Neonatal Intensive-Care Unit Admission of Infants with Very Low Birth Weight --- 19 States, 2006

Neonatal mortality is disproportionately common among infants with very low birth weight (VLBW) (<1,500 g [3.3 lbs]). In 2006, the mortality rate among infants with VLBW was 240.4 per 1,000 live births (1). Because neonatal intensive care has been shown to reduce mortality among infants with VLBW, current standards call for neonatal intensive-care for all infants with VLBW (2); however, the proportion of infants with VLBW who are admitted to a neonatal intensive care unit (NICU) is not known, nor are the predictors for NICU admission. To estimate the prevalence of admission to NICUs among infants with VLBW and assess factors predicting admission, CDC analyzed birth data from 2006 for 19 states (3). This report summarizes the results of that analysis, which found that overall, 77.3% of infants with VLBW were admitted to NICUs (range: 63.7% in California to 93.4% in North Dakota). Among infants with VLBW born to Hispanic mothers, 71.8% were admitted to NICUs, compared with 79.5% of those with non-Hispanic black mothers and 80.5% of those with non-Hispanic white mothers. Multivariate analysis of the data indicated that preterm delivery, multiple births, and cesarean delivery all were independently associated with greater prevalence of NICU admission among infants with VLBW. Wide variation was observed among states in the prevalence of NICU admission of infants with VLBW; these state data should be assessed further, and barriers to NICU admission should be identified and addressed.

Analyses were limited to live births to U.S. residents that occurred in the 19 states* that adopted the 2003 revised birth certificate because earlier revisions of the birth certificate did not include information on NICU admission. The 19 states represented 49% of U.S. births in 2006, the most recent year for which data were available (3). The revised birth certificate collects information on maternal risk factors, obstetric history, newborn anthropometrics, and NICU admission. Instructions for completing the birth certificate define NICU admission as "admission into a facility or unit staffed and equipped to provide continuous mechanical ventilatory support for the newborn for at least 24 hours" (3). Prevalence estimates with 95% confidence intervals were calculated for NICU admission of infants with VLBW. Overall and pairwise (i.e., non-Hispanic white versus non-Hispanic black and non-Hispanic white versus Hispanic) differences in NICU admission by race/ethnicity were tested using chi-square analyses (with significance at p<0.05). Multivariate log-binomial regression was conducted to assess the independent associations between NICU admission of infants with VLBW and infant gestational age (in weeks, based on the date of last menses) and sex, and mother's parity, race/ethnicity, age group, years of education, plurality, and delivery mode. Generalized estimating equations were used for multivariate models to account for variation among states in NICU admission of VLBW infants. Prevalence ratios and adjusted prevalence ratios (APRs) with 95% confidence intervals were calculated.

Infants weighing <500 g typically are not admitted to an NICU because they are not considered viable (4); therefore, these infants were excluded from analysis. Infants born to Asian/Pacific Islander and American Indian/Alaska Native women (1,252) and to women with unknown race/ethnicity (252) were included in descriptive analyses, but not in multivariate regression analyses. Prevalence estimates also were withheld, because of small numbers, for any state or category with <30 in either the numerator or denominator (0.6% of infants with VLBW).

In 2006, a total of 25,231 infants with VLBW were delivered in the 19-state reporting area; 19,512 (77.3%) of these infants were admitted to NICUs (Table 1). Among the 19 states, the prevalence of NICU admission ranged from 63.7% in California to 93.4% in North Dakota. Overall, a smaller percentage of infants with VLBW born to Hispanic mothers were admitted to NICUs than infants born to non-Hispanic white or black mothers (71.8% compared with 80.5% and 79.5%, respectively). However, racial/ethnic differences in NICU admission varied by state.

Using multivariate analysis, three factors were associated with greater prevalence of NICU admission among infants with VLBW: preterm delivery (<28 weeks, APR = 1.32; 28--31 weeks, APR = 1.36; and 32--36 weeks, APR = 1.27), multiple births (twins, APR = 1.04; triplets or more, APR = 1.08), and cesarean delivery (APR = 1.11) (Table 2). Multivariate analysis found no difference in the prevalence of NICU admission based on infant sex or maternal race/ethnicity, parity, age group, or years of education.

Reported by

WD Barfield, MD, SE Manning, MD, C Kroelinger, PhD, Div of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion; JA Martin, MPH, Div of Vital Statistics, National Center for Health Statistics; DT Barradas, PhD, EIS Officer, CDC

Editorial Note

The findings in this report indicate that, overall in the 19 states sampled, 77.3% of infants with VLBW were admitted to NICUs in 2006, although the percentage of infants admitted to NICUs varied widely by state. Preterm delivery, multiple births, and cesarean delivery were positively associated with VLBW infant NICU admission. Preterm infants and those from multiple births might be perceived as needing more specialized care than term or singleton infants (5), which might explain why they were found more likely to be admitted to an NICU in this analysis. Infants with VLBW delivered by cesarean might have had medical indications that led to choosing cesarean delivery (e.g., congenital cardiac or respiratory abnormalities), and those indications also might have made them more likely to be admitted to an NICU. In addition, multiple births and cesarean deliveries might be more common at facilities with NICUs.

The American Academy of Pediatrics classification system for neonatal care facilities includes three distinct levels of care: level I (basic neonatal care), level II (specialty neonatal care), and level III (subspecialty [i.e., NICU] care) (2). Although all level III neonatal facilities include an NICU, all NICUs do not have a level III designation (certain NICUs offer level II care). Epidemiologic evidence indicates higher survival rates among infants with VLBW born at facilities offering level III care, compared with those born at facilities with lower levels of care or infants transferred after birth (6).

Two national performance measures and objectives have been created to monitor improvements in the availability of neonatal intensive care. The Maternal and Child Health Bureau (MCHB) collects state-level data on the percentage of infants with VLBW delivered at facilities for high-risk deliveries and neonates (performance measure 17) through the Title V Reporting System (7). These data are provided by states and are generally based on birth certificate data. Although some differences exist in the proportion of infants with VLBW receiving specialized care, the findings in this report are generally comparable to MCHB data. However, definitions, criteria, and regulation of hospital-based perinatal centers vary greatly (8); some states identify level II perinatal centers as "facilities for high-risk deliveries and neonates," while others only include level III perinatal centers for this indicator.

In addition to MCHB performance measure 17, Healthy People 2010 objective 16-8 seeks to increase to 90% the percentage of infants with VLBW born at level III hospitals or subspecialty perinatal centers (9). This target is a 23% increase from the baseline of 73% reported in the Title V reporting system during 1996--1997. Current perinatal standards of care recommend admission of all viable infants with VLBW born in a level III facility into the NICU; those standards and the findings in this report should be considered in light of waning efforts in the United States to regionalize perinatal services, which would geographically distribute facilities in such a manner that mothers with high-risk pregnancies will be more likely to give birth in level III facilities.

The findings in this report are subject to at least three limitations. First, these data are representative of 19 states and cannot be generalized to the entire U.S. population. Second, NICU admission is a new variable added to the revised birth certificate. The quality of this new variable has not yet been assessed. For example, these data cannot distinguish between NICU admission at the facility of birth and admission in another facility. Finally, NICU admission might be underreported overall or differentially reported by maternal or infant characteristics, including state of residence and race/ethnicity.

The survival rate is highest when infants with VLBW are born at level III facilities (6). A previous study showed that infants with VLBW who received NICU care, despite being born at a non-level III facility, were 24% more likely to survive than infants who did not receive NIUC care (10); however, another study found that infants with VLBW who are born at a level III facility were 51% more likely to survive than infants born at a lower-level facility (6). Therefore, the ultimate goal of regionalization of perinatal services should be to ensure that mothers with high-risk pregnancies deliver their children in level III facilities with access to NICU services at birth. Understanding barriers to admission of infants with VLBW into NICUs could provide guidance for shaping perinatal care infrastructure and practices within states. Future studies should evaluate the validity of the NICU admission item on the birth certificate and provide suggestions for how data quality might be improved.

References

1. Matthews TJ, MacDorman MF. Infant mortality statistics from the 2006 period linked birth-infant death dataset. Natl Vital Stat Rep 2010;58(17).
2. American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. Guidelines for perinatal care. 6th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2007.
3. Martin JA, Hamilton BE, Sutton PD, et al. Births: final data for 2006. Natl Vital Stat Rep 2009;57(7).
4. Donohue PK, Boss RD, Shepard J, Graham E, Allen MC. Intervention at the border of viability: perspective over a decade. Arch Pediatr Adolesc Med 2009;163:902--6.
5. Lee SK, Penner PL, Cox M. Comparison of the attitudes of health care professionals and parents toward active treatment of infants with VLBW. Pediatrics 1991;88:110--4.
6. Lasswell SM, Barfield WD, Rochat RW, Blackmon L. Perinatal regionalization for very low-birth-weight and very preterm infants: a meta-analysis. JAMA 2010;304:992--1000.
7. Maternal and Child Health Bureau. Title V Information System: national performance measures. Rockville, MD: US Department of Health and Human Services, Health Resources and Services Administration, Maternal and Child Health Bureau; 2010. Available at https://perfdata.hrsa.gov/mchb/tvisreports/measurementdata/measurementdatamenu.aspx. Accessed November 4, 2010.
8. Blackmon LR, Barfield WD, Stark AR. Hospital neonatal services in the United States: variation in definitions, criteria, and regulatory status, 2008. J Perinatol 2009;29:788--94.
9. US Department of Health and Human Services. Maternal, infant, and child health. Objective 16-8: increase the proportion of very low birth weight (VLBW) infants born at level III hospitals or subspecialty perinatal centers. Healthy People 2010 (conference ed, in 2 vols). Washington DC: US Department of Health and Human Services; 2000. Available at http://www.healthypeople.gov/document/html/volume2/16mich.htm. Accessed November 4, 2010.
10. Cifuentes J, Bronstein J, Phibbs CS, Phibbs RH, Schmitt SK, Carlo WA. Mortality in low birth weight infants according to levels of neonatal care at hospital of birth. Pediatrics 2002;109:745--51.

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