Modern and innovative methods of intensive care have reduced the chances of infant mortality among unhealthy newborns and preemies. The earlier the gestational age, the higher are the chances of infant mortality. Various maternal and socio-economic conditions constitute important causal factors in unhealthy preterm deliveries. Persons born pre-term tend to go through negative long-term repercussions which can impact their quality of life. About 26.2 billion dollars has been reported as the annual societal economic burden associated with pre-term birth in the United States in 2005. Currently, methods of diagnosis and treatment of pre-term labour are inadequate and little is known about the prevention of such births.
It was hypothesized that stress levels are higher in young adults born preterm than young adults born at term and the objective behind the research was to find whether there exists a higher level of stress in young adults born pre-term compared to young adults born at term.
A sample of 60 young adults between the ages of 20 to 25 was taken-30 young adults born pre-term and 30 young adults born at term were selected. Through the scores obtained on a standardised questionnaire, it was found that young adults born preterm are at a somewhat higher risk of showing stress or rather, are stressed, than young adults who were born full-term.
Stress levels in various groups of individuals and individual responses to various stressors have been the centre of attention in health research. Stress has been defined based on stressors in terms of environmental conditions and also on the basis of individual reactions to stress. An individual's reaction encompasses perception processing and emotional response. Studies indicate that environmental conditions and emotional response together qualify as the factors that best represent the experience of stress. (Fliege, 2005).
Modern methods of intensive care have been introduced in the past few decades. These methods have increased the survival rates in infants born pre-term with very low birthweight (VLBW) and also decreased the chances of neurological impairment and mortality in these infants. However, various long-term studies in VLBW infants indicate problems in mental health, psychological development and social and academic competencies during childhood and adolescence. These problems may persist into young adulthood. Reports of low IQ and problems concerning academics in young adults have also been a matter of concern. However, any information based on the mental health of the VLBW subjects as compared with regard to other abilities is inconsistent and seldom found. It has also been observed that several studies have shown controversial results and this has further complicated the problem. Cooke and Bjerajer did not find any differences between pre-term and term subjects in areas of overall mental health and well being. Conversely, Hack and his colleagues observed attention problems, withdrawn behaviour and higher levels of parent-reported thought in 20-year old VLBW subjects. Several studies also suggest that intrauterine growth patterns may be responsible for being born small for gestational age (SGA) or appropriate for gestational age (AGA). This in turn may modify the developmental outcomes of VLBW infants.
The earlier the gestational age during the baby's birth, the more likely are the chances of death or infant mortality, whereas other preemies who survive suffer on and go through a series of disturbing experiences. However, these findings were in disagreement with other studies on mental health outcomes of VLBW adults as no study indicated that VLBW born AGA would do better than SGA or term born adults. Also, data on mental health outcomes during development till adulthood was lacking, the study could not identify continuity and change in behaviour in the VLBW and control groups over time. However, the findings match some of earlier findings that suggest that the developmental outcomes of VLBW infants may be adjusted by AGA and SGA status. (Raikkonen, 2008).
The benefits of listening to music are numerous, besides relaxation there are further aspects wherein its powers can be applied.
Music's relaxing effects can be seen on newborns as well, and its impact on preemies is reasonably good. When Fifty-two preterm and low-weight babies were taken as subjects, and were split into control and experimental groups, the control group received normal auditory stimulation while the experimental group received musical stimulation from a tape containing vocal music, including children's music and lullabies, as well as the normal auditory stimulation.
It was found that the experimental group had a comparatively shorter stay in both the newborn intensive care unit and the hospital itself as well as less weight loss than the control group. Resulting weight gain was also reduced in the experimental group. Also, the experimental group's formula intake was much lower than the control group, however their caloric intake wasn't reduced, and it remained the same. (Caine, 1992)
Although pre-term birth has been associated with difficulties and incompetencies in several areas like academics, psychiatric morbidity, cognitive ability and self-esteem, only a few studies have examined the effects of pre-term birth on adult personality. Prematurely born children, out of school and in adulthood have hardly been studied. Adolescence and young adulthood is the period during which an individual adapts to the surrounding changes while acquiring new skills and patterns of behaviour. Acquisition and stabilisation of adult personality is important to distinguish and define relationships.
Studies on effect of external conditions and circumstances on adult personality have been studied. However, studies in personality and behavioural patterns among young adult groups, born pre-term are lacking because these groups are recent. The VLBW and very pre-term (VPT) populations are quite overlapping and can be compared only to an extent. Ricards, et al found that VLBW adolescents had lower self-esteem and experienced more social rejection, compared to their normal birthweight (NBW) peers. However, in terms of personality, reduced extraversion and higher neuroticism have been reported. (Allin, 2006)
Pre-term birth is a complex cluster of public health problems with a set of overlapping influencing factors and requires multifaceted solutions. Various causes for pre-term birth such as individual-level behavioural and psychosocial factors, sociodemographic and neighbourhood characteristics, environmental exposure, medical conditions, infertility treatments, and biological factors have been identified. Many of these factors are known to occur simultaneously, particularly in people with a low socioeconomic background or minority status, or people financially weak or members of racial and ethnic minority. Pre-term infants also entail significant emotional and economic costs for families and communities apart from a higher risk of developmental disabilities, health and growth problems. Pre-term birth can also have implications for public-sector services such as health insurance, educational and other social support systems. About 26.2 billion dollars has been reported as the annual societal economic burden associated with pre-term birth in the United States in 2005.
Among the world population, such births have been observed the most in non-Hispanic African Americans and the lowest rate of premature births have been observed in Asians or Pacific Islanders. The rate of pre-term-births in African American women was 17.8%, 11.5% for white women and 10.5% for Asian and Pacific Islander women during 2003. The most prominent increases in pre-term birth rate from 2001 to 2003 were observed for white non-Hispanic, American Indian and Hispanic groups.
Currently, methods of diagnosis and treatment of pre-term labour are inadequate and little is known about the prevention of such births. Also, no test or assessment measures for predicting any pre-term birth exists and efforts at prevention have focussed only on the treatment of women with symptoms of pre-term labour such as delaying delivery so that mother and foetus can be transferred to hospital where appropriate care can be taken. Though such methods have reduced pre-term infant mortality, there is a threat of serious health problems later on for the baby. Thus, therapies and interventions to predict and curb per-term births are important. (Behrman and Butler, 2007)
Two factors, that is, maternal stress and maternal urogenital tract infection, are associated with preterm birth. Bacteria and inflammation in the genital tract of women can lead to preterm birth. Bacterial Vaginosis (BV) is the most common genital tract infection in women of reproductive age. The prevalence of BV during pregnancy is approximately 15 percent to 40 percent. This infection is more prevalent in women who are socio-demographically disadvantaged. The infection is present in majority of early preterm births but is not common in later preterm births. However, there are several issues which still need to be answered about the role of infection in preterm birth. (Wadhwa, 2007).
Periodontal disease is also known to cause preterm deliveries among rural women who abstain from tobacco, alcohol, and drugs. Further, studies based on acquiring this knowledge can educate mothers that even if they feel they are perfectly healthy and free from smoking, alcohol consumption, and drug use, they are not guaranteed to deliver a healthy infant born at term.
Periodontal disease is associated with a chronic Gram-negative infection of the periodontal tissues which results in long-term local elevation of pro-inflammatory prostaglandins and cytokines and an increase in the systemic levels of some of these inflammatory mediators.
Therefore, periodontal disease has the potential to influence preterm birth through a study conducted in Matale, Sri Lanka. 227 subjects were studied, resulting in a cohort of 66 subjects with the exposure and 161 without the exposure. In this study, the authors observed a higher proportion of preterm low birth weight among subjects with higher pocket depths, plaque, and bleeding scores (the exposed group). This can be linked to a series of animal and clinical studies by Offenbacher and co-investigators that indicate an association between periodontal infection and adverse pregnancy outcome. (Rajapakse, Nagarathne, Chandrasekra and Dasanayake.2007)
Studies have shown a higher risk of delivering low-birthweight babies by teenaged mothers and older mothers than mothers aged 20 to 34 years. Interestingly, birth of low birthweight babies has increased among Black mothers, irrespective of their age. This has been associated with "weathering" - a premature decline in health among individuals exposed to harsh living conditions.
Besides maternal age, paternal age has also been found to influence birthweight. A study in Denmark found a positive association between paternal age and pre-term birth. Teenaged fathers were 20% less likely and fathers older than 34 years were 90% more likely than fathers aged 20 to 34 years to have low birthweight babies. It should be noted that these results were obtained after controlling the child's gender, mother's race or ethnicity, birthplace, marital status and health insurance type.
While the associations were significant when maternal age was also controlled, racial or ethnic differences in associations between paternal age and low birthweight were not found. These results suggest that more attention is required to understand the paternal influences on birth outcomes and the interactive effects of urban environments and individual risk factors on health.
The sample under represented parents aged younger than 18 years. Sample sizes prohibited the testing for interaction effects between more advanced age and racial or ethnic categories. Health insurance status is an unsatisfactory substitute for socioeconomic status. The absence of measures of parents' increasing exposure to harsh living conditions prohibited from directly testing the paternal weathering hypothesis. (Reichmann and Teitler, 2006)
Studies on infants born pre-term have also shown that these infants are at a higher risk of developing Attention Deficit Hyperactivity Disorder (ADHD). However, pre-term subjects do not seem to be prone to any major psychiatric disorder, except schizophrenia. Prevalence of low self-esteem and certain drawbacks in personality traits, example neuroticism, in these subjects have also been observed. These traits suggest that pre-term born infants may be at a risk of psychopathology in adulthood. A study conducted by Lindstrom et al, showed that subjects under almost all categories of pre-term births, ranging from very pre-term birth (gestational weeks 24-32) to the early term group (gestational weeks 37-38), were hospitalised for psychiatric disorders in adolescence or young adulthood. Therefore, the results indicate an increase in hospitalisation for psychiatric disorder with an increase in pre-term births. It was observed that most subjects belonged to the moderately pre-term group, a group in need of more attention in research and secondary prevention. However, it remains inconclusive whether pre-term subjects are prone to alcohol consumption or substance abuse. Some findings have suggested a higher likelihood of addictive disorders in pre-term subjects compared to term subjects. (Lindstrom, Lindblad and Hjern.2009)
The cluster of problems in premature children during childhood continues into adolescence as well. These psychosocial and educational vulnerabilities can interfere with their transition into adulthood. In today's high-technology and fast-paced society, pre-terms have to struggle in areas of employment and adapt to their respective workplace demands. Premature subjects experience difficulties in meeting challenges of competition and in gaining social and economic independence. However, no gender differences were found as gender differences improve with age. (Grunau, Whitfield and Fay.2004)
Common prevailing problems among premature subjects, such as higher degrees of inattention, hyperactivity and learning difficulties can affect their temperament and personality. Young adults with VLBW display few negative emotions and are more dutiful, cautious and behaviourally inhibited compared to term-born peers. The above differences between pre-term subjects and term born subjects considerably affect the quality of life in pre-terms.
Various factors define the activities of adulthood. These include leaving the parental home, beginning sexual activity and starting a family. However, in adults born pre-term with VLBW, these important changes of adult life lack attention and have not been therefore documented. Moreover, the scarce data available on these issues among pre-term subjects remains inconclusive. Major differences exist among researchers on this topic. Hack et al. observed that 20-year old women born pre-term with VLBW were less likely to have experienced sexual relationships or given birth than their normal counterparts. Conversely, in a study by Saigal, no difference was observed between extremely low birthweight (ELBW) adults from 22 to 25 years of age and control subjects with respect to sexual relationships and having given birth. However, a high number of VLBW men were noted to reside in their parental homes. Cooke et al observed that most 19 to 22 year old VLBW survivors live with their parents but do not differ in terms of sexual activity. Based on the results of these studies, Kajantie undertook a research to find out whether VLBW subjects really differ from their term-born peers with respect to matters of transition to adulthood, such as leaving the parental home, getting married and starting a family.
At the end of the research, Kajantie et al in their study confirmed that being pre-term really meant a decline in, or affected the quality of life that adults usually enjoy. Their findings suggest that healthy young adults who were born pre-term were slower to leave the parental home, start cohabiting and engage in sexual activity. They also had a smaller number of sex partners. It was also observed that these findings were not affected by other factors such as socioeconomic status, family structure, or school achievement, although shorter height was a possible reason for prevention on sexual activity in VLBW men. Though these findings do not file any disadvantages or benefits, they might impact the way VLBW subjects acquire their place as adults in society. Recent articles suggest that cerebral palsy, deafness, epilepsy and visual impairments make the lives of pre-term subjects further difficult. (Kajantie, 2008)
Affect of socio-emotional and personality processes on adults born pre-term has been neglected in the past. Recent studies suggest a probable risk of emotional and psychiatric problems in adults born pre-term.
Hack (2007) found lower scores among premature subjects for criteria such as risk taking and antisocial behaviour. Allin et al observed a risk of developing mental health problems in very pre-term adults. Schmidt compared the pre-term subjects with term-born on the basis of multiple components of personality that define personality structure. The objective of the study was based on the fact that these components indicate risk of emotional problems. The study extended the work from previous studies by focussing on a regional group of ELBW survivors that may constitute a more vulnerable sample than other samples examined in earlier studies. They also studied the overall personality in this group by focussing on its various components such as temperament, motivation, cognitive and affective component, and socialization. Such an examination of personality enabled a clearer and deeper view of the individual differences in personality type and their affect on the chances of developing psychiatric problems.
Schmidt et al. found that birthweight had an impact on personality. Lower birthweight was associated with higher shyness, behavioural inhibition, loneliness and lie scores (a measure of social desirability) and lower psychoticism scores (a predisposition towards antisocial behaviour). Young adults born ELBW without major impairments were found to be are more cautious, shy, and risk-aversive and less extraverted than their normal birthweight counterparts. These findings suggest that preterms are at an increased risk for developing psychiatric and emotional problems. However, affects of interaction between group and gender on personality were not observed as the ELBW group constitutes a more vulnerable and extreme sample than other groups. Moreover, the risk level because of birthweight alone may be a strong factor for the development of a particular personality style dominating any likely influences because of gender.
It is noteworthy to quote the conclusion from this study by Schmidt et al to understand the goals achieved in the study and the probable direction of future research with respect to ELBW subjects.
"Development is a dynamic process in which fluctuations in initial conditions might be capable of altering the long-term trajectories of psychobiological systems, placing some adults born at ELBW at risk for psychiatric problems". Therefore, there is a need to consider multiple components of personality and how early stress can affect the course of socioemotional and personality processes. Future research should examine the possible differences between ELBW and NBW groups on more objectives supposedly derived behavioural (e.g. measures of direct behavioural observation in stressful situations) and psychophysiological (e.g. measures of electrocortical and cardiovascular responses in resting and stressful situations) measures that are known to guide underlying personality and socioemotional processes in addition to the subjective self-report measures used. (Schmidt, Miskovic, Boyle and Saigal.2006)
It is important for children to develop better reading skills as it holds great value in society and helps to score in education. A study conducted by Monset indicated improvement of language skills among premature children with age. This finding was supported by Ment. These studies indicate a potential for positive long-term change in language skills in VLBW children. These results are in accordance with research indicating that language is less compromised than non-verbal cognition and also with research reporting a high risk of learning disabilities in maths compared with reading. Therefore, it can be concluded based on these studies that some potential for positive long-term change in language skills exists in VLBW children, even though most studies in VLBW children indicate that deficits in cognitive development remain or even worsen up to adolescence.
Most studies have given contrary remarks to Ment's and Monset's findings and reported deficits in reading skills in premature subjects compared with term-born subjects. These researchers tested word decoding, word recognition and reading comprehension in all ages. (Klein, 1989; Marlow, 1991). Another researcher examined changes in reading skills over time and found only some improvement in reading between ages 8 and 10.
However, whether problems in reading skills in 9-year olds that remain unchanged, improve at 15 years of age was proposed to be found. It was found that VLBW children improve their reading comprehension and word recognition skills between 9 and 15 years of age more than NBW children. Therefore, positive outcomes with regard to reading skills can be observed in preterms over time. (Samuelsson, Finnstrm, Flodmark, Gddlin, Leijon, and Wadsby.2006)
According to Aggermaes, quality of life is the fulfilment of basic needs such as biological needs, good relationships, need for meaningful occupations and diverse and exciting experiences. In comparison to other studies, it was revealed that pre-term subjects had positive self-perceived notions about themselves contrary to other's perceptions of prematurity. VLBW subjects reported normal health and functioning but less resilience in matters of physical activity and family involvement.
Giser and Morse recognised three elements i.e. 1. Quality of life is subjective and based on the individual's perception, 2. Quality of life has various dimensions, 3. Quality of life can include objective information i.e. the individual's ability and the individual's subjective appraisal of their quality of life. The effects of pre-term birth on health-related quality of life seem to diminish over time. However, parents of pre-term subjects report dissatisfaction over their offspring on various issues while the subjects themselves do not.
Comparing QoL across age groups was confused by changes in neonatal interventions over time, which influenced outcomes in different cohorts. By only including studies that used a QoL measure, a large body of preterm text that dealt with QoL-related concepts was excluded. (Zwicker and Harris, 2006)
There is growing evidence that brain malformations are linked to pre-term birth. However, it has been difficult to prove this finding as brain defects can be hidden within the cranium and cannot be detected without autopsy. 9.3% of the babies were born without defects, whereas 21.5% of them were with defects. In the autopsy cases with brain defects, the rate of pre-term birth was even greater at 33.1%, showing the strongest association between the two. (Brown et al, 2009)
Low birthweight in infants born at term is associated with metabolic challenges that can lead to obesity, type 2 diabetes and cardiovascular disease later in life. Similar metabolic challenges have been confirmed in premature infants with VLBW. In a comparative study from Finland, young adults born at an average gestational age of 29 weeks and weighing less than 1500 grams had poor insulin resistance, higher serum concentrations of glucose, two hours after a glucose load, and higher blood pressure than similar young adults, born at term. These differences were significant, potentially important clinically, and not explained by differences in body-mass index or body composition.
These data clearly suggest that children born pre-term face various physiological, psychological, developmental, emotional and personal challenges. Research suggests that these challenges persist in their transition to adolescence and even adulthood. This possibly indicates that children born pre-term have higher levels of stress. However, research with respect to stress levels, particularly in young adults is scarce.
This study aims to establish a potential link between stress levels and subjects born pre-term. This study hypothesises higher levels of stress in young adults born pre-term compared with young adults born at term based on a stress questionnaire.
A sample of 60 young adults between the ages of 20 to 25 was taken-30 young adults born pre-term and 30 young adults born at term were selected.
The researcher used a standardised questionnaire, SPSSI (Singh Personal Stress Source Inventory, English version), designed to measure the degree or magnitude of personal stress in persons between the ages of 20-25.It was taken from the National Psychological Corporation (NPC).The questionnaire consists of 35 questions, each giving three choices, namely 'seldom', 'sometimes' and 'frequently', from which the subject has to choose one.
Research DesignIndependent variables-
- young adults born at term.
- young adults born pre-term.
In order to obtain the data required the investigator approached the University of ICFAI.
Data was also obtained from the final year students of St. Francis College for Women. The researcher then approached a few classrooms and established a good rapport with the subjects and asked them to carefully read the instructions given on the first page of the questionnaire which are as follows:-"Following are some of such source events of personal life which often occur. Read these source events very carefully one by one and out of three given response options of each event, namely, 'seldom', 'sometimes' and 'frequently', put a tick mark on the cell below that option which is most suited in your case. The event of the item which does not apply in your case should be left unanswered." The subjects were asked to respond freely and told that their answers will be kept strictly confidential and that there are no right and wrong answers.
The table shows the results of subjects who were born pre-term and subjects born at term in the age group of 20-25 on the SPSSI. The table gives the total of the raw scores of young adults between ages 20-25 born pre-term as 1732 and young adults born at term as 1700.The mean of group-1 is 57.7 and the mean of group-2 is 56.67.The mean difference shows that stress among young adults born pre-term is higher than those born at term. The t-ratio is 0.26. The Standard Deviation (S.D) for group-1 is 15.59 and for group-2 it is 14.51. Through the Mann-Whitney U test, z-score was calculated as 6.65 and its P value is 0.99 which is less than 0.0001, which can be interpreted as extremely statistically significant. Hence, birth factor contributes to stress in young adults born pre-term as proved by the study.
Stress is largely caused when an individual is unable to deal with his or her environment in appropriate ways. Past researches showed that persons born preterm have poor personality styles and mental ability to deal effectively with life demands, which in turn leads to mental or psychological stress. Previous studies have shown a major difference between children and adults born preterm and at-term. However, the present study showed a very little difference of -1.1 between those born preterm and those born at-term which can be said to be inconsistent when compared to past researches.
The present study deals with the magnitude of stress in term born young adults and young adults born preterm. It seeks to find if there exist high levels of stress among young adults born preterm when compared to young adults born at term given that people born preterm go through a difficult life as suggested by earlier studies conducted on preterm children and adults. The major limitation of this study was that a wider age group, such as 15-35, could have yielded better and more clear-cut results. Moreover, we cannot say that subjects who have participated in the study have given absolutely truthful responses, that is, the study was interviewee dependent. However, the major finding of this study suggests that there is hardly any difference between those born preterm and at term. This further suggests that more number of in-depth studies on those born preterm are required so that important facts can be confirmed and preventive measures can be taken in the future. In India, not much research has been done on those who were born preterm and this study can contribute to some extent.
Results from various studies suggest that preventive developmental interventions for LBW, premature infants have verified only modest success. Future research endeavours should investigate the type, duration, critical age onset, and intensity of the intervention as well as which subgroups of LBW infants most benefit from such programs. All chances of preterm or unhealthy deliveries and births in women must be thoroughly investigated and proper care must be taken of pregnant women in terms of mental and physical health, thereby reducing chances of preterm delivery if any. Further research is needed to investigate the actual causes that lead to preterm delivery and the methods to curb preterm birth in children. Proper nutrition especially designed for the benefit of those born preterm can be developed. Future research about anxiety and preterm birth should use valid and reliable measures of anxiety disorders and should focus specifically on preterm birth or spontaneous preterm birth outcomes. Future research could also seek to identify biological pathways, such as blood pressure, mother's age and so on, which are associated with preterm birth outcomes. Such research may help to identify new causes leading to preterm birth.
Thus, through the present research, we may conclude that young adults born preterm are at a somewhat higher risk of showing stress or rather, are stressed, than young adults who were born full-term. The purpose of the research was to find whether young adults born preterm are more stressed than adults born full-term. This research, as expected, gave results which were in accordance with most other researches which concluded that children and adults born low birth weight showed signs of internalised behaviour such as anxiety, depression and so on. However, the degree of stress did not vary much between the two groups.
- Allin M, Rooney M, Cuddy M, Wyatt J, Walsh M, Rifkin L, and Murray R. Personality in young adults who are born preterm. Pediatrics. 2006; 117; 309-316.
- Behrman RE, Butler AS. Committee on Understanding Premature Birth and Assuring Healthy Outcomes. (2007). Preterm birth: causes, consequences, and prevention. National Academy of Sciences.
- Caine, J. (1992). The effects of music on the selected stress behaviours, weight, caloric andformula intake, and length of hospital stay of premature and low birth weight neonates ina newborn intensive care unit. Journal of Music Therapy, 28(4), 180-192.
- Fliege H, Rose M, Arck P, Walter OB, Kocalevent RA, Weber C, and Klapp BF, The Perceived Stress Questionnaire (PSQ) reconsidered: validation and reference values from different clinical and healthy adult samples. Psychosomatic Medicine. 2005; 67:78-88.
- Grunau RE, Whitfield MF, Fay TB. Psychosocial and Academic Characteristics of Extremely Low Birth Weight (800 g) Adolescents Who Are Free of Major Impairment Compared With Term-Born Control Subjects. Pediatrics. 2004; 114:e725-e732.
- Kajantie E, Hovi P, Rikknen K, Pesonen A K, Heinonen K, Jrvenp A L, Eriksson J G, Karlsson S.S and Andersson S.Young Adults with Very Low Birth Weight: Leaving the Parental Home and Sexual Relationships Helsinki Study of Very Low Birth Weight Adults. Pediatrics. 2008; 122; e62-e72.
- Lindstrm K, Lindblad F, Hjern A. Psychiatric Morbidity in Adolescents and Young Adults Born Preterm: A Swedish National Cohort Study. Pediatrics. 2009; 123; e47-e53.
- Rajapakse PS, Nagarathne M, Chandrasekra KB, Dasanayake AP. Periodontal Disease and Low Birth Weight, 2007
- Raikkonen K, Pesonen A, Heinonen K, Kajantie E, Hovi P, Jarvenpaa A L;. Eriksson J G, Andersson S, Depression in young adults with very low birth weight. Arch Gen Psychiatry. 2008; 65(3):290-296.
- Reichmann NE, Teitler JO. Paternal age as a risk factor for low birthweight. Am J Public Health. 2006;96:862-866.
- Samuelsson S, Finnstrm O, Flodmark O, Gddlin P O, Leijon I, and Wadsby M. A Longitudinal Study of Reading Skills Among Very-Low-Birthweight Children: Is There a Catch-up? Journal of Pediatric Psychology. 2006. 31(9); 967 -977.
- Schmidt LA, Miskovic V, Boyle MH, Saigal S. Shyness and Timidity in Young Adults Who Were Born at Extremely Low Birth Weight. Pediatrics. 2008; 122; e181-e187.
- Wadhwa PD, Culhane JF, Rauh V, Barve SS, Hogan V, Sandman CA, Hobel CJ, DeMet AC, Schetter CD, Garite TJ and Glynn L.Blackwell Science Ltd.Paediatric and Perinatal Epidemiology 2001,15(suppl.2),17-29
- Zwicker JG, Harris SR. Quality of Life of Formerly Preterm and Very Low Birth Weight Infants from Preschool Age to Adulthood: A Systematic Review. Pediatrics. 2008; 121; e366-e376.