Infant State Organization: A Longitudinal Study

The study highlights the significant prevalence of preterm and small-for-gestational-age (SFD) infants. In New Zealand, 4% of children are born prematurely, and 9.3% are born SFD. Considering the overlap between these categories, 12.1% of infant births fall into these potentially at-risk groups. This high percentage underscores the need for research to identify precise predictors of later developmental difficulties to enable timely assessment and intervention. Currently, identifying infants most at risk is challenging, as the interplay between developing infants and their social and physical environments is not fully understood. While potential deficits can often be ameliorated during the first year of life, further research is needed to determine the optimal methods for doing so. The American Academy of Pediatrics (1964) definition of low birth weight (below 2500 grams) and very low birth weight (below 1500 grams) is referenced. The study also acknowledges the confounding effect of gestational age and birth weight, a point emphasized by Drillien, necessitating a distinction between prematurity and intrauterine growth retardation (IUGR) in research, which is often not adequately addressed.

The study carefully defines key terms. Infants are categorized as preterm (less than 37 weeks' gestation), small for gestational age (SFD) or small for dates (implying intrauterine growth retardation), and full-term appropriate weight. An infant can be preterm and appropriate for gestational age, preterm and SFD, or full-term but SFD. The importance of distinguishing between the effects of prematurity and intrauterine growth retardation (IUGR) is stressed, as they may have different developmental consequences. The lack of consistent definitions across studies hinders direct comparisons. The study notes that many studies define infants of low birth weight as those below 2500 grams, with those below 1500 grams classified as very low birth weight. This inconsistent application of definitions across various studies is identified as a limitation to comparative research and highlights the difficulties in drawing definitive conclusions from disparate datasets based on clinical impressions.

The impact of socioeconomic status (SES) on prematurity and developmental outcomes is examined. Poverty creates additional stresses for low-income mothers, compounding the challenges of caring for a potentially difficult infant. Prematurity is frequently associated with poor maternal health and lack of antenatal care, both more common among low-SES mothers. Consequently, the prevalence of preterm birth is higher in low-income families than middle-income families. The study acknowledges that SES, along with factors like maternal education, influences both mother-infant interaction and the risk of prematurity. Comparisons are made with previous research from Britain, which showed strong SES effects, and Baltimore studies where SES effects were less apparent, potentially due to differing historical and social mobility contexts.

The document reviews several large longitudinal studies examining the long-term effects of prematurity and SFD on intellectual functioning and behavior. These studies consistently highlight socioeconomic status (SES) as a significant factor influencing outcomes. However, the independent effect of prematurity, regardless of SES, is also noted. While many studies report no overall differences in global IQ scores between preterm and full-term groups, deficits often emerge in specific areas such as language development and visual information processing. The contribution of perinatal illness to later developmental functioning remains equivocal. The inconsistency in findings between different studies is noted, particularly regarding the longevity and severity of observed developmental differences. The document refers to studies by Low et al. (1982), Eaves et al. (1970), Vohr and Oh (1983), Drillien (1970), and Commey and Fitzhardinge (1979), highlighting variations in findings regarding the long-term developmental trajectories of SFD infants, both preterm and full-term.

The review summarizes findings on specific deficits observed in SFD infants, both preterm and full-term. These deficits include language delays, behavioral problems related to neurological deficits, hyperactivity, and school failure, often despite normal performance on global cognitive assessments. This highlights a dissociation between overall cognitive ability and functional impairment. Studies cited note poorer Moro reflexes, sustained grasping reflexes, and difficulties in interaction and motor processes in newborn SFD infants. Long-term follow-up studies show that SFD children frequently experience lower intellectual performance, school problems, and the need for special educational services. The study emphasizes that while the underlying biological factors are significant, the observed problems are susceptible to environmental modification. The need for further research investigating the mechanisms underlying these problems and the interaction between specific aspects of the social and physical environment and SFD infants is highlighted.

This section details the methodology for observing and recording infant sleep states. Observations were conducted in the morning after feeding, beginning when the infant entered a sleep state for six consecutive epochs (one minute) and continuing until a complete sleep cycle was observed. A sleep cycle typically consists of a period of quiet sleep followed by a period of active sleep, potentially including REM sleep. The study notes differences between infant and adult sleep patterns, referencing Roffwarg et al. (1966) regarding the shorter duration of the first sleep cycle in neonates compared to subsequent cycles. The researchers were particularly interested in the length of sleep cycles, the duration of quiet sleep periods, and the overall rate of state changes from one sleep state to another. The chosen methodology aimed to capture a comprehensive picture of the infant's sleep patterns, focusing on variables that could shed light on central nervous system (CNS) functioning and its potential implications for overall development.

The study compared sleep patterns of full-term, preterm, and small-for-gestational-age (SFD) infants. Both preterm and SFD infants showed significantly higher rates of state change compared to full-term infants. These at-risk infants exhibited more frequent transitions between sleep states, including shorter bursts of quiet sleep within active sleep periods and vice versa. This frequent shifting was interpreted as an indicator of disorganization in sleep state patterns. The researchers hypothesized that this sleep disorganization could, if mirrored in waking-state behavior, significantly influence parent-child interactions, particularly in the early stages of life. The finding that both at-risk groups demonstrated less stable sleep patterns compared to full-term infants suggested a potential link between sleep disorganization, neurological organization, and subsequent developmental outcomes.

The study mentions the importance of sleep state organization in relation to Sudden Infant Death Syndrome (SIDS). The potential link between sleep and respiratory patterns and the risk of SIDS is highlighted. Research by Harper et al. (1981) showed that siblings of SIDS victims had longer intervals between active sleep epochs and less frequent short waking periods, suggesting a potential failure of arousal mechanisms. Thoman (1975) reported aberrant rates of state change in a full-term infant who died of SIDS. These studies show the correlation between irregular sleep patterns and potential health risks. This potential connection between sleep state organization and SIDS provides a compelling reason to study the subject comprehensively, emphasizing the significance of understanding the relationship between infant sleep patterns and potential neurological dysfunctions.

The study explored the relationship between sleep state consistency in the neonatal period and later development. The findings indicated a relationship between inconsistent state organization and the development of difficulties by 30 months of age. In a sample of apparently normal infants, those with the lowest consistency indices had a higher incidence of developmental delays, SIDS, hyperactivity, and aplastic anemia. This suggests that inconsistent sleep state organization may reflect central nervous system (CNS) dysfunction. While states like crying and quiet alert are directly involved in social interaction, the clarity, frequency of change, and predictability of sleep states significantly affect the infant's caretaking milieu and therefore influence subsequent development. This finding underscored the importance of considering sleep state variables in understanding the complex interplay between infant physiology and social interaction.

Observations of mother-infant interactions were carried out at two and three months of age (corrected for prematurity in the preterm group). The researchers aimed to observe infants' behavior during typical caregiving routines, such as bathing and feeding. Observations took place in the infants' homes whenever possible, with the observer present while the mother engaged in these routines. The mothers were instructed to act as naturally as possible, as if the observer were not present, to avoid influencing their behaviour. The goal was to understand infants' behavior when awake and receiving care from their mothers. This naturalistic observation approach sought to minimize interference, capturing the dyadic interaction in a more ecologically valid context. The data collected aimed to describe the nature and quality of interactions within each dyad and the impact of infant state and caregiver behavior.

At three months of age, preterm mothers interacted less with their infants' looking, vocalizing, and fussing behaviors and signaled alone less often than full-term mothers. Preterm dyads exhibited significantly lower levels of simultaneous interaction behavior (SIB) compared to full-term dyads at both two and three months. However, the significance of this difference at three months might be partially due to the higher number of males in the full-term group, as SIB levels showed sex differences. Similarly, preterm mothers displayed significantly less maternal interactive behavior while their infants were in the Wake/Alert (W/A) state compared to full-term mothers; again, this difference may be partially influenced by sex differences. While only the preterm decrease in responsiveness to the Quiet/Alert (Q/A) state was statistically significant, both preterm and full-term groups showed a trend indicating a decrease in maternal stimulation over time. At three months chronological age, preterm mothers showed more multimodal interactive behavior and signaled alone more frequently than full-term mothers; however, this difference may be impacted by the aforementioned sex-related biases in the sample.

Comparisons between full-term and small-for-gestational-age (SFD) dyads revealed that SFD infants were more passive than full-term infants. They were significantly more quiescent and less likely to initiate interactions. SFD infants also tended to interact less with maternal vocalizations and looking, showing significantly lower levels than preterm infants on these measures. Conversely, SFD mothers interacted with their infants while playing more often than preterm mothers and slightly more than full-term mothers. They were also more discerning in differentiating between Wake/Alert (W/A) and Quiet/Alert (Q/A) states in their infants compared to the other groups. Despite similar levels of simultaneous interaction behavior (SIB) and mutual gaze, SFD dyads showed lower synchrony levels than preterm dyads which primarily reflects lower levels of infant interactive activity. The different interaction patterns observed suggest distinct underlying mechanisms contributing to lower synchrony in preterm and SFD dyads. Tables are referenced to support these findings.

The study examined the consistency of interaction patterns from two to three months and from three to six months. Maternal interactive behavior (MIB) toward infants in the Wake/Alert (W/A) state showed high consistency across these periods, though the correlation did not reach statistical significance in the full-term group. This high consistency is noteworthy considering the lack of consistency in the W/A state itself. The clarity of the W/A state, compared to the potentially ambiguous Quiet/Alert (Q/A) state, may explain this finding. The study suggests a process of over- and under-stimulation between members of the dyad. Initially passive infants discourage maternal engagement, possibly leading to compensatory infant interaction later. The imbalance at each age negatively impacts development in subsequent months. The study found a relationship between simultaneous interaction at six months and developmental quotients (DQs) at ten months. Levels of maternal interaction and signaling at two months were positively related to four-month DQs, indicating the importance of early interaction patterns for later development.

This section discusses the complexities of assessing infant temperament and its relationship to later development. The study notes that the assessment of infant functioning in a potentially stressful situation, such as administering the Bayley Scales, may not align with maternal ratings of temperament. This is because the Bayley Infant Behavior Record (IBR) is based on general impressions rather than a range of specific situations, unlike the Infant Temperament Questionnaire. The inherent difficulty in objectively measuring infant temperament and the potential for observer bias are highlighted. The text questions whether maternal behavior truly differs across varying infant temperaments or if maternal behavior influences the infant's behavior, thus creating a circularity in assessment. Consequently, the study cautiously concludes that while there might be some consistency between maternal reports of infant temperament and maternal behavior, drawing strong causal inferences is difficult.

The relationship between infant temperament and maternal behavior is explored. Gordon's (1983) study, observing structured play between three-and-a-half-year-old children and their mothers, found differences in maternal behaviors based on child temperament. Mothers used more non-power techniques and talked more to children rated as difficult. They displayed more dependent behavior towards easy children compared to difficult children. However, the study acknowledges the potential for these findings to be influenced by the observational setting and the child's developmental stage. Campbell (1979) found that mothers were less responsive to infants rated as difficult at four and eight months, regardless of observed differences in infant behavior at eight months, which raises questions regarding the direct causal relationship between temperament and maternal responsiveness. The study underscores the complex interplay between infant temperament and maternal behavior, acknowledging that the observed correlations do not necessarily demonstrate a direct causal link.

This section examines the long-term developmental outcomes associated with infant temperament. Studies show that temperamental characteristics, particularly intensity, withdrawal, negative mood, and unmalleability in two-year-olds, are related to differences in reactions to the birth of a sibling (Dunn, Kendrick, & MacNamee, 1981). Thomas and Chess (1981) found correlations between difficult temperament at ages three to five and clinical psychiatric disorders in early adulthood, based on a follow-up of the NYLS sample. Graham, Rutter, and George (1973) also noted the link between temperament and other significant outcomes. The document emphasizes that temperament, viewed as an interactive, social-perceptive construct, plays a role in intellectual and behavioral functioning and maternal/interactive behavior. However, the reliability of temperament measurement is discussed, acknowledging the limitations of some existing scales and highlighting the need for reliable and valid assessment tools.

The reliability and stability of temperament measurement are critically examined. Graham et al. reported low test-retest reliability for their scale, highlighting the challenge of consistently measuring temperament. Hubert et al. (1982) reviewed instruments measuring temperament, reporting moderately high test-retest reliabilities for most infant and toddler dimensions. They cite a median dimension correlation of .84 for the ITQ and a total-test correlation of .86 for the RITQ. Field et al. (1978) found stability in 'difficult' temperament ratings from four to eight months. McDevitt and Carey (1981) demonstrated significant stability across temperament dimensions, while Peters-Martin and Wachs (1980) found longitudinal stability only in specific dimensions (activity, rhythmicity, adaptability, and mood) from six to 12 months. The inconsistencies across studies highlight the complexities of measuring and interpreting temperament stability over time, emphasizing that temperament, while potentially influential, requires refined assessment methods for accurate prediction of long-term outcomes.

This section reviews previous research on the relationship between prematurity (based on birth weight) and developmental delay. Early studies, although valuable for their sample sizes, consistently found prematurity as a significant risk factor for developmental delays and increased incidence of significant handicap and subnormality in premature groups. However, these studies didn't always distinguish between prematurity and intrauterine growth retardation (IUGR), a point acknowledged as a limitation. The impact of socioeconomic status (SES) varied across studies, with clear effects noted in British studies but apparently negligible in a Baltimore investigation. This discrepancy is briefly discussed, possibly due to differences in social mobility and attitudes toward child-rearing across the two regions. The studies provide a context for the current investigation, highlighting the existing knowledge gap regarding the precise mechanisms linking prematurity to developmental outcomes.

The section presents a review of longitudinal follow-up studies of preterm and small-for-gestational-age (SFD) infants, emphasizing the inconsistencies in findings regarding developmental outcomes. Some studies found persistent differences between preterm and full-term groups even after controlling for social class variables (Neligan et al.), while others found no significant differences between SFD and appropriate-for-gestational-age (AFD) groups at six years of age (Low et al., 1982). Contradictory results are reported across various studies, with some showing higher scores for SFD preterm infants in their first year, followed by lower scores later (Eaves et al., 1970), while others noted lower scores for SFD preterm infants until three years, with no differences thereafter (Vohr and Oh, 1983). Further discrepancies arise from studies that report higher frequencies of borderline intelligence in preterm SFD infants (Drillien, 1970) versus those showing no significant differences in global IQ but deficits in specific areas like language and visual processing. These discrepancies highlight the need for more rigorous longitudinal studies to clarify the developmental trajectory of these infants.

This part focuses on specific developmental domains and the assessment tools used to evaluate them. Studies using the Bayley Mental Development Index (MDI) at 12 and 24 months found that cognitive development was not predicted by early interactive variables but was influenced by birth status (preterm vs. full-term). Maternal verbal responsiveness, measured by the Home Observation for Measurement of the Environment (HOME) scale, was related to three-year Stanford-Binet scores. The use of various assessment tools is mentioned, including the Bayley Scales, Stanford-Binet Intelligence Scales, Weschler Intelligence Scales, and the Bender Gestalt test. It is noted that the omission of certain subtests (e.g., comprehension and picture arrangement on the Weschler Scales) might have resulted in overlooking subtle visual or language deficits. The section highlights the importance of using comprehensive and sensitive assessment tools to capture the nuances of developmental progress in preterm and SFD infants, particularly in light of the variable findings across previous studies.

The section summarizes findings from longitudinal studies of preterm and SFD infants, concluding that outcomes are frequently less optimal than for appropriately grown infants, regardless of whether they are preterm or full-term. Specific deficits in language, behavior (associated with neurological deficits), hyperactivity, and school performance have been noted despite normal global cognitive assessments. While the underlying biological insults are significant, environmental factors play a crucial modifying role. Studies show that the impact of socioeconomic status (SES) on intellectual functioning and behavior is considerable, although findings regarding the relationship between SES and developmental outcomes are inconsistent. The review emphasizes that while some studies show catch-up in development, there's a persistent risk of specific deficits. The lack of research into the precise interactions of SFD infants and their parents during the first year is highlighted, emphasizing the need for further investigation into the mechanisms that shape these developmental trajectories, particularly given the subtlety and specificity of deficits often observed.