European Journal of Cardiovascular Medicine

Birth weight is one of the most powerful predictors of survival, growth, and long-term health in infancy and childhood. The World Health Organization defines low birth weight (LBW) as a birth weight of less than 2500 g irrespective of gestational age, very low birth weight (VLBW) as less than 1500 g, and extremely low birth weight (ELBW) as less than 1000 g ⁽¹⁾. Globally, an estimated 15-20% of all births are low birth weight, with the highest burden concentrated in South Asia and sub-Saharan Africa ^(1,2). In India, the National Family Health Survey and hospital-based data have consistently reported LBW prevalence in the range of 18-30% depending on the population studied ⁽²⁾, making it one of the most pressing public health problems for the country's maternal and child health programmes.

LBW arises from two principal and frequently overlapping mechanisms: preterm birth (delivery before 37 completed weeks of gestation) and intrauterine growth restriction (IUGR), in which the fetus fails to achieve its genetically determined growth potential ⁽³⁾. Maternal factors contributing to LBW include young or advanced maternal age, short stature, low pre-pregnancy weight and poor gestational weight gain, anaemia, hypertensive disorders of pregnancy, multiple gestation, infections, and low socioeconomic status, along with tobacco and alcohol use ^(3,4). VLBW infants are almost always born preterm and represent a physiologically distinct and more vulnerable subgroup, since organ system immaturity compounds the nutritional deficits seen in growth-restricted but term LBW infants ⁽⁴⁾.

The clinical significance of birth weight lies in its strong, graded, inverse relationship with neonatal mortality. Data from large cohort and registry studies show that neonatal mortality rises steeply as birth weight falls below 2500 g, with the steepest rise occurring below 1500 g and below 1000 g ⁽⁵⁾. LBW and prematurity together account for a substantial proportion of all neonatal deaths worldwide, and surviving infants, especially those born VLBW, carry a disproportionate burden of acute neonatal morbidity ^(5,6). Commonly encountered problems in this population include respiratory distress syndrome from surfactant deficiency, hypothermia due to a high surface-area-to-volume ratio and thin subcutaneous fat layer, hypoglycaemia from limited glycogen reserves, feed intolerance and necrotizing enterocolitis, neonatal sepsis due to immature humoral and cellular immunity, hyperbilirubinaemia, intraventricular haemorrhage, and patent ductus arteriosus ^(6,7).

Advances in perinatal and neonatal intensive care, antenatal corticosteroid administration, surfactant therapy, and improved thermoregulation and nutritional strategies have substantially improved survival of VLBW infants over recent decades ^(7,8). However, improved survival has been accompanied by growing recognition that a meaningful proportion of VLBW survivors experience long-term sequelae, including postnatal growth failure, cerebral palsy, cognitive and language delay, visual and hearing impairment, and behavioural problems that become more apparent as the child grows ^(8,9). These long-term outcomes are influenced not only by birth weight and gestational age but also by the severity and duration of neonatal illness, quality of nutrition during hospitalisation and after discharge, and the socioeconomic and caregiving environment to which the infant returns ^(9,10).

Despite the well-established association between birth weight and adverse outcome, there remains a need for region-specific data describing the precise spectrum of neonatal morbidity, mortality rates, and subsequent growth and developmental trajectories of LBW and VLBW infants, since these vary with the level of neonatal care available and the underlying population characteristics ^(10,11). Such data are essential to plan resource allocation, to counsel parents appropriately regarding prognosis, and to design follow-up programmes targeted at the infants who are at greatest risk of long-term disability ^(11,12). The present study was therefore undertaken to determine the pattern of neonatal morbidity, in-hospital mortality, and growth and neurodevelopmental outcomes at one year corrected age among LBW and VLBW infants admitted to a tertiary care neonatal unit, and to compare these outcomes between the two birth weight categories.

Study design and setting: This was a hospital-based prospective observational study conducted in the Neonatal Intensive Care Unit (NICU) and the Pediatric Growth and Development follow-up clinic of a tertiary care teaching hospital, over a period of eighteen months. Ethical clearance was obtained from the Institutional Ethics Committee prior to the commencement of the study, and written informed consent was obtained from the parents or legal guardians of each enrolled infant (11). Study population: All inborn and outborn neonates with a birth weight of less than 2500 g admitted to the NICU during the study period were screened for eligibility. Enrolled infants were classified, in accordance with WHO criteria, into the LBW group (birth weight 1500-2499 g) and the VLBW group (birth weight less than 1500 g) (1). Infants with major congenital malformations incompatible with survival, chromosomal anomalies, and those whose parents declined consent were excluded from the study. Sample size: Based on an anticipated neonatal mortality of approximately 15% in the LBW group and 35% in the VLBW group from previous regional data, with 95% confidence and 80% power, a minimum sample size of 220 infants was calculated; a total of 240 infants were enrolled to allow for attrition during follow-up (2). Data collection: A structured proforma was used to record maternal demographic and obstetric details (age, parity, antenatal care, maternal illness, mode of delivery), neonatal details at birth (gestational age by last menstrual period and/or first-trimester ultrasound, birth weight recorded on an electronic weighing scale to the nearest 10 g, sex, Apgar score, and need for resuscitation), and details of the neonatal course in hospital, including diagnoses such as respiratory distress syndrome, neonatal sepsis (culture-proven or clinical), hyperbilirubinaemia requiring phototherapy, hypoglycaemia, necrotizing enterocolitis, intraventricular haemorrhage (diagnosed by cranial ultrasonography), patent ductus arteriosus, and retinopathy of prematurity where screening was indicated (6,7). Duration of NICU stay and final outcome (discharge, death, or referral) were also recorded. Follow-up protocol: Infants discharged alive were followed up in the pediatric clinic at 6 weeks, 6 months, and 12 months of corrected age (corrected for the degree of prematurity). At each visit, anthropometric measurements (weight, length/height, and head circumference) were taken using standardised, calibrated equipment and plotted on WHO growth charts; growth faltering was defined as a weight-for-age z-score below -2 SD (9). Developmental assessment was performed at 12 months corrected age using the Denver Developmental Screening Test, second edition (DDST-II), which evaluates gross motor, fine motor, language, and personal-social domains; infants with delay in two or more domains were classified as having developmental delay (8,9). Statistical analysis: Data were entered into a Microsoft Excel spreadsheet and analysed using SPSS software. Continuous variables were expressed as mean ± standard deviation and compared between the LBW and VLBW groups using the Student's t-test. Categorical variables were expressed as frequencies and percentages and compared using the Chi-square test or Fisher's exact test, as appropriate. A p-value of less than 0.05 was considered statistically significant throughout the analysis (12).

A total of 240 infants with birth weight less than 2500 g were enrolled, of whom 152 (63.3%) were classified as LBW (1500-2499 g) and 88 (36.7%) as VLBW (<1500 g). The baseline maternal and neonatal characteristics of the two groups are summarised in Table 1.

Mothers of VLBW infants were significantly younger, more likely to have received inadequate antenatal care, more likely to have hypertensive disorders of pregnancy, and more likely to have undergone caesarean delivery than mothers of LBW infants. VLBW infants had a significantly lower mean gestational age and lower 5-minute Apgar score, consistent with the predominantly preterm origin of very low birth weight.

Table 1: Baseline Maternal and Neonatal Characteristics

Table 2: Neonatal Morbidity Profile

VLBW infants experienced significantly higher rates of every major neonatal morbidity assessed, with the largest relative differences seen in necrotizing enterocolitis (6.8-fold), intraventricular haemorrhage (12-fold), and patent ductus arteriosus (7-fold) compared with LBW infants. The mean duration of NICU stay was more than twice as long in the VLBW group, reflecting the greater severity and number of co-existing morbidities in this population.

Table 3: In-Hospital Outcome and Mortality

Overall neonatal mortality was 6.6% in the LBW group compared with 33.0% in the VLBW group, a statistically significant five-fold difference. Sepsis and respiratory failure were the leading causes of death in both groups, while intraventricular haemorrhage contributed to a higher proportion of deaths in VLBW infants than in LBW infants, consistent with the greater immaturity of the germinal matrix vasculature at lower gestational ages.

Table 4: Growth and Neurodevelopmental Outcomes at 12 Months Corrected Age (Survivors)

Among survivors followed up to one year corrected age, growth faltering was nearly three times more common in VLBW infants than in LBW infants, and mean weight at 12 months remained lower in the VLBW group. Developmental delay on DDST-II screening, particularly in the gross motor domain, was significantly more frequent among VLBW survivors, as was the rate of re-hospitalisation during the first year of life. These findings indicate that the survival disadvantage of VLBW infants is compounded by a long-term morbidity burden that persists well beyond the neonatal period.

The present study demonstrates a clear and statistically significant gradient of adverse outcome across the LBW and VLBW categories, with VLBW infants experiencing higher rates of nearly every neonatal morbidity studied, five-fold higher in-hospital mortality, and a substantially greater burden of growth faltering and developmental delay at one year corrected age. These findings are consistent with the well-established literature describing birth weight as a continuous and powerful predictor of neonatal and infant outcome ^(5,6).

The higher rate of respiratory distress syndrome observed in VLBW infants in this study reflects their lower gestational age and consequent surfactant deficiency, a finding mirrored in earlier cohort studies that reported respiratory distress syndrome as the leading cause of early neonatal morbidity in infants born below 32 weeks of gestation ^(6,7). Similarly, the markedly higher incidence of intraventricular haemorrhage and necrotizing enterocolitis in the VLBW group corroborates previous reports linking these complications principally to extreme prematurity rather than to growth restriction alone, since the periventricular germinal matrix and the intestinal mucosal barrier are both particularly vulnerable in infants born before 32 weeks ^(6,8). The finding that maternal hypertensive disorders and inadequate antenatal care were significantly more frequent among mothers of VLBW infants is also in keeping with earlier studies that have identified preeclampsia and poor antenatal care utilisation as important antecedents of very preterm, very low birth weight delivery ^(3,4).

The neonatal mortality rate of 33.0% observed among VLBW infants in this study is comparable to rates reported from other tertiary neonatal units in resource-constrained settings, although it remains considerably higher than the mortality reported from high-income country NICUs with greater access to surfactant therapy, mechanical ventilation, and total parenteral nutrition ^(7,8). This disparity underscores the continuing importance of strengthening perinatal referral systems, ensuring antenatal corticosteroid coverage for anticipated preterm delivery, and improving the availability of essential newborn care equipment in order to narrow the survival gap for the smallest and most immature infants ^(9,10).

Beyond the neonatal period, the present study found that VLBW survivors had significantly higher rates of growth faltering and developmental delay than LBW survivors at one year corrected age, a pattern consistent with longitudinal follow-up studies showing that VLBW and extremely low birth weight infants remain at elevated risk of postnatal growth failure, cerebral palsy, and cognitive impairment well into school age ^(9,11). The predominance of gross motor delay among the developmental abnormalities identified in this cohort is in agreement with previous work suggesting that motor domains are often affected earliest and most consistently in preterm, VLBW children, frequently preceding more subtle cognitive and language deficits that become apparent only at later ages ^(11,12). The higher rate of re-hospitalisation observed among VLBW infants in the first year of life likely reflects both their underlying chronic morbidities, such as bronchopulmonary dysplasia and recurrent respiratory infections, and their generally compromised nutritional and immunological status at the time of discharge ^(10,12).

Taken together, these results reinforce the concept that VLBW infants constitute a distinct high-risk population requiring not only intensive neonatal care to maximise survival, but also structured, longitudinal follow-up extending well beyond hospital discharge, so that growth faltering and developmental delay can be identified and addressed through timely nutritional and early-stimulation interventions ^(11,12). The study's limitations include its single-centre design, which may limit generalisability, and a degree of loss to follow-up that could have led to underestimation of the true burden of long-term morbidity, particularly if infants lost to follow-up were disproportionately those with more severe disability or were lost due to early mortality at home. Larger, multicentric studies with extended follow-up into school age would help to better characterise the full long-term impact of VLBW status on neurodevelopmental and educational outcomes.

This study confirms that birth weight exerts a strong, graded influence on neonatal survival and morbidity, with very low birth weight infants experiencing substantially higher rates of respiratory distress syndrome, sepsis, necrotizing enterocolitis, intraventricular haemorrhage, and in-hospital mortality compared with low birth weight infants. Among survivors, very low birth weight infants also carry a disproportionately higher long-term burden of growth faltering, developmental delay, and re-hospitalisation during the first year of life. These findings highlight the need for comprehensive perinatal strategies that combine high-quality neonatal intensive care with structured post-discharge growth monitoring and developmental surveillance, so that the survival gains achieved in the NICU translate into the best possible long-term outcomes for these vulnerable infants.

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