Course:KIN366/ConceptLibrary/Young-for-Date/

Young-for-Date
KIN 366
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Instructor:	Dr. Shannon Bredin
Email:	shannon.bredin@ubc.ca
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Introduction

Preterm infants (also known as young-for-date infants) encompass the population of neonates born before full term. Preterm infants often face greater complications early in life as well as motor, social, and cognitive developmental delays. As such preterm infants are a delicate population of children in need of the most advanced clinical assessments, treatments, and therapies to ensure they are able to catch up to their full-term cohort (US National Library of Medicine, 2011).

Definitions

Young-for-date (also known as a preterm infant): an infant born at expected birth weight for gestational age but before full term (37 weeks of gestation or 3 weeks before due date). (US National Library of Medicine, 2011)

Chronological age: time elapsed after birth and an individual’s age according to standard calendar days. (American Academy of Pediatrics, 2004; Gabbard, 2008)

Biological (developmental) age: determined through measurements such as morphological age, dental age, sexual age, and skeletal age to assess level of maturity. (Gabbard, 2008)

Gestational age: length of time during pregnancy – measured in weeks from the first day of a woman’s last menstrual cycle to the current date. A normal gestational age is 40 weeks. (Kramer et al., 2001)

Conceptional age: length of time from fertilization to birth of the infant. A normal conceptional age is 38 weeks. (American Academy of Pediatrics, 2004).

Low Birth weight: infants born after a regular gestational period of 38-42 weeks but weigh less than 5.5 pounds. (Gabbard, 2008)

Inter-pregnancy interval: the length of time between pregnancies. (Goldenberg et al., 2008)

Miscarriage: the loss of a pregnancy in the first 20 weeks. (Gabbard, 2008)

Stillbirth: loss of a baby after 20 weeks of pregnancy. (Gabbard, 2008)

Fetal & Neonatal Development

Development periods

Prenatal period: period of conception to birth. This period comprises two important stages: 1) Geminal period: from conception to two weeks post-conception. During this period the fertilized egg implants to the uterine wall. 2) Embryonic period: beings when the blastocyst attaches to uterine wall and ends by the eighth week post-conception. This is a critical period of development during which teratogens have the greatest effect on embryonic development. Myogenic movements (muscle movement without neural or external stimulation) may be observed by the end of this period. 3) Fetal period: 8 weeks post-conception to birth. This is a period of rapid growth in size and future cell differentiation.

Neonate period: period from birth to one month. This is an important window for observing initial motor responses. (Gabbard, 2008)

Key landmarks of late fetal growth

It is important to understand key late fetal growth landmarks to comprehend the development processes during pregnancy which may have been missed by an infant born before full-term.

Week (Gestational age/Growth and Development Observed

20: Legs have grown; myelination of spinal cord

24: Respiratory-like movements begin; cerebral cortex layers formed

28: Increasing fat-tissue development; retina layered and light-receptive

32: Weight increasing more than length; taste sense operative

36: Body more rounded; ossification begins in distal femur

40: Skin smooth and pink, moderate head hair; proximal tibia beings ossification; myelination of brain begins

(Larsen, 2001)

Age of viability

Age of viability is the age at which a fetus is able to survive outside the uterus (Moore & Persaud, 1998). The National Institute of Child Health and Human Development (NICHD) found that mean survival rates at 23, 24, 25 weeks gestational age were 30%, 52%, and 76%, respectively (Lemons et al., 1996). Age of viability is important as the fetus may survive outside the womb but will very likely encounter development and organ complications.

Preterm birth

Causes of pre-term birth

There are three main precursors leading to preterm birth (Goldenberg et al., 2008).

Cause/Prevalence:

1. Delivery for fetal or maternal indications (ie. Induced labor or caesarean section) 30-35%

2. Spontaneous preterm labor with intact membranes 40-45%

3. Premature rupture of membranes (PPROM) 25-35%

Spontaneous preterm labor and PPROM are collectively known as a syndrome, which results from multiple causes such as infection or inflammation, vascular disease, and uterine over-distension. Moreover, of these three causes the number of preterm births that have been medically indicated (ie. Caesarean section) since 1989 has increased by 50% (Goldenberg et al., 2008).

Factors that increase the risk of a preterm birth

It is important to note that no single factor has been found to be the cause of preterm birth. However, factors associated with preterm birth have been identified. Drug use, smoking, maternal age (teenagers or older mothers), excessive weight gain, history of miscarriage, adverse social and economic conditions, periodontal disease, stress, prenatal care, previous pre-term birth, African-American (preterm birth rates = 16-18% vs. Caucasian preterm birth rates of 5-9%), low maternal body-mass index have been associated with higher rates of preterm births. In addition, the length of time between pregnancies, known as the inter-pregnancy interval, less than six months doubles the risk of a preterm birth (Goldenberg et al., 2008).

Maternal nutritional status especially low serum iron, folate or zinc have been associated with higher rates of preterm births than those with levels in the normal range (Goldenberg et al., 2008). Moreover, multiple gestations account for 15-20% of all preterm births (Goldenberg et al., 2008). Wen et al. (2004) also found stressful occupation, low maternal pre-pregnancy BMI, poor or excessive weight gain, unmarried or not living with partner, and low education were associated with a heightened risk of preterm birth.

History, Statistics, and Trends of Preterm birth

Preterm births account for 70% neonatal deaths and up to 75% of neonatal morbidity (Wen et al., 2004). Moreover, the rate of infants born preterm has been increasing since the 1980s. Consequently, 5-11% of infants were born preterm in industrialized countries in 2004 (Wen et al., 2004). To further illustrate, in 2001 preterm delivery rate was reported as 11% in the USA, 5-7% in Europe, and 6.5% in Canada (Joseph et al., 2001).

Researchers have suggested that this increase in preterm births is perhaps due to the focus of clinicians and researchers on treatments for preterm infants rather than prevention of preterm births (Wen et al., 2004). Consequently, changes in neonatal care during the last 20 years have increased the chances of survival at week 23 from 0% to 65% in some health care centers (Ward & Beachy, 2003).

With these statistics in mind, there is a comprehensive need for further research in prevention, diagnosis, assessment, and treatment for infants born preterm. Moreover, studies investigating the long-term effects of preterm birth on motor, social, and cognitive development are critical to improving infant outcomes.

Concerns with pre-term birth

General concerns for preterm infants

Early challenges premature infants may experience are problems with: breathing regularly on their own; due to their underdeveloped lungs, body temperature regulation, feeding and growth problems due to an immature digestive system, jaundice, and anemia (Torpy, 2005).

There is an increased risk for the development of neurological impairments, respiratory, and gastrointestinal complications with preterm infants. As such, respiratory distress syndrome and brain injury during prenatal period are the major causes of morbidity and mortality in preterm infants (Fraser et al., 2004). Despite new advances in treatment such as prenatal corticosteroids and postnatal surfactant administration, many preterm newborns continue to develop bronchopulmonary dysplasia (Ward & Beachy, 2003). In addition, there is a high risk of severe intraventricular hemorrhage or neurological impairment leading to illnesses such as cerebral palsy (Ward & Beachy, 2003).

Neuroplasticity

Pitcher et al. (2011), state that neuroplasticity is the brains lifelong ability to make short-term or long-term modifications to the strength and number of its synaptic connections in response to incoming stimuli associated with activity and experience. Neuroplasticity is most prominent during the early stages in life due to rapid brain growth and brain complexity, which includes creating synaptic connections and experience-dependent pruning of these synapses (Pitcher et al., 2011). Neuroplasticity can either exacerbate or enhance postnatal outcomes.

Enriched Environments

Environments that promote enrichment seem to have positive effects on outcomes at all ages, although animal studies suggest that exposure to these environments before adulthood may have additional positive effects on the developing brain (Pitcher et al., 2011). Some characteristics of enriched environments include a stable family support system, financial stability, as well as physical activity being a key component for having positive neurological outcomes.

Adverse Outcomes

Premature infants experience a lot of stress in early life. They have an excess of glucocorticoids, which is common in premature infants, as well as they are often given exogenous steroids prenatally to mature the respiratory system (Pitcher et al., 2011). Although this exposure is beneficial for short-term survival, excess glucocorticoids in early life can lead to alterations in programming of developmental changes and could lead to behavioural and functional consequences (Pitcher et al., 2011). This increase in cortisol increases the stress response for preterm infants, who are already stressed because of their immature organ systems, and it also reduces the ability for neuroplastic reorganization, and therefore affects learning and memory functions (Pitcher et. Al., 2011).

Movement Experiences

Important Factors Influencing Motor Development

• Insufficient postnatal growth (weight, height, head circumference)

• Brain maturation proceeds in a different way than full term infants

• Small muscle size

• Lower proportion of fast-twitch muscle fibers

• Reduced intramuscular high-energy phosphate

• Physical hypoactivity may cause the anaerobic performance to be lower

• Inferior muscular coordination

• Poor muscle strength

• Poor muscle power regulation, resulting in inadequate postural control, can affect the quality of movement and result in a delayed onset of antigravity activities

(Van Haastert et al., 2006)

Motor development specific concerns for preterm infants

Preterm survivors are at a higher risk for a complex and inter-related range of motor, cognitive, sensory, behavioural, and health problems compared with infants born at term (Spittle et al., 2009). For example, Retinopathy of Prematurity (ROP) is an abnormal blood vessel development in the retina of the eye. ROP is a frequent cause of neurosensory impairments in extremely preterm infants. Moreover, ROP results in severe vision loss which hinders both sensory and motor development (Ward & Beachy, 2003). Other visual impairments include strabismus, refractive error, poor contrast sensitivity and poor stereovision (Fawke, 2007). Another neurosensory impairment preterm infants encounter is deafness and auditory discrimination problems. Those who are at highest risk are smaller babies who have had septicaemia, have high serum bilirubin levels or have received sufficient doses of ototoxic drugs (Fawke, 2007).

Neurological Outcomes

Preterm infants are born during a period of rapid brain growth and maturation, making their brain highly susceptible to brain injury (Lenke, 2003). It is found that impaired motor and cognitive development remain to be the two major adverse outcomes of being born prematurely (Pitcher et al., 2011). The brain is prone to injury due to the difficulty with blood flow regulation and the disruption of blood flow, and therefore oxygen to the brain, although it is not uncommon for young for date infants to develop motor impairments without an apparent brain injury (Lenke, 2003). The more premature the birth is the greater the adverse effects are to normal growth trajectories, meaning that the pattern is brain injury is highly dependent on gestational age (Pitcher et al., 2011).

Cognitive Outcomes

There is new evidence that the motor areas of the brain also contribute to cognitive processes that include speech perception and learning, which explains why motor and cognitive dysfunction often co-occur (Pitcher et al., 2011). According to Pitcher et al., (2011), up to 50% of children born before 33 weeks gestational age have cognitive difficulties that are associated with motor dysfunction. These include an increased risk of learning difficulties, especially in reading and language. These findings support the motor areas of the brain also contributing to higher cognitive processing which include speech and language processing as well as their primary function in movement control (Pitcher et al., 2011). Due to this connection between cognitive and motor areas, there is available evidence that suggests by improving a preterm child’s motor development may have subtle but significant effects on their cognitive outcomes (Pitcher et al., 2011).

Motor Outcomes

The area of the brain that is most prone to injury is the periventricular area which has an impact on motor function (Lenke, 2003). Periventricular leukomalacia is a condition that describes the cell death of the white matter surrounding the lateral capsules, which is strongly correlated with motor impairments, especially ones that impact the lower extremities (Fawke, 2007). A common motor disability that is prevalent in premature infants is cerebral palsy, which is a disorder of movement and posture that is acquired early in life due to brain abnormalities (Pakula et al., 2009).

In the first few months of life preterm infants exhibit more extension and difficulty with movements against gravity. This relative dominance of extensor tone is demonstrated by a prevalence of neck hypertension, decreased anti-gravity movements, and decreased midline movements. Moreover, infants born even a few weeks before their full term counterparts exhibit much lower muscle tone both actively and passively. This may be a consequence of long hospitalization periods due to respiratory or cardiac complications where preterm infants are immobilized for long periods of time resulting in gross motor delays in head and trunk control (Spittle et al., 2009).

Preterm infants often demonstrate an uneven progression of motor development compared to their full-term counterparts. Researchers postulated that this may be due to an imbalance between active flexor and extensor strength which may lead to inadequate postural control. (Pin et al., 2009).

Premature infants may also have difficulty transitioning between postures due to hypertonia or hypotonia that persists in extremely premature cases (Lenke, 2003). This can also lead to a delay in the development of trunk rotation and strength, and reciprocal crawling may be delayed (Lenke, 2003).

Working with preterm infants

Corrected age

Corrected age is most appropriately used to describe children up to 3 years of age born preterm. This term represents the age of the child from the expected delivery date. This number is calculated by subtracting the number of weeks born before 40 weeks of gestation from chronological age (American Academy of Pediatrics, 2004). For example, if a child was born at 32 weeks when he/she reaches 6 months chronological age their corrected age would be approximately 4 months. The use of corrected age is critical when assessing motor behaviour as chronological age has been identified as an invalid and inaccurate mean to determine motor delay in preterm infants (Allen & Alexander, 1990).

Early childhood educators, pediatricians, physical therapists, and parents are recommended to use corrected age when working with preterm infants. Corrected age is particularly useful for comparing preterm motor development to full-term counterparts (Allen & Alexander, 1990).

Reflexes

Preterm primitive reflexes including the moro and the palmar grasp, may be absent or persist longer than expected for a full-term infant (Lenke, 2003). This absence or long-term appearance may be due to neurological or muscular abnormalities resulting from preterm birth. Scholarly and clinical work emphasizes the importance of using an infant’s corrected age (not chronological age) for clinical reflex assessment (American Academy of Pediatrics, 2004).

NICU

A Neonatal Intensive Care Unit (NICU) is a care unit specialized in caring for sick or premature newborn infants. Although their priority is to care for the infants, adverse side effects can occur, which can affect their short-term or long-term neurodevelopment. These can include invasive painful procedures, increased light and noise, maternal and paternal separation, effects of acute or chronic illness, and too little or too much tactile stimulation (Pitcher et al., 2011). This has led to care strategies including the Newborn Individualized Developmental Care and Assessment Program, and Kangaroo Mother Care (Pitcher et al., 2011). Early NICU experiences may also influence motor development. The positioning of preterm infants has a significant impact on the progression of abnormal motor signs (Fawkes, 2007). For example, placing an infant in constant prone positions can result in shoulder retraction, external hip rotation, chest flattening, and plagiocephaly; which results in excess extensor hypertonicity in the trunk and legs as well as hypertonic hip adductors and delayed supporting responses (Fawkes, 2007). Motor development may also be impaired by chronic lung disease. This is due to additional accessory muscle use and chronic fixation of the rib cage to optimize the work of breathing, but is also due to placing the infant in a prone position more regularly which reduces the work of breathing (Fawkes, 2007). Bringing awareness to these issues has seen a decline in their occurrences. The length of time in the NICU can also lead to secondary complications such as a decreased opportunity to engage in movement, which may interfere with the acquisition of early motor skills (Lenke, 2003).

Assessment methods:

When assessing movements, it is important to consider why the movement pattern may be abnormal. It could be related to prematurity or it could be that the infant had little opportunity to engage in an activity and therefore development does not occur typically due to lack of experience (Lenke, 2003). For example, infants who do not engage in prone play, may crawl later due to lack of experience in pushing themselves up from their stomachs and therefore not developing sufficient chest and arm strength.

When working with preterm infants it is important to understand that development trajectories may be different than a full-term infant. As such it is critical to use adjusted norms for proper evaluation and clinical decision-making when working with preterm infants. Pediatricians and physical therapists typically use the assessment methods listed below.

White Matter Abnormality (WMA)

WMA is assessed by MRI and was found to be 100% accurate in predicting cerebral palsy in preterm infants. In addition, this measurement technique has also been found to be predictive of later neurodevelopmental impairments in very preterm infants. (Spittle et al., 2009)

General Movements

This method also known as Prechtl’s method of assessing spontaneous movements and proven to be more valid than neurologic examination in predicting long-term outcome of preterm infants. In a study by Spittle et al. (2009), researchers found that general movements assessed at 1 and 3 months’ corrected age significantly correlated with Alberta Infant Motor Scale (AIMS) and Neuro-Sensory Motor Development Assessment (NSMDA) scores at one year of age.

Alberta Infant Motor Scale (AIMS)

AIMS is the most common motor development assessment tool cited in the literature. This assessment tool is intended to measure gross motor maturation and identify motor delays from birth to independent walking (18 months). Four key positions are evaluated: prone, supine, sitting, and standing. Infants are then assessed based on their weight bearing, posture, and antigravity movements (Piper et al., 1992).

AIMS accounts for differences and delays in preterm infants as motor development trajectories for both full-term and preterm infants are plotted against population data. In addition, AIMS can also be used to assess infants at risk of developmental delay and infants diagnosed with disorders or conditions causing delayed motor development such as Fetal Alcohol Syndrome, Down syndrome, seizure disorders, and bronchopulmonary dysplasia.

AIMS is a unique motor assessment method as it can be used to evaluate and track motor development over time. However, it is important to note that AIMS was not intended to evaluate older children with motor abilities still at an infant level.

Procedure: AIMS uses an easy rating system divided into four positions with pictures to demonstrate the capabilities practitioners are looking for. This observation-only assessment takes approximately 20-30 minutes and is best conducted on an examination table for young infants (0-4 months) and a carpeted or mat area for older infants. In addition, a bench or chair will be needed to observe the pull to stand, standing, and cruising items in the standing subscale. The ideal setting for AIMS is a warm quiet room such as a living room or clinic. Parents and/or caregivers are encouraged to be involved in the assessment and toys should be used to engage the infant. The infant should be naked, whenever possible, and should be awake, active, and content during the assessment (Piper & Darrah, 1994).

The AIMS form is simple to use and contains guidelines to assist the practitioner identify motor behaviours. In each subscale the practitioner identifies the most mature item the infant can sustain and attributes 1 point for this item and all less mature items. The practitioner adds the points in all four sections and plots this number against corrected age to compare the infant’s motor development to population data.

Neuro-Sensory Motor Development Assessment (NSMDA)

NSMDA is used by clinicians to assess motor development of children from 1 month to 6 years of age. This assessment technique identifies areas of concern and of abnormal or dysfunctional components of movement. NSMDA is a “valid, criterion referenced, standardized test” assessing motor development and has been used in Australia and around the world for the past twenty years (NSMDA, 2014). Advantages of this assessment include the use of a criterion-referenced test where the infant’s performance is measured against a set standard on several items rather than compared to the performance of a large peer group (Bruns et al., 1989). The NSMDA assessment can be modified to track preterm infant motor development by allowing clinicians to use corrected age.

Strengths and Limitations of Assessment Methods

NSMDA does not assign an observed/not observed judgment to each movement as is required of the AIMS assessment. With the NSMDA assessment, scorers are required to use a ranking scale and rate the infant based on observation. In addition, NSMDA can be used to track motor development up to six years of age whereas the AIMS assessment can only be used up to two years of age. Moreover, WMA requires the use of a MRI which is expensive and likely not readily available or justified for every preterm infant.

Both NSMDA and AIMS are easy to use scales with clear, standardized outcomes. In addition, both tests have been shown to accurately describe, predict the trajectory, and identify concerns in a preterm’s infant development.

Critique for Assessments

Most follow-up assessments for high risk children is at 2 years of age. However it was argued first by Nelson and Ellenberg in 1982 that this early of an assessment may be inaccurate (Fawke, 2007). They argued that 4 years should be the minimum age in which investigators are allowed to properly differentiate between normal trajectory, slow motor development and abnormal pattern motor development. This was suggested due to the fact that they saw children who were diagnosed with Cerebral Palsy at a young age, grow out of the symptoms (Fawke, 2007). Early assessments provide fast clinical feedback, but it should be understood that this may be unreliable particularly in those that are observed to have less severe disabilities (Fawke, 2007).

Furthermore, Van Haastert et al. (2006) compared mean Alberta Infant Motor Scale (AIMS) scores of preterm infants and full term infants, and concluded that adjusted norms should be used for proper evaluation and clinical decision making in regards to preterm infants. Their study found that preterm infants scored "significantly lower at all age levels, even when corrected for degree of prematurity". Since early motor developmental trajectories of gross motor development are shown to differ between the two groups in the first 18 months of life, standard scales used for full term infants should be adjustable to enable proper evaluation of preterm infants (Van Haastert, 2006).

Practical Applications

When working with preterm infants, studies have shown that these infants can be expected to follow sequential gross motor development at a rate adjusted for their degree of prematurity (Allen & Alexander, 1990). However, it is also important to consider that the rate of development in preterm infants is less predictable because of developmental lags and catch up periods. This is especially important for parents as differences in rates of reaching particular motor milestones may vary and are not necessarily indicative of a medical problem. For example, a delay in trunk and head control in infants may be due to hospitalization, which required long periods of immobilization. In turn, this explains the motor development delay and should serve as an indicator for parents, early educators, and clinicians to strengthen muscles of the head and trunk.

The most practical and applicable methods of motor development assessment include AIMS and NSMDA evaluation methods and are helpful for pediatricians, physical therapists, educators, and parents to track motor development. The most important tool when assessing preterm motor development is to adjust for expected developmental delays by using an infant’s corrected age as opposed to their chronological age.

Tips for practitioners, parents, and educators

Constant assessment and checkups during the first year and beyond are key to early detection and successful motor development. Moreover, multidisciplinary approaches to preterm infant health and development have been very successful. Clear communication between parents, doctors, nurses, physical therapists, and educators is essential to ensure expectations are adjusted and motor, cognitive, and sensory development milestones are met.

Tips for parents

Parents should access resources to better understand the global development of their preterm infant and always ask clinicians when unsure or concerned with their child’s health and/or development. Resources such as the National Perinatal Association’s Multidisciplinary Guidelines for the Care of Late Preterm Infants are excellent resources for parents of preterm infants.

Tips for physical therapists

There has been some controversy in the literature with respect to the effect of early physical therapy interventions and preterm infant outcome. Yigit et al. (2002) reported that there was no difference in the prevalence of cerebral palsy between controls and preterm infants receiving early interventions. Similarly, Cameron et al. (2005) reported that physical therapy intervention does not significantly effect pre-term motor performance. The authors also note that parental compliance and intervention frequency likely influenced these results. As such additional research on physical therapy interventions for preterm infants is needed and will likely promote the advancement of this field.

Conclusion

There are documented negative consequences of preterm birth on social, cognitive, and especially motor development. A clear understanding of the causes and implications of preterm birth as well as the long-term motor challenges encountered during infancy are critical to holistically comprehend preterm motor development. With the prevalence of preterm births increasing, additional clinical research investigating the most comprehensive assessment, prevention, and treatment methods are needed (Wen et al., 2004). Such clinical reports have the potential to improve the lives of preterm infants and provide clinicians, educators, and parents with the tools to assist and facilitate social, cognitive, and motor development.

References

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Pakula, A. T., Van Naarden Braun, K., Yeargin-Allsopp, M. (2009). Cerebral Palsy: Classification and Epidemiology. Physical Medicine and Rehabilitation Clinics of North America, 20(3), 425-452. doi:10.1016/j.pmr.2009.06.001

Pin, T. W., Darrer, T., Eldridge, B., Galea, M. P. (2009). Motor development from 4 to 8 months corrected age in infants born at or less than 29 weeks' gestation. Developmental Medicine & Child Neurology, 51(9), 739-745. doi: 10.1111/j.1469-8749.2009.03265.x.

Piper, M. C. & Darrah, J. (1994). Alberta Infant Motor Scale (AIMS). Retrieved from: http://umanitoba.ca/libraries/units/health/medrehab/measures/albertainfant.html

Piper, M. C., Pinnell, L. E., Darrah, J., Maguire, T., Byrne, P. J. (1992). Construction and validation of the Alberta Infant Motor Scale (AIMS). Canadian Journal of Public Health, 83, 46-50. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/1468050

Pitcher, J. B., Schneider, L. A., Hons, J.L.D., Ridding, M.C., Owens, J.A. (2011). Motor System Development of the Preterm and Low Birth Weight Infant. Clinics in Perinatology, 38(4), 605-625. Retrieved from: https://www-clinicalkey-com.ezproxy.library.ubc.ca/#!/content/playContent/1-s2.0-S0095510811001047

Spittle, A. J., Boyd, R. N., Inder, T. E., Doyle, L. W. (2009). Predicting Motor Development in Very Preterm Infants at 12 Months’ Corrected Age: The Role of Qualitative Magnetic Resonance Imaging and General Movements Assessments. Pediatrics, 123, 512-517. doi: 10.1542/peds.2008-0590

Torpy, J. M. (2005). Premature Infants. The Journal of the American Medical Association, 294 (3). doi:10.1001/jama.294.3.390.

Ward, R. M. and Beachy, J. C. (2003). Neonatal complications following preterm birth. BJOG: An International Journal of Obstetrics & Gynaecology, 110, 8–16. doi: 10.1046/j.1471-0528.2003.00012.x

Wen, S. W., Smith, G., Yang, Q., & Walker, M. (2004). Epidemiology of preterm birth and neonatal outcome. Seminars in Fetal and Neonatal Medicine, 9(6), 429-435. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/15691780

Wood, N. S., Marlow, N., Costeloe, K., Gibson, A. T., Wilkinson, A. R. (2000). Neurologic and developmental disability after extremely preterm birth. New England Journal of Medicine, 343, 378–384. doi: 10.1056/NEJM200008103430601

van Haastert, I. C., de Vries, L. S., Helders, P. J., Jongmans, M. J. (2006). Early gross motor development of preterm infants according to the Alberta Infant Motor Scale. Journal of Pediatrics, 149(5), 617-622. doi: 10.1016/j.jpeds.2006.07.025

Yiğit, S., Kerem, M., Livanelioğlu, A., Oran, O., Erdem, G., Mutlu, A., Turanli, G., Tekinalp, G., Yurdakök, M. (2002). Early physiotherapy intervention in premature infants. Turkish Journal of Pediatrics, 44(3), 224-229. Retrieved from: http://europepmc.org/abstract/MED/12405434