Poorer outcomes of all low birth weight groups at age 10: Missouri statewide case-control study
Introduction
Neonatal intensive care has advanced remarkably with neonatologists and developmentalists now routinely running specialized clinics to provide follow-up care. For decades researchers have reported general outcomes for infants below a given gestational age or birth weight for their institutions using population norms as the reference measure. More recently, collaborative networks have examined outcomes from multiple neonatal intensive care units (NICUs). The NICHD research network has allowed researchers to examine follow-up results on large numbers of infants with specific conditions versus infants without those conditions. In these analyses, study site within the network is an important variable. Differences between study sites often emerge, possibly due to treatment differences and patient population differences. The focus of these studies has increasingly been exclusively on extremely low birth weight infants. Vohr's 2014 review of neurodevelopmental outcomes in extremely low birth weight (ELBW) infants concluded “for greater generalizability a population-based study (country, region, state) is preferable to multicenter, which is preferable to a single center study” [1].
Cohort studies of entire populations of low birth weight (LBW) infants have been conducted in other countries [[2], [3], [4], [5], [6], [7], [8], [9]]. Most have not been case-controlled at birth [[2], [3], [4], [5],7,9]; however, in some, control groups were added at time of follow-up study [6]. Studies in Victoria, Australia and Iceland were controlled at birth but only ELBW births were studied [8,10,11]. The EPIPAGE study in France was controlled at birth and studied gestations up to 32 weeks [12], while a controlled-at-birth study in Finland followed-up births weighing <1500 g [13]. In several earlier studies, the desirability of controls was mentioned but cost of obtaining them was prohibitive [2,3]. Given the high-risk profile of LBW infants and NICU graduates, controlling high-risk variables and comparing to normal birth weight (NBW) infants is mandatory to truly assess birth weight-related outcomes. In the absence of NBW infants, researchers have used multiple regression analyses to assess impact of high-risk demographic factors. In many studies maternal education has been a stronger predictor of outcome than medical factors [5,7,14]. In all types of studies, follow-up has been relatively short (2 to 5 years) [2,9,[12], [13], [14]], although longer follow-ups are now appearing [4,5,7,10,11,[15], [16], [17], [18]]. Participants from earlier LBW populations have been studied to adulthood [6,[19], [20], [21]]. A very high proportion of studies have focused exclusively on ELBW infants [1,2,5,8,10,14,17].
A literature search did not uncover a similar comparison follow-up study using statewide data. Hence, the Missouri cohort of all infants born <1500 g during a 16-month period in 1989–1991 and matched as newborns by date of birth, race, maternal age, and area of residence to MLBW and NBW infants, provided a unique opportunity for follow-up investigation to examine developmental outcomes of these children at age 10.
Matching by date of birth, race, maternal age, and area of residence over the full spectrum of possible birth weights in the initial Missouri Maternal and Infant Health Survey (MMIHS) allowed us to test the hypothesis that birth weight (and associated prenatal and postnatal medical problems) was a dominant factor in outcomes at age 10. The objective of this report is to compare in terms of birth weight the children's medical and health history and developmental progress based on their parents'/caregivers' responses to an extensive questionnaire.
Section snippets
Original study design
The preceding Missouri Maternal and Infant Health Survey (MMIHS) involved a statewide population-based, cohort of all births <1500 g using a case-control study design to identify risk factors [22]. Each singleton liveborn infant weighing <1500 g was matched by date of birth (±1 week), mother's race (black vs non-black), age (<20, 20–24, 25+ years), and residence (Kansas City/Jackson County or St. Louis City or County vs the rest of Missouri) to both a MLBW and a NBW infant [23]. Multiple birth
Results
Demographic and other background information about participants in the original MMIHS and the subset participating in the follow-up study at age 10 are shown in Table 1. Similar percentages of children by birth weight group participated in both the original and follow-up studies.
Both the original and follow-up study contained the same proportions of singletons and males. Differences in proportions of parents completing the follow-up questionnaires occurred: in the follow-up study of 10-year-old
Discussion
We believe this is the only statewide, population-based, follow-up study of LBW infants in the United States. We know of no other LBW study that is both case-controlled at birth and represents a population-based cohort study of an area as large and diverse as Missouri with follow-up to age 10. From a national perspective, during the study time period when infants were born (ca. 1990), Missouri was one of the most typical states based on its median ranking on several important socio-demographic
Conclusions
Parent/caregiver reports at age 10 of health, services, and developmental outcomes are compared by birth weight in this follow-up study of a population-based, statewide cohort of VLBW infants and matched at birth to MLBW and NBW infants. Although adverse outcomes occurred much more frequently for ELBW, even MLBW infants had reports of many problems that were significantly greater than in NBW infants. All LBW infants, including MLBW, present significant habilitation and educational challenges
Funding source
This research study was supported by the U.S. National Institute on Deafness and Other Communication Disorders (NIDCD), National Institutes of Health (NIH) research contract number N01-DC-7-2111 with the Missouri Department of Health and Senior Services. Other than the authors, the sponsoring organizations (NIDCD/NIH and Missouri Bureau of Health Data Analysis, Missouri Department of Health and Senior Services) had no role in the design, analysis, and interpretation of the analysis of data; or
Financial disclosure
The authors have no financial relationships relevant to this article to disclose.
Declaration of Competing Interest
None.
Acknowledgements
We thank the children and their parents/caregivers who participated in the original MMIHS and this follow-up study at age 10. We also thank Garland H. Land, MPH, former Director, Division of Health Resources and Center for Health Information Management and Epidemiology, and Mr. Wayne F. Schramm, MA, Bureau of Vital Statistics, Section of Epidemiology for Public Health Practice, Missouri Department of Health and Senior Services, Jefferson City, Missouri for their administrative and scientific
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