siblings. Between siblings with discordant retinopathy of prematurity, multiple factors were compared.

RESULTS

Retinopathy of prematurity was present in 69 (46%) of the multiple-gestation neonates. Retinopathy of prematurity was present in 312 (45%) of single-birth neonates. The percentage of multiple-gestation neonates with stages 1, 2, or 3 (prethreshold) or threshold retinopathy of prematurity was similar to that of single-gestation neonates. Stage 4 or 5 retinopathy of prematurity did not occur in either group.

CONCLUSIONS

There was no significant difference in stage of retinopathy of prematurity between infants of single-gestation pregnancies vs those of multiple-gestation pregnancies. The majority (84%) of infants of multiple-gestation pregnancies had concordant retinopathy of prematurity. In those infants with discordant disease, zygosity and postgestational factors other than lowest serum glucose were not related to severity of retinopathy of prematurity.

Incidence of retinopathy of prematurity (ROP) in the western part of Norway. A population-based retrospective study

We have investigated the incidence of retinopathy of prematurity (ROP) among premature infants with birth weight less than 1500 g in two Norwegian counties during the years 1989-1993. Two hundred and seven out of 244 such infants (84.8%) were examined at the neonatal intensive care unit; 66 of those examined (31.9%) had a birth weight below 1000 g. ROP was found in 21 patients (10.1%), and stage 3 disease was present in 7 (3.4%). No patient had more advanced ROP than stage 3. Assuming that no cases of stage 3 ROP were missed among the total of 244 children, the incidence of stage 3 disease was 2.9%. The frequency of ROP in this study is compared to that of other population-based studies in the Nordic countries, and incidence differences are discussed.

Control of cerebral and ocular blood flow autoregulation in neonates

Several factors have been implicated in the regulation of cerebral and ocular vasomotor tone in the newborn: the interrelationship between prostanoids, NO, and other vasoactive mediators remains a subject of interest and active investigation. Pharmacologic modulation may provide new treatment modalities for diseases of the newborn that are mostly hemodynamic and vascular in nature.

Comparison of morbidities in very low birthweight and normal birthweight infants during the first year of life in a developing country

OBJECTIVE

To compare the morbidities in the very low birthweight (VLBW; < 1500 g) and normal birthweight (NBW; > or = 2500 g) Malaysian infants during the first year of life.

METHODOLOGY

Prospective observational cohort study of consecutive surviving VLBW infants and randomly sampled NBW infants born in the Kuala Lumpur Maternity Hospital between 1 December 1989 and 31 December 1992. Infants were followed up regularly during the first year of life, after correction for prematurity.

RESULTS

Compared with NBW infants (n = 106), VLBW infants (n = 127) had significantly higher risk of failure to thrive (odds ratio [OR] = 8.0, 95% confidence intervals [CI]: 1.1 to 354.3), wheezing (OR = 3.7, 95% CI: 1.6 to 9.3), rehospitalization (OR = 2.3, 95% CI: 1.1 to 5.0), cerebral palsy (OR = 8.6, 95% CI: 2.0 to 77.6), neurosensory hearing loss (OR = 12.0, 95% CI: 1.7 to 513.6) and visual loss (7.9 vs 0%, P = 0.002). The mean mental developmental index (MDI) and mean psychomotor developmental index (PDI) at 1 year of age were significantly lower among VLBW infants (MDI 99 [SD = 28], PDI 89 [SD = 25]) than NBW infants (MDI 106 [SD = 18], PDI 101 [SD = 18]) (95% CI for difference between means being MDI: -14.1 to -1.7; and PDI: -17.6 to -6.0). Logistic regression analysis showed that among VLBW infants: (i) male sex, Malay ethnicity and bronchopulmonary dysplasia were significant risk factors associated with wheezing; (ii) longer duration of oxygen therapy during the neonatal period, seizures after the post-neonatal period and wheezing were significant risk factors associated with rehospitalization; and (iii) longer duration of oxygen therapy during the neonatal period was a significant risk factor associated with adverse neurodevelopmental outcome during the first year of life.

CONCLUSIONS

Compared with NBW infants, VLBW Malaysian infants had significantly higher risks of physical and neuro-developmental morbidities.

Risk factors associated with retinopathy of prematurity (ROP) in northern Jutland, Denmark 1990-1993

This population-based, historical, follow-up study analysed possible risk factors for retinopathy of prematurity (ROP) and resulting visual impairment in newborns over a period of 3 1/2 years in the County of Northern Jutland, Denmark. The study subjects were 141 infants with birth weight < or = 1500 grams and gestational age < 35 completed weeks who survived to a first eye examination at 5 weeks. The incidence of ROP (all stages) was 18%, and the frequency of severe visual impairment from ROP was 14/100,000 live births. A logistic regression analysis identified low gestational age, multiple births, continuous oxygen treatment, and male sex as risk factors for ROP. The main factor in the prevention of ROP is to prevent preterm births.