Sex differences in fetal habituation

Abstract

There is some evidence for sex differences in habituation in the human fetus, but it is unknown whether this is due to differences in central processing (habituation) or in more peripheral processes, sensory or motor, involved in the response. This study examined whether the sex of the fetus influenced auditory habituation at 33 weeks of gestation, and whether this was due to differences in habituation or in the sensory or motor components using a set of four experiments. The first experiment found that female fetuses required significantly fewer stimulus presentations to habituate than males. The second experiment revealed no difference in the spontaneous motor behaviour of male and female fetuses. The third experiment examined auditory intensity thresholds for the stimuli used to habituate the fetus. No differences in thresholds were found between males and females, although there was inter-individual variability in thresholds. A final experiment, using stimuli individualized for that particular fetus' auditory intensity threshold, found that female fetuses habituated faster than males. In combination, the studies reveal that habituation in the human fetus is affected by sex and this is due to a difference in central 'information processing' of the stimuli rather than peripheral aspects of the response. It is argued that male and female fetuses present different neurobehavioural developmental trajectories, with females more advanced at 33 weeks than males. This study suggests that research examining prenatal behaviour should consider the factor of fetal sex. This may be particularly pertinent where there is an intention to use the results diagnostically.

Physiological reactivity of pregnant women to evoked fetal startle

“…As such, this can be regarded as indicative of a less well-regulated response earlier in gestation, as opposed to a more self-limiting motor reaction near term. We did not observe a sex difference in fetal reactivity at either gestational age as has been reported in one study [40] but not in another [49]. The presence or absence of sex differences in fetal responses to stimulation awaits confirmation by additional research with larger samples.…”

“…Thus, airborne auditory signals delivered above and not touching the maternal abdomen tend to elicit a less intense response, but are necessary to a design in which pregnant women must be blind to stimulus presentation. Airborne stimuli shown to elicit a fetal response include electronically generated signals of varying intensity and frequency [46–49], speech sounds [50–52], and music [37, 53]. …”

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“…Commencing at 31 weeks gestation, male fetuses reacted with greater increases in fetal heart rate to a startling stimulus than female fetuses and, whereas the males’ recovery curve following stimulation continued to lessen through term, the female regulatory response was mature by 31 weeks (Buss et al, 2009). As compared to male fetuses, female fetuses require fewer trials to habituate to vibroacoustic stimuli (Hepper, 2012; McCorry & Hepper, 2007), display the capacity to habituate earlier in gestation (Leader, Baillie, Martin, & Vermeulen, 1982a), and show faster improvement in habituation performance from 31 to 35 weeks gestation (McCorry & Hepper, 2007). The ability to habituate connotes information processing capacity and as such, this convergent evidence suggests accelerated neuromaturation in female fetuses.…”

“…Male fetuses were more active than female fetuses in our initial small cohort (DiPietro et al, 1996b) but not in later ones (DiPietro, Caulfield, et al, 2004; DiPietro et al, 1998; DiPietro et al, 2009; DiPietro et al, 2010). Ultrasound observations of motor activity have also not generated observation of sex differences (deVries, Visser, & Prechtl, 1988; Hepper, 2012) although there is one report that male fetuses make more leg movements (Almli et al, 2001). There is a single report that male fetuses move more often at term but not before (Robles de Medina, Visser, Huizink, Buitelaar, & Mulder, 2003).…”

From early markers to neuro-developmental mechanisms of autism

“…Given the likely involvement of pre-natal and post-natal synaptic functioning in the etiology of this disorder, neural atypicalities and their phenotypic markers might be measurable at younger ages, and potentially even before birth. Behavioral measures of fetal sensory reactivity (Hepper, Dornan, & Lynch, 2012) and in utero brain imaging methods (Habas et al, 2012) provide possibilities for investigating autism even earlier during development. Some of the identified post-natal markers for autism that are now proposed as primary causes for this disorder, may turn out to be secondary effects of transitory pre-natal neural impairments (Johnson et al, in press).…”