Follow Up of Prematurely Born Infants
Of the approximately 500,000 infants born in California, 10.5% are delivered at less than 37 weeks gestation and 1.3% are born at less than 32 weeks gestation. With an increasing number of very preterm infants surviving, the number of infants who require specialized follow up care is also increasing. Post-discharge care for the very preterm or very low birth weight infant (less than 1500 grams) includes evaluation of growth, neurodevelopmental status, hearing and vision, as well as the usual immunization and infant medical care. Very low birth weight survivors have a significantly increased need for hospitalization in the first five years of life, with up to 25% of infants with birth weight <1000 grams needing re-hospitalization after discharge.
Follow Up Clinics
Because very preterm infants are at higher risk for medical and neurodevelopmental problems, the babies are followed in high-risk follow up clinics where formal neurologic and cognitive assessments are performed by teams including psychologists, neurologists, pediatric practitioners and social workers. Most high-risk clinics see infants at least three times: at 6 months corrected age, 12-18 months corrected age and 24-36 months corrected age. Because many problems reported in very low birth weight infants do not become apparent until school age, follow up to at least 8-10 years of age is ideal but rarely achieved. Follow up visits serve three distinct functions:
1. Identify infants with potential problems
2. Refer for treatment when appropriate
3. Assess the results of treatment in the intensive care nursery
Growth
The majority of preterm infants have catch-up growth within the first six to nine months of life. In a large Dutch study following premature infant growth, they found that most infants delivered at less than 32 weeks who were appropriate for gestational age reached their target height by 10 years of age but 25% of preterm infants who were small for gestational age (SGA) remained short at 10 years of age. SGA infants who were <10th percentile for height at 5 years of age were more likely to remain short at 10 years of age, although some catch up growth continued. Catch up growth was more likely in SGA infants who had a rapid weight gain in the first three months of life.(1)
Neurodevelopmental Outcome
Many of the recent follow up studies have focused on the extremely low birth weight infant (<1000 grams). Not surprisingly, the incidence of serious adverse outcomes is highest in the lowest gestational age groups. Most appropriate for gestational age infants delivered at >28 weeks gestation have normal neurodevelopmental outcome at 18 month follow up but may have a higher risk of cognitive, learning and behavior disorders including attention deficit hyperactivity disorder. There is some variation in outcome depending on whether it is a single center study, a population study or multicenter study and whether enrollment is by birthweight or gestational age. The NICHD trial prospectively enrolled infants born from 1993 through 1998 with BW <1000 gm at multiple centers. Follow up was at 18 months. Many of the infants in the 27-32 week group were small for gestational age. The data from the cohort born in 1997-1998 are presented below(2):
22-26 wks [1102 (61%) survived to discharge, 84% followed,] mean BW 697 (shown in percent)
Any cerebral palsy (CP): 18.1%
Moderate-severe CP: 10.4%
Bayley-MDI <70: 37.2%
PDI <70: 26.0%
Blind (bilateral): 1.0%
Neurodevelopmentally impaired: 44.6%
27-32 wks [633 (86%) survived to discharged, 82% followed] mean BW 851 (shown in percent)
Any cerebral palsy (CP): 11.3%
Moderate-severe CP: 6.3%
Bayley-MDI <70: 22.8%
PDI <70: 16.9%
Blind (bilateral): 0.4%
Neurodevelopmentally impaired: 27.8%
Factors associated with worse outcomes include lower gestational age, intrauterine growth restriction, intraventricular hemorrhage, prolonged mechanical ventilation, use of post-natal steroids and poor postnatal growth. Follow up studies at school age have shown an increased risk of learning and behavioral problems with 30% of infants less than 1500 grams and 50% of infants <1000 grams requiring special services in school.
In spite of these concerning findings from the U.S. study, a twenty year follow up of extremely low birth weight infants born in Canada found that at 23 years of age, the extremely low birth weight infants compared favorably with term infants in rate of high school graduation (82 vs. 87%), post secondary education (32 vs. 33%), permanent employment (48 vs. 57%) and independent living (42 vs. 53%).(3) Other studies have found that cognitive outcome is more closely associated with maternal education level than gestational age.(4)
Vision
The most recent recommendation is that all infants <32 weeks gestation and/or <1500 grams and any infant >32 weeks with risk factors during their hospitalization be screened for retinopathy of prematurity (ROP). Infants who have any degree of ROP are at increased risk for myopia. Preterm infants have a higher risk for strabismus, severe myopia and amblyopia. For infants with ROP, post discharge examinations are based on the ophthalmology recommendations. All infants <32 weeks, regardless of ROP status, should be evaluated by an ophthalmologist at one year of age.
Hearing
Hearing loss is increased ten fold in infants <32 weeks gestation compared to infants delivered at term. In general, most preterm infants are screened with brainstem auditory responses prior to discharge. Repeat screening is performed in all infants who refer on the initial screening. However, some preterm infants who pass the initial screening are found to have sensorineural hearing loss not detected by the initial screen.
All infants delivered at <32 weeks gestation or <1500 grams birth weight are eligible for follow up testing and interventional services. They are at significantly increased risk of medical problems requiring hospitalization and cognitive, neurodevelopmental and neurosensory disability that may be ameliorated by early identification and treatment.
References
1. Knops N.B, Sneeux, K et al. Catch-up growth to ten years of age in children born very pretermor with very low birth weight. BMC Pediatrics 5:26, 2005
2. Vohr, BR, Wright, LL et al. Neurodevelopmental Outcomes of Extremely Low Birth Weight Infants <32 weeks’ gestation between 1993 and 1998. Pediatrics 116: 635, 2005.
3. Saigal S, Stoskopf B, et al. Transition of extremely low-birth-weight infants from adolescence to young adulthood: comparison with normal birth weight controls. JAMA 295: 667, 2006.
4. Gross SJ, Mettleman BB et al. Impact of family structure and stability on academic outcome in preterm children at 10 years of age. J Pediatr 138: 169, 2001.
This information provided by Jerry Mednick, M.D., Whitney Follow Up Clinic, and Kathleen Lewis, M.D., Newborn Intensive Care Unit, California Pacific Medical Center's Department of Pediatrics.