Fetal movement (FM) is an important variable of study as an indicator of prenatal neurological functioning (Prechtl & Einspeler, 1997). Because FM can be easily observed by both the mother and the physician, it is a straightforward marker for impending fetal distress, which, if caught and treated early enough, may be prevented. Although FM is a valuable marker for current fetal functioning, its long-term significance is unknown. FM may also be associated with postnatal functioning; consequently, determining the birth and postnatal correlates of FM is both scientifically and clinically useful.
FM Development in Early Pregnancy
The first spontaneous FM has been found to occur between 7 and 8.5 weeks gestation (De Vries, Visser, & Prechtl, 1982; Van Dongen & Goudie, 1980; Ianniruberto & Tajani, 1981), providing concrete evidence that FM emerges not at quickening, or the time at which the mother first feels FM, but much earlier in gestation. These early movements also show that the behavioral repertoire of the fetus is not solely reflexive in nature because these observed movements (e.g., yawning, stretching, limb movements, etc.) are spontaneous and not elicited. In addition, very early fetal movements are not random, but show systematic organization in that distinct types of movements are regularly observed (DeVries et al., 1982). This organization of behavior implies that these fetal movements are a directly observable manifestation of central nervous system development (Prechtl, 1984).
FM Development in Late Pregnancy
As gestation progresses, a developmental shift in FM occurs at approximately 24 weeks, whereby FM incidences decrease in number and the time between distinct instances of FM increases. Space constraints in the uterus and increasing neurological maturation have been suggested to account for these quantitative changes in movement (DElia, Pighetti, Moccia, & Santangelo, 2001; DiPietro et al., 1996a; ten Hof et al., 1999). Though fetuses may move less after 24 to 28 weeks gestation, their movements increase in vigor (ten Hof et al., 1999; DElia et al., 2001). Despite large variability among fetuses, they typically move once per minute and are active 20 to 30 per cent of the time (DiPietro et al., 1996a). A slight discontinuity in FM has also been observed at 28 to 32 weeks gestation, where the rate of FM slows. This decreased rate of FM may be a consequence of changes in neurological organization that may enable the fetus to live outside the uterus after 32 weeks gestation (DiPietro et al., 1996a).
The developmental function (DF), or the plot of FM measured repeatedly over time, has also been studied, providing a qualitative description of FM in the last trimester (see Richards, Newbery, & Fallgatter, 1938; Edwards & Edwards, 1970; Eaton & Saudino, 1992). The overall pattern is an inverted-U shape, with FM increasing through the eighth month and then decreasing in the ninth month. Two possible explanations of the shape of the DF have been offered: increased pressure on the fetuss head and increased fetal size leading to space constraints may inhibit FM (Richards et al., 1938).
Deviations from the average inverted-U-shaped function have been noticed (Richards et al., 1938; Eaton & Saudino, 1992), indicating that there are substantial individual differences in DF. For example, Eaton and Saudino (1992) plotted individual FM counts (determining DF for each individual), and approximately half of the fetuses studied did not conform to the mean DF. In fact, some fetuses show the entirely opposite pattern (i.e., increases in activity as the third trimester progresses). Though the subject-by-subject plots are purely descriptive, they do provide strong evidence of between-fetus variability in the DF of FM, highlighting its possible utility as an individual differences variable that may provide more information on fetal neurobehavioral development.
Fetal Behavior and Infant Development
FM and Infant Activity
The importance of determining whether FM and infant AL are each manifestations of the same underlying trait, and therefore continuous, or two discrete behaviors is two-fold. First, both FM and infant AL have been shown to be indicators of neurological health and functioning (Prechtl, 1984). If FM and infant AL are, in fact, the same underlying trait, then infant neurological health can be determined well before birth by assessing FM. Second, determining whether or not FM and postnatal AL are continuous would help to elucidate the underpinnings of motor activity, a core dimension in nearly every theory of temperament, by allowing AL to be studied at its beginnings and earliest points in development (DiPietro et al., 2002).
Continuity between prenatal and postnatal activity has been observed (Ishikawa & Minamide, 1984; DiPietro, Hodgson, Costigan, & Johnson, 1996b; Almli, Ball, & Wheeler, 2001; Groome, Sweiber, Holland, Bentz, Atterbury, & Trimm, 1999). FM, in general, is significantly associated with infant AL immediately after birth (Almli et al., 2001) through 2 years of age (DiPietro et al., 2002). Specific movements (i.e., jaw movements, stretching, isolated leg movements, etc.) are continuous across birth. For example, qualitatively similar stepping movements have been observed in the same individual both immediately before and after birth (Prechtl, 1987; Almli et al., 2001). Sex differences in the relation between FM and AL at 1 and 2 years have also been observed (DiPietro et al., 2002)
FM and Other Dimensions of Infant Temperament
FM predicts infant temperament at 3 and 6 months as measured by parent report (DiPietro et al., 1996b). Specifically, the more active fetuses were more difficult, less predictable and less adaptable infants, suggesting that FM is related to behavioral regulation in infancy. FM periodicity also predicts temperament, but in the opposite direction of FM counts. That is, a larger number of changes between quiescence and activity is associated with being more predictable, more adaptable, less dull, and less difficult as infants, indicating that measures of FM may be assessing processes involved with regulation (DiPietro et al., 1996b). This relation is important in a number of ways. First, it is the only comparison to date between the patterning of FM and postnatal variables. Second, it demonstrates that aspects of the pattern of FM are related to postnatal development, and third, that these relations are different from those of FM counts and infant variables. Clearly, this finding demonstrates that more exploration of the associations of FM pattern and postnatal development is necessary.
To date, DiPietro et al. (1996b) are the only researchers that examine the relation between FM and infant temperament. Though it is an important start, more research is needed to fully explicate the association between FM and infant temperament. If FM and infant temperament dimensions are related, then certain assumptions about temperament development (i.e., temperament shows temporal stability) will be further supported (DiPietro et al., 1996b).
FM and Mental and Motor Development
Continuity between specific FM has been observed across birth (Prechtl, 1987). This continuity lasts until around two months after birth, at which point it seems as though the infant goes through an extreme change in behavioral organization. Additionally, mother-felt FM in late pregnancy (36 to 38 weeks gestation) predicts neonatal performance (2-4 weeks postnatal) on an orientation-animate visual measure (Ishikawa & Minamide, 1984).
FM also predicts mental and motor development beyond the neonatal period. The total number of movements in the 7th, 8th, 9th, and 10th months of gestation were positively associated with mental and motor development at 3, 6, 9, and 12 months postnatal, with correlations ranging from .24 to .84 (Richards & Newbery, 1938; Walters, 1965). When FM was examined as it predicts mental and motor development later on in infancy at 1 and 2 years, a different type of relation emerged. The total amount of time the fetus moves in a 50-minute period is related to lower levels of locomotor capability (can the infant sit, crawl, stand, or walk; DiPietro et al., 2002).
Thus, there are hints of links between FM and motor development, but more research is needed to fully understand them so that it may become possible to detect potentially abnormal infant development during the fetal period, allowing for earlier intervention. FM, as measured at specific time points in gestation, has been associated with a number of postnatal characteristics, as demonstrated in this review. However, it remains unclear exactly how the temporal development of FM, and its patterning, may affect how it is related to postnatal development.
Need to Consider the Developmental Function of FM
The reviewed research has generally made use of FM measured at single time points (e.g., DiPietro et al., 1996b; DiPietro et al., 2002) or mean FM averaged across time (e.g., Ishikawa & Minamide, 1984) and has ignored the DF when considering FM and outcome. However, the DF is an important aspect of behavioral development (McCall, 1990; Wohlwill, 1973), because the DF, rather than the mean, describes the actual course of development and provides a time-course for emerging behaviors and skills. DF may be independent from mean performance and, as a consequence, may explain aspects of development not accounted for by mean performance. Showing how individuals vary in their pattern of development over time, then may explain development in ways that are not possible by traditional mean analyses. Therefore, DF may also be an informative approach to studying fetal behaviors and linking fetal behaviors to postnatal development.
Summary
Both the development of FM and how FM counts relate to maternal and infant variables have been studied extensively. FM, on average, increases through the 28th week of pregnancy and then begins to decrease in incidence, though there is considerable variability to this pattern (Richards et al., 1938; Edwards & Edwards, 1970; Eaton & Saudino, 1992). FM shows some continuity across birth, with FM counts predicting infant activity (Almli et al., 2001; Groome et al., 1999; DiPietro et al., 1996b; DiPietro et al., 2002), other dimensions of infant temperament (DiPietro et al., 1996b), and infant mental and motor development (Richards & Newbery, 1938; Walters et al., 1965; DiPietro et al., 2002). FM also is an indicator of overall fetal neurological well-being and low levels of FM have been associated with fetal distress (Prechtl & Einspieler, 1997).
However, there is still much to be done to coalesce the existing research on FM. Much of the research is divided into descriptions of FM, either in the form of summary scores or as developmental patterns; properties of FM; or its behavioral correlates. The research associating FM with infant behavior uses individual FM counts taken at varying points throughout the third trimester and has ignored individual variation in developmental patterns. There is much information that has yet to be obtained from examination of individual developmental patterns of FM. Evidence has been provided of stable individual differences in FM pattern over the last trimester (Eaton & Saudino, 1992), and this variability in the DF of FM has never been studied in relation to infant behavior. Because individual differences and DF can both operate in behavioral development and may each be influenced by different factors or result in different outcomes (McCall, 1990), studying the DF of FM in detail and as it relates to maternal and infant behavior may provide answers we do not currently know to questions about fetal and infant development, in addition to answering questions that are not possible to address by only looking at mean performance or individual FM counts.
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