The Eyes Have It: Fetal Reactions To Sound And Light Stimulation And Maternal Mental Health

It is known that fetuses blink spontaneously in the womb (e.g. Petrikovsky et al 2003) and that eye-blink rate is related to the age of the fetus or baby. Given that eye-blink rate is widely used postnatally to assess cognitive performance (e.g. Paprocky & Lenski 2017), we can use eye blink to assess fetal reactions to experimental stimulation.

In addition, it is agreed that maternal anxiety and depression affect fetal neurodevelopment (Glover, 2014 ) with a significantly increased risk after birth for neurodevelopmental disorders such as increased risk for ADHD (e.g. van den Bergh & Marcoen, 2004) and emotional and behavioral problems in childhood (e.g. Leis, Heron & Stuart 2013; Giallo, Woodhouse, Gartland, Hiscock & Brown, 2015). In particular, stressful conditions are associated with increased eye-blink behavior (Huggenberger et al, 2011). Descroiz et al (2015) reported that premature infants between 27 and 34 weeks at birth blinked more frequently than fetuses of the same gestational age. This result may be due to exposure to the NICU environment resulting in increased stress among premature infants.

Fig 1 Example of opening and closing of eyes by a fetus 32 weeks gestation. Figure courtesy Nadja Reissland.

Although perinatal effects of maternal mental health are increasingly investigated (e.g. Glover, 2014), the effects of the maternal mental state on the prenatal behavioral profile as observed in 4D ultrasound recordings are less well researched. Therefore, in order to assess the effects of cross-modal sound and light stimulation on the fetus controlling for maternal health, the current study (Reissland, et al 2018) observed the effects of maternal anxiety and depression, as well as maternal self-reported stress on fetal eye-blink rate in response to externally administered cross-modal sound and light stimulation.

Study Design

To assess fetal reaction to sound and light stimulation, we compared the behavioral profile of a control group of 14 fetuses who were not subjected to light and sound stimulation, with the behavioral profile of an experimental group of 21 fetuses who had been exposed to light and sound stimulation. Both groups were assessed at 32 weeks gestational age. Given that maternal mental state affects the fetal behavioural profile (e.g. Reissland et al, 2018; Reissland et al 2015) we controlled for maternal anxiety, depression, and stress by assessing maternal anxiety and depression with the Hospital Anxiety and Depression Scale (HADS, Zigmond & Snaith 1983) and stress with the Perceived Stress Scale (PSS; Cohen, Kamarck & Mermelstein, 1983).

Results

Results indicated that fetuses exposed to sound and light stimulation habituated to that stimulation. Stimuli (“Ma,” “Me,” “Mo,” & white noise with and without light; see Reissland et al, 2018 for detailed descriptions of the stimuli) were applied four times in a random order. The results indicated that following exposure to the sound and light stimuli, fetuses showed a reduction in eye-blink reactions. In fact, they reduced their eye blink reaction by half after having been exposed to three of the stimuli. This resulted in a significantly reduced reaction to the fourth experimental stimulation presentation. Hence, it appears that while fetuses do not differentiate between the four different sounds (“Ma,” “Me,” “Mo,” and white noise) with and without light stimulation, fetuses do habituate to or “remember” the stimulation and therefore react with a reduction in eye-blink frequency after repeated exposure.

An analysis of maternal mental state indicated that fetuses of mothers with increased levels of anxiety showed increased eye-blink rates in response to sound stimulation, but that light stimulation did not affect fetal blink rate. In contrast, increased levels of maternal depression affected fetal blink rate in response to sound, but not light stimulation by reducing it significantly. For each unit increase of depression, measured using the Hospital Anxiety and Depression Scale (Zigmond & Snaith 1983) fetuses decreased their eye blink rate by 21%.

Conclusion

The results indicate that fetuses at 32 weeks gestation are sensitive to maternal mental state, specifically anxiety and depression and that fetal reactions to sound stimulation vary depending on maternal reports of anxiety and depression. Future studies using eye blink as a measure for fetal reaction (pre-cognition) must control for maternal anxiety and depression given that fetal responses vary depending on not only the external stimulus applied but also maternal emotional state.

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