The development of ultradian rhythms in the human fetus

Fetal behavior and gestational serotonin reuptake inhibitor exposure: relationships between behavior, drug dosage, plasma drug level, and a measure of drug bioeffect

Determination of the relationships between drug dosage, maternal and infant (cord blood) plasma drug concentrations, and serotonin reuptake inhibitor (SRI) bioeffect on offspring neurobehavior is crucial to assessing the effects of gestational SRI exposure. Measurement of maternal and cord blood platelet serotonin (5-HT) provides an index of inhibitory bioeffect at the 5-HT transporter and complements other measures of drug exposure. Three groups of mother-infant pairs were evaluated: (1) mothers with depression untreated with SRIs (DEP, n = 17), (2) mothers treated for depression with SRIs (DEP + SRI, n = 17), and (3) mothers who were not depressed and untreated (ND, n = 29). Fetal movement was assessed using a standardized ultrasound imaging and rating protocol. Maternal and cord blood platelet 5-HT levels were obtained from all participants. For the SRI + DEP group, maternal and infant plasma drug concentrations and an estimate of third-trimester maternal SRI drug exposure were obtained. As expected, substantially lower median platelet 5-HT levels were observed in the DEP + SRI group than in the non-exposed, combined ND and DEP groups. In non-exposed mothers and infants, platelet 5-HT levels were not affected by the presence of maternal depression. Lower maternal and infant platelet 5-HT levels were associated with more immature fetal movement quality. Although these data are limited by small sample size, the bioeffect index of in vivo platelet 5-HT transporter inhibition appears to provide a valuable approach for elucidating and possibly predicting the effects of gestational SRI exposure on fetal and perinatal neurobehavior.

Towards better reliability in fetal heart rate variability using time domain and spectral domain analyses. A new method for assessing fetal neurological state?

OBJECTIVES

Fetal heart rate variability (FHRV) has shown potential in fetal surveillance. Therefore, we aimed to evaluate the reliability of time domain and spectral domain parameters based on non-invasive fetal electrocardiography (NI-FECG).

METHOD

NI-FECG, with a sampling frequency of 1 kHz, was obtained in 75 healthy, singleton pregnant women between gestational age (GA) 20+0 to 41+0. The recording was divided into a) heart rate pattern (HRP) and b) periods fulfilling certain criteria of stationarity of RR-intervals, termed stationary heart rate pattern (SHRP). Within each recording, the first and the last time series from each HRP with less than 5% artifact correction were analyzed and compared. Standard deviation of normal-to-normal RR-intervals (SDNN), root mean square of successive differences (RMSSD), high frequency power (HF-power), low frequency power (LF-power), and LF-power/HF-power were performed. A multivariate mixed model was used and acceptable reliability was defined as intraclass correlation coefficient (ICC) ≥ 0.80 and a coefficient of variation (CV) ≤ 15%. Based on these results, the CV and ICC were computed if the average of two to six time series was used.

RESULTS

For GA 28+0 to 34+6, SDNN and RMSSD exhibited acceptable reliability (CV < 15%; ICC > 90%), whereas GA 35+0 to 41+0and 20+0 to 27+6 showed higher CVs. Spectral domain parameters also showed high CVs However, by using the mean value of two to six time series, acceptable reliability in SDNN, RMSSD and HF-power from GA 28+0 was achieved. Stationarity of RR-intervals showed high influence on reliability and SHRP was superior to HRP, whereas the length of the time series showed minor influence.

CONCLUSION

Acceptable reliability seems achievable in SDNN, RMSSD and HF-power from gestational week 28. However, stationarity of RR-intervals should be considered when selecting time series for analyses.

Fetal respiratory movements improve reliability of heart rate variability and suggest a coupling between fetal respiratory arrhythmia and vagal activity

Fetal heart rate variability (FHRV) reflects autonomic cardiac regulation. The autonomic nervous system constantly adjusts the heart rate to maintain homeostasis. By providing insight into the fetal autonomic state, FHRV has the potential to become an investigational and clinical instrument. However, the method needs standardization and the influence of fetal movements, including fetal respiratory movements, is not well explored. Therefore, in a highly standardized setting, the aim was to evaluate the association between fetal movements and fetal heart rate variability (FHRV) including their impact on reliability. Fetal heart rate was obtained by noninvasive fetal electrocardiography (NI-FECG) and fetal movements by simultaneous ultrasound scanning in 30 healthy singleton pregnant women on two occasions with a maximum interval of 7 days. The standard deviation of normal-to-normal RR-intervals (SDNN), root mean square of successive RR-interval differences (RMDDS), high-frequency power (HF-power), low-frequency power (LF-power), and LF/HF were measured. A multivariate mixed model was used and reliability was defined as acceptable by a coefficient of variance (CV) ≤15% and an intraclass correlation coefficient (ICC) ≥0.80. During time periods with fetal respiratory movements, the highest reliability was achieved. Intra- and inter-observer reliability measurements were very high (CV: 0-9%; ICC ≧ 0.86). Within the same recording, SDNN and RMSSD achieved acceptable reliability (CV: 14-15%; ICC ≧ 0.80). However, day-to-day reliability displayed high CV's. In time periods with fetal respiratory movements, as compared to periods with quiescence RMSSD and HF-power were higher (Ratio: 1.33-2.03) and LF/HF power lower (Ratio: 0.54). In periods with fetal body movements SDNN, RMSSD and HF-power were higher (Ratio: 1.27-1.65). In conclusion, time periods with fetal respiratory movements were associated with high reliability of FHRV analyses and the highest values of parameters supposed to represent vagal activity.

Maternal smoking in pregnancy, fetal activity & newborn behavioral state: An observational ultrasound study

Maternal smoking during pregnancy (MSDP) remains one of the most common prenatal drug exposures in the US and worldwide. MSDP is associated with medical risk for the fetus and altered behavioral development in infants; however, fewer studies have examined the impact of MSDP on fetal behavior or newborn behavioral state. We investigated associations between MSDP and (a) fetal motor activity and (b) newborn behavioral state following handling. Participants were 79 healthy mother-fetus/newborn pairs (57% MSDP-exposed). MSDP was measured by maternal interview and verified by saliva biomarkers. Mothers completed an observational fetal ultrasound assessment between 24 and 37 weeks gestation (M = 28 weeks), including baseline, vibro-acoustic stimulus and recovery periods. Total fetal motor activity and complex body movements were coded from ultrasound videos. Following delivery, newborn post-handling behavioral state was assessed by direct observational coding. MSDP exposure was associated with higher baseline fetal motor activity, particularly at younger gestational ages. Further, motor reactivity to stimulation emerged at later gestational ages in MSDP-exposed fetuses, while motor reactivity was consistent across gestational ages in unexposed fetuses. Finally, heavy MSDP exposure was associated with more arousal following handling and greater need for soothing interventions in the newborn period. Monitoring of fetal behavior via ultrasound may offer a unique opportunity to identify at-risk infants and provides data for stronger public health messaging regarding risks of MSDP. Associations between MSDP and increased newborn fussiness highlight opportunities for education and anticipatory guidance in the postpartum period.

A diurnal fetal movement pattern: Findings from a cross-sectional study of maternally perceived fetal movements in the third trimester of pregnancy

BACKGROUND AND OBJECTIVES

Encouraging awareness of fetal movements is a common strategy used to prevent stillbirths. Information provided to pregnant women about fetal movements is inconsistent perhaps due to limited knowledge about normal fetal movement patterns in healthy pregnancies. We aimed to describe maternally perceived fetal movement strength, frequency, and pattern in late pregnancy in women with subsequent normal outcomes.

METHODS

Participants were ≥28 weeks' gestation, with a non-anomalous, singleton pregnancy who had been randomly selected from hospital booking lists and had consented to participate. Fetal movement data was gathered during pregnancy via a questionnaire administered face-to-face by research midwives. Participants remained eligible for the study if they subsequently gave birth to a live, appropriate-for-gestational-age baby at ≥37 weeks.

RESULTS

Participants were 274 women, with normal pregnancy outcomes. The majority (59.3%, n = 162) of women reported during antenatal interview that the strength of fetal movements had increased in the preceding two weeks. Strong fetal movements were felt by most women in the evening (72.8%, n = 195) and at night-time including bedtime (74.5%, n = 199). The perception of fetal hiccups was also reported by most women (78.8%). Women were more likely to perceive moderate or strong fetal movements when sitting quietly compared with other activities such as having a cold drink or eating.

CONCLUSIONS

Our data support informing women in the third trimester that as pregnancy advances it is normal to perceive increasingly strong movement, episodes of movements that are more vigorous than usual, fetal hiccups, and a diurnal pattern involving strong fetal movement in the evening. This information may help pregnant women to better characterise normal fetal movement and appropriately seek review when concerned about fetal movements. Care providers should be responsive to concerns about decreased fetal movements in the evening, as this is unusual.

Counting fetal movements of small-for-gestational infants using a fetal movement acceleration measurement recorder

Background: Our purpose was to clarify whether small-for-gestational (SGA) infants is associated with a decrease in fetal movements (FMs) even in the absence of hypoxia. We used a fetal movement acceleration measurement (FMAM) recorder, which enabled counting gross FMs for hours at a time.Methods: (1) Parameters of FMs for 13 women who delivered SGA infants were plotted over normal reference value curves made from 64 normal pregnant women in another study. (2) Linear regression analysis was conducted for the women with SGA infants and the normal pregnant women.Results: Thirty-eight data recordings were available in the SGA group. (1) For the ratio of movement positive 10-s epoch, 14 recordings (36.8%) were below 10% of the normal values. For an average number of movements, 13 (34.2%) were below 10%. Regarding average number, average duration, and longest duration of non-movement period, 12 (31.6%), 13 (34.2%), and 15 records (39.4%) were above 90% of the normal values, respectively. (2) SGA was a factor that decreased the positive epoch ratio and the average movements number, and increased the average number and duration, and the longest duration of non-movement period.Conclusions: SGA is associated with decreased movements even in the absence of hypoxia.

Impact of maternal prenatal smoking on fetal to infant neurobehavioral development

Despite recent emphasis on the profound importance of the fetal environment in "programming" postnatal development, measurement of offspring development typically begins after birth. Using a novel coding strategy combining direct fetal observation via ultrasound and actocardiography, we investigated the impact of maternal smoking during pregnancy (MSDP) on fetal neurobehavior; we also investigated links between fetal and infant neurobehavior. Participants were 90 pregnant mothers and their infants (52 MSDP-exposed; 51% minorities; ages 18-40). Fetal neurobehavior at baseline and in response to vibro-acoustic stimulus was assessed via ultrasound and actocardiography at M = 35 weeks gestation and coded via the Fetal Neurobehavioral Assessment System (FENS). After delivery, the NICU Network Neurobehavioral Scale was administered up to seven times over the first postnatal month. MSDP was associated with increased fetal activity and fetal limb movements. Fetal activity, complex body movements, and cardiac-somatic coupling were associated with infants' ability to attend to stimuli and to self-regulate over the first postnatal month. Furthermore, differential associations emerged by MSDP group between fetal activity, complex body movements, quality of movement, and coupling, and infant attention and self-regulation. The present study adds to a growing literature establishing the validity of fetal neurobehavioral measures in elucidating fetal programming pathways.

Maternal perception of fetal movements in the third trimester: A qualitative description

PROBLEM

Decreased fetal movements is a common reason for unscheduled antenatal assessment and is associated with adverse pregnancy outcome.

BACKGROUND

Fetal movement counting has not been proven to reduce stillbirths in high-quality studies.

AIMS

The aim was to explore a qualitative account of fetal movements in the third trimester as perceived by pregnant women themselves.

METHODS

Using qualitative descriptive methodology, interviews were conducted with 19 women experiencing an uncomplicated first pregnancy, at two timepoints in their third trimester. Interview transcripts were later analysed using qualitative content analysis.

FINDINGS

Pregnant women described a sustained increase in strength, frequency and variation in types of fetal movements from quickening until 28-32 weeks. Patterns of fetal movement were consistently described as involving increased movement later in the day and as having an inverse relationship to the women's own activity and rest. At term, the most notable feature was increased strength. Kicking and jolting movements decreased whilst pushing and rolling movements increased.

DISCUSSION

Maternal descriptions of fetal activity in this study were consistent with other qualitative studies and with ultrasound studies of fetal development.

CONCLUSION

Pregnant women observe a complex range of fetal movement patterns, actions and responses that are likely to be consistent with normal development. Maternal perception of a qualitative change in fetal movements may be clinically important and should take precedence over any numeric definition of decreased fetal movement. Midwives may inform women that it is normal to perceive more fetal movement in the evening and increasingly strong movements as pregnancy advances.

Maternal and Early-Life Circadian Disruption Have Long-Lasting Negative Consequences on Offspring Development and Adult Behavior in Mice

Modern life involves chronic circadian disruption through artificial light and these disruptions are associated with numerous mental and physical health maladies. Because the developing nervous system is particularly vulnerable to perturbation, we hypothesized that early-life circadian disruption would negatively impact offspring development and adult function. Pregnant mice were subjected to chronic circadian disruption from the time of uterine implantation through weaning. To dissociate in utero from postnatal effects, a subset of litters was cross-fostered at birth from disrupted dams to control dams and vice versa. Postnatal circadian disruption was associated with reduced adult body mass, social avoidance, and hyperactivity. In utero disruption resulted in more pronounced social avoidance and hyperactivity, phenotypes not abrogated by cross-fostering to control mothers. To examine whether circadian disruption affects development by acting as an early life stressor, we examined birthweight, litter size, maternal cannibalism, and epigenetic modifications. None of these variables differed between control and disrupted dams, or resembled patterns seen following early-life stress. Our findings indicate that developmental chronic circadian disruption permanently affects somatic and behavioral development in a stage-of-life-dependent manner, independent of early life stress mechanisms, underscoring the importance of temporal structure during development, both in utero and early postnatal life.

Fetal response to maternal hunger and satiation - novel finding from a qualitative descriptive study of maternal perception of fetal movements

Background

Maternal perception of decreased fetal movements is a specific indicator of fetal compromise, notably in the context of poor fetal growth. There is currently no agreed numerical definition of decreased fetal movements, with the subjective perception of a decrease on the part of the mother being the most significant definition clinically. Both qualitative and quantitative aspects of fetal activity may be important in identifying the compromised fetus. Yet, how pregnant women perceive and describe fetal activity is under-investigated by qualitative means. The aim of this study was to explore normal fetal activity, through first-hand descriptive accounts by pregnant women.

Methods

Using qualitative descriptive methodology, interviews were conducted with 19 low-risk women experiencing their first pregnancy, at two timepoints in their third trimester. Interview transcripts were later analysed using qualitative content analysis and patterns of fetal activity identified were then considered along-side the characteristics of the women and their birth outcomes.

Results

This paper focuses on a novel finding; the description by pregnant women of fetal behaviour indicative of hunger and satiation. Full findings will be presented in later papers. Most participants (74% 14 of 19) indicated mealtimes were a time of increased fetal activity. Eight participants provided detailed descriptions of increased activity around meals, with seven (37% 7 of 19) of these specifying increased fetal activity prior to meals or in the context of their own hunger. These movements were interpreted as a fetal demand for food often prompting the mother to eat. Interestingly, the women who described increased fetal activity in the context of hunger subsequently gave birth to smaller infants (mean difference 364 gm) than those who did not describe a fetal response to hunger.

Conclusions

Food seeking behaviour may have a pre-birth origin. Maternal-fetal interaction around mealtimes could constitute an endocrine mediated communication, in the interests of maintaining optimal intrauterine conditions. Further research is warranted to explore this phenomenon and the potential influence of feeding on the temporal organisation of fetal activity in relation to growth.

Fetal movement counting at home with a fetal movement acceleration measurement recorder: a preliminary report

OBJECTIVE

Fetal Movement Acceleration Measurement (FMAM) recorder was developed to facilitate gross fetal movement counting. The aim was to assess its reliability.

METHODS

Using the recorder, six pregnant women recorded fetal movements by themselves when they slept at their home weekly from 30 weeks to term. The recorder has 2 acceleration sensors; 1 for fetal movement (FM sensor) and another for maternal movement (MM sensor). Before sleeping, each subject attached the FM sensor to her abdomen, and the MM sensor to her thigh. All the recorded data were divided into 10-sec epochs, and presence of fetal movements was judged for all epochs (total epoch). The epoch was judged as positive for movement (positive epoch) when the FM sensor detected abdominal wall oscillations and the MM sensor did not detect maternal movements. The percentage of positive epoch number to total epoch and the maximum consecutive negative epoch number was calculated.

RESULTS

The mean percentage was approximately 20-25% at 30-34 weeks and 10-15% at 35-38 weeks. The negative epoch number linearly increased after approximately 33-34 weeks of gestation.

CONCLUSIONS

The FMAM recorder was reliable for long-duration recording of gross fetal movements at home.

Fetal effects of psychoactive drugs

Psychoactive drug use by pregnant women has the potential to effect fetal development; the effects are often thought to be drug-specific and gestational age dependent. This article describes the effects of three drugs with similar molecular targets that involve monoaminergic transmitter systems: cocaine, methamphetamine, and selective serotonin re-uptake inhibitors (SSRIs) used to treat maternal depression during pregnancy. We propose a possible common epigenetic mechanism for their potential effects on the developing child. We suggest that exposure to these substances acts as a stressor that affects fetal programming, disrupts fetal placental monoamine transporter expression and alters neuroendocrine and neurotransmitter system development. We also discuss neurobehavioral techniques that may be useful in the early detection of the effects of in utero drug exposure.

Parent-infant synchrony and the construction of shared timing; physiological precursors, developmental outcomes, and risk conditions

Synchrony, a construct used across multiple fields to denote the temporal relationship between events, is applied to the study of parent-infant interactions and suggested as a model for intersubjectivity. Three types of timed relationships between the parent and child's affective behavior are assessed: concurrent, sequential, and organized in an ongoing patterned format, and the development of each is charted across the first year. Viewed as a formative experience for the maturation of the social brain, synchrony impacts the development of self-regulation, symbol use, and empathy across childhood and adolescence. Different patterns of synchrony with mother, father, and the family and across cultures describe relationship-specific modes of coordination. The capacity to engage in temporally-matched interactions is based on physiological mechanisms, in particular oscillator systems, such as the biological clock and cardiac pacemaker, and attachment-related hormones, such as oxytocin. Specific patterns of synchrony are described in a range of child-, parent- and context-related risk conditions, pointing to its ecological relevance and usefulness for the study of developmental psychopathology. A perspective that underscores the organization of discrete relational behaviors into emergent patterns and considers time a central parameter of emotion and communication systems may be useful to the study of interpersonal intimacy and its potential for personal transformation across the lifespan.

Normal fetal motility: an overview

After 35 years of real-time two-dimensional sonography, and now that 4D sonography is within our grasp, this article presents an overview of present-day knowledge of normal fetal motility. A literature search was carried out on articles from 1970, using the keywords: 'fetal', 'movements', 'motility', 'movement patterns', 'ultrasound' and 'sonography'. Inclusion criteria were human studies and use of real-time sonography. Articles were screened for type of motor assessment procedure, in terms of whether they: specified movements for participating body parts (specific movement pattern, SMP), were qualitative (performance in terms of speed and amplitude), were quantitative, identified behavioral states, stated the duration of observation, and specified gestational age. We noted developmental milestones obtained for each study aim. One of four aims was identified for each article, depending on whether it focused on emergence, development, or continuity after birth of the movement patterns, or on the relationship of various motor aspects to other parameters that evaluate fetal condition, such as blood flow and fetal heart rate. A total of 109 relevant articles was identified, examining 9862 fetuses. Assessment was performed primarily with analysis of SMPs (89%); 52% also included non-SMPs (NSMPs), 78% included quantification, 24% assessment of quality, and 32% behavioral states. The duration of observation was 1 h or longer in 50% of the studies. The focus in 28 studies was on emergence, in 44 it was on development, in five it was on continuity and in 32 it was on relationship of the movements with other parameters of fetal well-being. A few milestones identified were determination of the strictly age-related emergence of SMPs and behavioral states, the highly reproducible quality of SMPs throughout gestation, the age-related trends in quantified SMPs, the continuity in quality and quantity after birth, and the close relationship between motility and heart-rate variability, flow parameters, and behavioral states. Periods of longest inactivity recorded before 20 weeks were 13 min; after 30 weeks they were 45 min. Much insight was obtained into the development of motility and its relationship to other parameters from those articles applying comparable assessment procedures. An assessment procedure with well-defined SMPs, qualitative and quantitative aspects of SMPs and NSMPs, and an observation period dependent on age are advocated for future research.

From biological rhythms to social rhythms: Physiological precursors of mother-infant synchrony

Links between neonatal biological rhythms and the emergence of interaction rhythms were examined in 3 groups (N = 71): high-risk preterms (HR; birth weight <1,000 g), low-risk preterms (LR; birth weight =1,700-1,850 g), and full-term (FT) infants. Once a week for premature infants and on the 2nd day for FT infants, sleep-wake cyclicity was extracted from 4-hr observations and cardiac vagal tone was measured. At term age, infant orientation was tested with the Neonatal Behavior Assessment Scale. At 3 months, arousal modulation and emotion regulation were assessed, and mother-infant synchrony was computed from microanalysis of face-to-face interactions using time-series analysis. Sleep-wake amplitudes showed a developmental leap at 31 weeks gestation, followed by a shift in vagal tone at 34 weeks gestation. At term, differences among FT, LR, and HR infants were observed for biological rhythms in a linear-decline pattern. Sleep-wake cyclicity, vagal tone, newborn orientation, and arousal modulation were each uniquely predictive of mother-infant synchrony. The organization of physiological oscillators appears to lay the foundation for the infant's capacity to partake in a temporally matched social dialogue.

Neurobehavioral assessment from fetus to infant: the NICU Network Neurobehavioral Scale and the Fetal Neurobehavior Coding Scale

This review provides an overview and definition of the concept of neurobehavior in human development. Two neurobehavioral assessments used by the authors in current fetal and infant research are discussed: the NICU Network Neurobehavioral Assessment Scale and the Fetal Neurobehavior Coding System. This review will present how the two assessments attempt to measure similar processes from pre to post-natal life by examining three main components of neurobehavior: neurological, behavioral and stress/reactivity measures. Assessment descriptions, strengths and weaknesses, as well as cautions and limitations are provided.

Longitudinal study of fetal body movements: nomograms, intrafetal consistency, and relationship with episodes of heart rate patterns a and B

Our objective was to investigate the longitudinal development of incidence parameters of fetal body movements to define normal reference ranges, to relate them to episodes of fetal heart rate patterns A and B, and to determine the intrafetal consistency for these parameters. Twenty-nine fetuses were studied longitudinally from 24 wk of gestation. Fetal body movements and heart rate were recorded at fortnightly intervals between 24 and 36 wk of gestation and weekly from 36 wk of gestation. Data were analyzed using multilevel analysis. Reference ranges were constructed for the percentage of observation time that movements were present, the number of movement bursts per hour, the mean burst duration, and the median onset-onset interval. The median percentage incidence of fetal body movements decreased from 17% at 24 wk to about 7% near term. The developmental course was the same during active episodes. Body movements also decreased during episodes of relative quiescence, in the course of pregnancy. Intrafetal variance was on average 40-80% of the total range of the four movement parameters. Normal reference ranges were developed for incidence parameters of fetal body movements from 24 wk of gestation onward. The overall decline in the incidence of movements during pregnancy appeared to be a developmental phenomenon and not due to progressively increasing episodes of fetal quiescence. Individual fetuses showed a degree of consistency in the percentage incidence of body movements, but intra- and interfetal variances were generally high, resulting in wide ranges.

Human fetal and neonatal movement patterns: Gender differences and fetal-to-neonatal continuity

Longitudinal quantification of leg movements per minute for human subjects during both fetal and neonatal periods was accomplished from videotapings conducted antenatally (ultrasonography 30, 34, and 37 weeks gestational age) and postnatally (birth and 6 weeks of age). Fetal/neonatal subjects displayed decreasing numbers of leg movements per minute during antenatal development (30 to 37 weeks), followed by increasing numbers of leg movements per minute during postnatal development (birth to 6 weeks of age). Male subjects displayed greater numbers of leg movements per minute than female subjects during both antenatal and postnatal development. Fetal-to-neonatal continuity for numbers of leg movements per minute was found for comparisons between fetal (37 weeks gestational age) and neonatal (during sleep states at birth) measures, and females displayed a stronger and different movement continuity pattern than males. These results indicate a differential time course for neurobehavioral development of male and female fetuses/neonates, and the findings have implications for the clinical assessment of fetal neurobehavioral development and well-being.

Temporal organization of fetal behavior from 24-weeks gestation onwards in normal and complicated pregnancies

Developmental aspects of behavioral organization were investigated in 29 healthy fetuses from 24-weeks gestation onwards: (a) short-term association between body (GM) and eye (EM) movements; (b) linkage of pairs of the three state variables [fetal heart rate pattern (FHRP), GM, and EM]; and (c) sequence of change of state variables during transitions. Linkage and sequence were also studied in complicated pregnancies. Short-term association between GM and EM was well established after 28 weeks. Linkage of state variables improved considerably after 32-34 weeks. FHRP was the first variable to change during synchronized transitions from 1F to 2F between 28-39 weeks, and the last variable during 2F to 1F transitions between 32-39 weeks. Although clear developmental patterns could be recognized, the interfetal variability was such that identification of the abnormal fetus is still difficult. Only transitions were significantly different in growth-restricted fetuses, as they showed no specific sequence of change. Assessing the temporal organization of fetal behavior seems, therefore, until now, not of great clinical value.