Stress is a compound term that includes a large number of emotional states such as mild stress, anxiety and depression. During gestation, it can be experienced by pregnant women as prenatal stress, anxiety and antenatal depression. and it may have negative effects on the development of the fetus and child. In this paper, maternal stress identified and evaluated through animal and human studies in order to clarify the main risk arising for the fetus and child. Pathways by which pregnant mother’s emotional states may affect the foetus are also described.
The main risks arising to the fetus/child due to prenatal stress, anxiety and antenatal depression.
Stress is a part of humans’ life and a normal reaction to stressful situations. It is a chemical reaction in human’s brain and body due to “fight or flight” response and is intended to help people surviving. However, intense and prolonged stress may convey risks for anxiety and depressive disorders (Judah, Grant, Mills, Lechner, Slish, Davidson, & Wingate, 2013).
Stress, anxiety and depression are characterized by high comorbidity and a strong association between them. Defining these briefly, stress is linked to persistent irritability, tension and a tendency to become easily frustrated or upset. Anxiety is characterized by a physiological hyperstimulation and a mixture of general distress as agitation, irritability, impatience and difficulty relaxing and depression refers to low levels of positive affectivity, e.g. prolonged despair, dysphoria, lack of self-esteem, reduced encouragement, hopelessness, anhedonia and lack of energy (Wenzel, 2011).
According to the World Health Organization (WHO, 2011). one of the most prevalent factors of emergence of stress, anxiety and depression symptoms in women is pregnancy mainly because of intense changes that occur in pregnant physiology during this period. However, stress as a generic term includes depression and anxiety and high levels of comorbidity between stress, anxiety and depression have raised many questions about the validity of current diagnostic criteria (Judah et al., 2013). especially concerning the occurrence of these symptoms during pregnancy. This is due to the limited research on the association between mother’s mood swings and her physiology’s changes. The notions are used to describe these symptoms during gestation are “prenatal maternal stress (PMS)”, “maternal anxiety during pregnancy” and “antenatal depression (AD)”. In addition, the lack of extended research and the scientific conflicts arising on the classification problem usually forces scientists to refer to them as “Prenatal maternal stress”. Irrespective of any classification, the stress experienced by the pregnant woman affects her physiology in almost similar manner in every mood alteration (DiPietro, 2004).
Already in the 70s, scientists believed that the emotional state of the mother during pregnancy may affect her fetus. At the present time, recent studies support this hypothesis and indicate that the alterations in pregnant mother’s emotional states are transferred to the unborn child via mother’s emotion based physiological changes. While a natural rise in stress levels may benefit babies helping them to their brain development (Matthews, Owen, Kalabis, Banjamin, Setiawan, Dunn, & Andrews, 2004) and organ mature (Grammatopoulos, 2008). excessive physiological changes may have negative effects on the offspring not only during gestation but in later life of child (Monk, 2001).
Recent research on animals and humans support this notion and indicate that the stress and anxiety of pregnant mother may affect the development of the neurobiological substrate of the future emotion regulation characteristics and temperament (Monk, 2001). More specific, these studies have highlighted the importance of the intrauterine environment for physical and neurological development of the fetus/child, due to the high plasticity of the embryonic brain. So, even subtle biochemical changes in the intrauterine environment significantly affect the structure and function of the fetus brain, increasing vulnerability. Chronic stress, anxiety or antenatal depression may lead to an adverse intrauterine environment which is associated with an increased risk of neurodevelopmental and psychiatric disorders in childhood and adulthood.
Recent studies have shown that the prevalence of antenatal depression is relatively high and it is estimated that the proportion is between 7% and 20.5% in the last months of gestation and 16.8% at postpartum depression of the general population (Limlomwongse & Liabsuetrakul, 2006; Koleva, Stuart, O’Hara, & Bowman-Reif, 2011). Despite the scientific recognition that depression during pregnancy is common and may be of greater clinical impact than postpartum depression, the latter has been extensively studied on the previous years but research on antenatal depression is still limited. Similarly, research focused on the implications that antenatal depression has on fetus development, is only recent (Koleva et al., 2011).
This essay is an effort to cover the most recent research on animals and humans showing associations between fetal and child cognitive and neurobehavioraldevelopment and prenatal stress, anxiety and antenatal depression.
Pathways by Which Pregnant Mother’s Emotional States May Affect her foetus
The ways in which emotional state of the mother can affect the baby obviously related to changes in the intrauterine environment through the placenta. These changes are probably due to : a) changes of maternal behavior (e.g., medication, substance abuse, bulimia), b) reduce blood flow so that the embryo be deprived of nutrients and oxygen and c) the transport of elevated stress neurohormones via placenta. In particular, it is believed that increased catecholamine releases may lead to vasoconstriction which, in turns, increases uteroplacental blood pressure (BP). Thereby, increased blood flow induces and nutrition and oxygen and adversely affects on fetal growth and central nervous system(CNS) development (Monk, 2001).
Although the presence of these hormones is considered necessary for normal fetal maturation and the birth process, when they diverge from normal levels may cause changes even in the fetus’s own stress regulating system (Monk, 2001).
Studies with animals have found compelling evidence of association between PMS and fetal development. Although the mechanism by which PMS induces longlasting changes in infants and child behaviour has not been fully elucidated, it is widely considered that deliberate exposure of pregnant animals to acute stressors (e.g., light, heat, electric shock, unpredictable noise and restraint) produces changes in hypothalamic–pituitary–adrenal axis(HPAA) of the fetuses (Monk, 2001) which mainly regulatesstress processes (Seyle, 1975). These changes include deficits in the ability to cope effectively in stressful situations, in learning behavior and motor development (DiPietro, 2004).
Evidence for in support of the above, can be found in recent studies with pregnant elaborated animals – like sheep, monkeys and rats- that were exposed to various stressors.
Thus, studies with sheep that were exposed to PMS indicated statistically significant HPAA’s vulnerability to excessive levels of synthetic glucocorticoids (GCs) mainly during early pregnancy (Rakers, Frauendorf, Rupprecht, Schiffner, Bischoff, Kiehntopf, & Schwab, 2013). Similarly, a study conducted on monkeys have shown that infants whose mothers had been exposed to mild psychological stressor during middle to late gestation, were more likely to develop dysfunctional social behavior and induced adaptation with peers, mainly because of increased stress-related hormones (cortisol and adrenocorticotrophic hormone) in the intrauterine environment (Schneider, Moore, & Kraemer, 2004). Another study indicated that fetal monkeys whose pregnant mothers had been exposed to loud noises (audiogenic stress) showed delayed motor development and attention deficits in infancy, childhood and adulthood (DiPietro, 2004).
In the same way, a plethora of recent studies in rats indicated that PMS alters hormones in utero resulting on fetus’s brain development. In particular, infant rats whose mothers exposed to stress situations demonstrated changes to dysregulation of glutamatergic system (Fumagalli, Pasini, Frasca, Drago, Racagni, & Riva, 2009) and changes on amygdala which is responsible to regulate anxious behavior through the corticotropin-releasing hormone (CRH) system (Brunton, Donadio, & Russell, 2011). In turn, these brain changes of fetus believed that leads offspring to a higher predisposition metabolic disorders (as obesity) (Paternain et al., 2013), to increased spermatogenesis process in pubertal rats (Pallares et al., 2013), to an impaired cognitive development (Paris, & Frye, 2011), to slowed spatial learning (Salomon, Bejar, Schoreraˆ?Apelbaum, & Weinstock, 2011), to heightened anxiety in adulthood (Brunton et al., 2011) and increased risk for development of infantile spasms (Yum, Chachua, Veliskova, & Velisek, 2012).
Animal studies indicate that mood-based alterations in maternal physiology may influence fetal and post birth development. With this in mind, scientists assumed that if PMS exposure can affect animals, this process probably can occur in humans as well.
Maternal Stress in Humans
While evidences for an association between prenatal stress and fetal brain development and behavioral adaptation had been found in animals in the previous years, research focused on humans only recent.
Some studies found a correlation between prenatal anxiety and stress and reduced levels of attention and slower maturing rate in infancy and childhood (Huizink et al., 2003; Gutteling et al., 2006). Many studies have indicated that prenatal stress arise a range of problems for the fetus including attention deficit hyperactivity disorder (ADHD), emotional problems and reduced cognitive development (Talge, Neal, & Glover, 2007). Changes on fetal brain functions and structure have been also found to be correlated with prenatal stress (Buss, Davis, Muftuler, Head, & Sandman, 2010)
Additionally, numerous previous studies have shown that daily hassles, anxiety during pregnancy (Martini et al., 2013) and acute disasters such as earthquakes and terrorist attacks (Yehuda, et al., 2005) have also demonstrated an increased vulnerability to infant cognitive development. Moreover, research has shown a strong association between schizophrenia and extreme maternal stress in the first trimester of gestation (Malaspina et al., 2008).
High levels of maternal stress during gestation are correlated with a significant risk of preterm birth and lower birth weight. A research on 2,593 pregnant women who were diagnosed with high levels of stress and anxiety, predicted low birth weight and pre-term birth even after control of risk factors such as maternal age, education, race, marital status, alcohol and tobacco, use. Another relative study of about 7,000 pregnant mothers demonstrated that anxiety during gestation significantly increased the risk for hyperactivity in 4 year old child. A later study indicated that prenatal maternal anxiety and depression increases the risk of the infant having reduced heart rate variability (HRV) – temporal variation between heartbeats. Furthermore, maternal depressive symptoms results on infants’ lower endurance and motor tone, less activity and more irritability on neurobehavioral tests (Monk, 2001).
To summarize, the most recent studies on humans and animals suggest that increased levels of stress, anxiety and depression during gestation may have implications on fetal neurobehavioral development and possibly significantly affect the later child’s behavior.
Regarding to human evolutionary history, in an ancient stressful environment it could be useful for our ancestors’ surviving to have children who were more anxious or stressed and perhaps with early increased motor development. But in modern world probably these changes cause problems for the child and their social environment. In addition, defining stress seems to be a major problem because it is a matter of subjective appraisal and it is difficult to distinguish it from other personality and psychological characteristics. However, research in this area is still early, the human studies are yet limited and the underlying mechanisms are just starting to be understood. Up to now no causal link can be drawn yet and further research is needed.
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