• Vol. 34 No. 2, 169–178
  • 15 March 2005

Incidence, Risk Factors of Retinopathy of Prematurity Among Very Low Birth Weight Infants in Singapore



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Introduction: To determine the incidence, risk factors and need for surgery for retinopathy of prematurity (ROP) among very-low-birth-weight (VLBW) infants. Materials and Methods: This was a retrospective study of all VLBW infants managed by the department over 14 years, from 1988 to 2001. Preterm infants were examined according to the Royal College of Ophthalmologists’ guidelines, and retinopathy was graded following the International Classification of ROP. All VLBW infants examined for ROP were included and data were retrieved retrospectively and analysed for maternal, medical, obstetric and neonatal risk factors using logistic regression. Results: Of the 564 VLBW infants who fit the screening criteria, ROP was detected in 165 (29.2%) of VLBW infants; of whom 49% of infants had stage 1 disease, 24% were at stage 2, and 27% were at stage 3 or more. Among 45 infants with stage 3 disease or more, treatment was needed in 62.2% (28/45). No ROP was detected in infants greater than 33 weeks of gestation. Only 0.6 % (1/164) of infants greater than 30 weeks of gestational age (GA) needed surgery for ROP. Using birth weight (BW) criteria, stage 3 ROP was noted only in 1% (6/564) of infants with BW >1000 g. Of all ROP requiring surgery, 89% (25/28) of infants were <1000 g as compared to 11% (3/28) who were >1000 g infants. The median age of onset of ROP was 35 weeks (range, 31 to 41) corrected age. By univariate analysis for threshold ROP, preeclampsia, prenatal betamethasone exposure, gestational age, birth weight, 1-minute Apgar score, hyaline membrane disease (HMD), surfactant usage, hypotension, septicaemia, intraventricular haemorrhage duration of supplemental oxygen, ventilation and chronic lung disease were associated with ROP requiring surgery (i.e., threshold ROP, P <0.05). However, using multiple logistic regression analyses for ROP, maternal preeclampsia [odds ratio (OR), 2.52; confidence interval (CI), 1.32 to 4.7], birth weight (OR, 0.99; CI, 0.996 to 0.999), pulmonary haemorrhage (OR, 4.61; CI, 1.04 to 20.4), duration of ventilation (OR, 1.06; CI, 1.04 to 1.08) and duration of continuous positive airway pressure (CPAP) (OR, 1.02; CI, 1.01 to 1.04) were factors predictive of development of threshold ROP. Conclusion: The incidence of ROP among VLBW infants was 29.2%. ROP was strongly associated with smaller, more immature and sicker infants. The median age of onset of ROP was 35 weeks (range, 31 to 40 weeks) postmenstrual age. Infants <30 weeks of GA and/or infant with BW <1000 g are at considerable risk for threshold ROP. The main risk factors for development of threshold ROP by regression analysis are maternal preeclampsia, birth weight, and presence of pulmonary haemorrhage, duration of ventilation and continuous positive pressure ventilation. We suggest that both immaturity and compromised pulmonary function are both important aetiological factors in the development of ROP. Prevention of prematurity, control of preeclampsia, judicious use of ventilation and oxygen therapy are the only promising factors that may reduce the incidence and severity of ROP in this high-risk infant.

Retinopathy of prematurity (ROP) is characterised by abnormal vascular development of retina in premature infants.1 Recent advances in neonatal care have improved the survival rates for premature infants,2 and this has been accompanied by an increase in the incidence of ROP.3-5 ROP is a leading cause of childhood blindness6,7 and accounts for up to 10% of childhood blindness in developed countries.8-10 However, there are few studies on the incidence and risk factors of this important morbidity among very-low-birth-weight (VLBW) infants in Singapore. A high concentration of oxygen therapy was previously thought to be the major contributory factor in the development of ROP.11,12 However, reports have found ROP in cases without oxygen therapy.13 Even after oxygen therapy, not all premature infants develop ROP.13 These evidence suggest that factors other than oxygen play an important role in the development of ROP. Before surfactant became available for clinical use in the neonatal intensive care unit, an incidence of 11% to 60% was reported in the VLBW population.14,15 The last major report of the incidence of ROP was published from the cryotherapy-retinopathy of prematurity (CRYO-ROP) study completed in 1987,16 before surfactant use was approved for treatment of hyaline membrane disease (HMD).

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