A comprehensive longitudinal study by researchers at Vilnius University’s Faculty of Medicine reveals that nearly 80 per cent of all medical diagnoses in children born prematurely are identified before the age of seven, underscoring the urgent need for early, long-term and personalised follow-up care.

Led by Dr Rūta Morkūnienė and Prof. Dr Janina Tutkuvienė, the research traces health trajectories from birth through adolescence and into adulthood, demonstrating that the impact of prematurity extends far beyond the neonatal period. The findings carry global relevance: according to the World Health Organization, an estimated 15 million babies are born preterm each year worldwide. While survival rates have improved significantly, the study challenges the assumption that prematurity-related health issues are limited to infancy, highlighting instead a prolonged and evolving health burden.

Most health risks emerge early in life

One of the most extensive analyses of long-term outcomes in preterm children conducted in Lithuania to date, the study draws on medical records from primary healthcare institutions to map health patterns from birth through adolescence.

Unlike many previous studies, the researchers did not restrict their analysis to conditions traditionally linked to prematurity, such as respiratory or neurological disorders.

“I did not set out to record only diagnoses already described in the literature as typical for preterm children,” explains Dr Morkūnienė, a physician and lecturer at Vilnius University. “I documented everything that each child accumulated over time. What emerged was a very broad spectrum of conditions, often involving multiple organ systems and differing greatly from one child to another.”

The findings show that children born prematurely experience a substantially higher overall disease burden than those born at term. Congenital anomalies, nervous system and mental health disorders, tumours, and diseases of the urinary and reproductive systems were diagnosed three to four times more often than in the general population. Disorders of the immune and blood systems occurred up to ten times more frequently, indicating vulnerabilities that persist well beyond early childhood.

A critical window from birth to age seven

Perhaps the study’s most striking insight relates to the timing of diagnosis.

“More than 45 per cent of all diagnoses are made during the first three years of life,” notes Dr Morkūnienė, “and over 30 per cent more are identified between the ages of three and seven.”

By the age of seven, children born prematurely have already accumulated nearly 80 per cent of all diagnoses they are likely to receive by adulthood. The heaviest disease burden falls on children born with very low birth weight (below 1,500 grams), who not only develop more health conditions overall but also a wider range of them.

“Even children born at the same gestational age and with the same birth weight can follow very different health trajectories,” Dr Morkūnienė adds. “Still, the most premature and smallest infants tend to accumulate both more numerous and more diverse health problems.”

Birth weight outweighs gestational age

A key methodological strength of the study lies in its decision to analyse birth weight and gestational age separately, rather than combining them into a single indicator. This distinction revealed that birth weight is more strongly associated with long-term disease burden than gestational age alone.

Children born with lower birth weight grew more slowly and remained shorter and lighter than their peers into adolescence. While their body mass index (BMI) was initially lower, it began to rise sharply from around the age of nine, eventually surpassing that of children born at term.

“This pattern is increasingly recognised internationally,” explains Prof. Tutkuvienė. “Children born prematurely face a higher risk of long-term metabolic conditions, including obesity and diabetes. By analysing birth weight and prematurity separately, we were able to identify which factor plays a more significant role in specific metabolic processes—one of the key novelties of our research.”

Why population-specific growth standards matter

Beyond individual outcomes, the study highlights a broader challenge in paediatric care: the reliance on outdated or poorly adapted growth standards.

“Until recently, Lithuania did not have head circumference reference values for newborns,” says Dr Morkūnienė. “Height and weight standards were often based on limited or decades-old data.”

Using advanced statistical methods developed by Prof. Tim Cole of the UCL Institute of Child Health, the research team established new, population-specific growth norms for Lithuanian newborns, including preterm infants. While international standards are useful for comparison, the researchers warn that they may misrepresent clinically meaningful thresholds in specific populations, potentially leading to delayed or inaccurate diagnoses.

Survival is not the endpoint

Survival outcomes for preterm infants have improved dramatically. In Lithuania, nine out of ten children born prematurely now survive, placing the country among the global leaders in neonatal care. However, the researchers stress that survival alone should not be viewed as the endpoint.

“Prematurity is not a life sentence,” emphasises Prof. Tutkuvienė. “The human body is remarkably resilient. What truly matters is whether health systems provide timely, personalised and long-term support that allows children to reach their full potential.”

Children born preterm, the researchers argue, require extended, multidisciplinary follow-up, involving not only neonatologists and neurologists but also psychologists, speech therapists, physiotherapists and other specialists who can monitor physical, cognitive and emotional development.

“Early childhood is a period of exceptional developmental flexibility,” says Dr Morkūnienė. “When difficulties are identified early, targeted interventions can make a profound difference. Timely support during these formative years can significantly shape long-term health and wellbeing.”