Anxiety or Nervousness Disturbs the Progress of Birth Based on Human Behavioral Evolutionary Biology

Abstract

In general, anxiety or nervousness in pregnant women increases the risk of dystocia. Pregnant women are easily susceptible to anxiousness or nervousness. To support a safe and healthy birthing process, childbirth educators, other health-care professionals, and pregnant women require an in-depth understanding about the disruptive effects of anxiety or nervousness on birth progress. Anxiety and nervousness are difficult to quantify and may be influenced by culture. Therefore, reports comparing anxiety or nervousness with dystocia must include various biases. It is difficult to find this issue by medical research. Here, we discuss links between anxiety or nervousness and disturbance in the progress of birth based on the adaptive standpoint of human behavioral evolutionary biology.

INTRODUCTION

In the year 2016, there were approximately 135 million births globally (Central Intelligence Agency, 2017). Dystocia is one of the complications during birth, which refers to difficult birth characterized by abnormally slow birth (Cunningham et al., 2014). One of the indications for cesarean surgery is dystocia. The familial causes of dystocia are uterine dysfunction, such as hypotonic uterus; fetopelvic disproportion, such as narrow birth canal or excessive fetal size; fetal position abnormality, such as breech presentation or transverse lie and fetal rotation abnormality during labor. In general, anxiety, or nervousness in pregnant women increases the risk of dystocia. Reports have shown that nulliparous pregnant women with a moderate-to-high anxiety score experienced dystocia 10.5 times more than other nulliparous pregnant women (Alijahan & Kordi, 2014). Reports have emphasized the negative consequences of such disturbance in pregnant women (Lothian, 2004; Odent, 1987). Adequate research is not present on the influence of anxiety or nervousness on labor. Biochemical research has shown that self-reported anxiety and endogenous plasma epinephrine were significantly correlated. Higher epinephrine levels were significantly associated with lower uterine contractile activity and longer labor duration (Lederman, Lederman, Work, & McCann, 1978). Some reports examined an association between anxiety or depression and emergency cesarean surgery (Andersson, Sundstrom-Poromaa, Wulff, Astrom, & Bixo, 2004; Chung, Lau, Yip, Chiu, & Lee, 2001; Heimstad, Dahloe, Laache, Skogvoll, & Schei, 2006; Johnson & Slade, 2002; Larsson, Sydsjo, & Josefsson, 2004; Laursen, Johansen, & Hedegaard, 2009; Perkin, Bland, Peacock, & Anderson, 1993; Ryding, Wijma, Wijma, & Rydhstrom, 1998; Wu, Viguera, Riley, Cohen, & Ecker, 2002). The results of these reports were inconsistent, with some reports showing association between the fear of childbirth, depression or anxiety and cesarean surgery (Andersson et al., 2004; Chung et al., 2001; Laursen et al., 2009; Ryding et al., 1998) and others reporting no such association (Heimstad et al., 2006; Johnson & Slade, 2002; Larsson et al., 2004; Perkin et al., 1993; Wu et al., 2002). A prospective cohort study conducted in Denmark had the biggest sample size among all such studies (Laursen et al., 2009). This study analyzed 25,297 healthy nulliparous women. Fear of childbirth in early (16 weeks, 6 ± 29 days) and late (31 weeks, 4 ± 21 days) pregnancy was associated with emergency cesarean surgery, with odds ratio 1.23 (1.05–1.47) and 1.32 (1.13–1.55), respectively.

Historically, clinical studies have primarily led to progress in medicine. The evaluation of associations between anxiety or nervousness and dystocia using clinical studies alone may not be effective because such a clinical study would be chiefly based on interviews of pregnant women, which are likely to involve various biases, such as recall bias, selection bias, nonconformist bias or active co-operator bias. In addition, anxiety and nervousness are difficult to quantify and may be influenced by culture, which would prevent extrapolation across geographical borders. Therefore, we believe that this problem should be considered from a different perspective.

Pregnancy and birth pose risks to mothers and babies. The process of childbirth may result in negative outcomes that are neither perfectly predictable nor avoidable when medical procedures are used, and these outcomes may lead to other negative outcomes. Complications arising from pregnancy and birth have resulted in approximately 500,000 maternal deaths, seven million women with serious long-term problems, and 50 million women with negative health outcomes following birth within 1 year (World Health Organization, 2008). This could result in anxiousness or nervousness in pregnant women. Emotional contagion, a phenomenon in which an individual's emotions and behavior directly trigger similar emotions and behavior in others, is an additional factor contributing to anxiousness or nervousness in pregnant women. When obstetricians diagnose an abnormal course of birth, they may experience anxiety or nervousness themselves due to the fear of not being able to prevent negative outcomes. Emotional contagion can explain the nonconscious communication of anxiety or nervousness among medical professionals to pregnant women. To support a safe and healthy birthing process, childbirth educators, other health-care professionals, and pregnant women require an in-depth understanding about the disruptive effects of anxiety or nervousness on birth progress.

In the present article, we discuss links between anxiety or nervousness and disturbance in the progress of birth based on the adaptive standpoint of human behavioral evolutionary biology.

HYPOTHESIS

Anxious or nervousness disturbs the progress of birth based on the adaptive standpoint of human behavioral evolutionary biology.

EVALUATION OF THE HYPOTHESIS

Why does anxiety or nervousness disturb the progress of birth and how is it linked to human behavioral evolutionary biology?

The chimpanzee-human last common ancestor is considered to have given rise to humans 6 million years ago (Harari, 2011). Several human species have existed through history. However, most of them have become extinct. We (Homo sapiens) are the only extant modern humans. Homo sapiens evolved in East Africa 200,000 years ago (Harari, 2011). Homo sapiens as a species have continually reproduced for 200,000 years. Assuming the human reproductive period to have been between 20 and 40 years of age, Homo sapiens have successfully reproduced at least 5,000 to 10,000 times so far. The essential abilities for producing offspring are survival and reproduction in all species including Homo sapiens. The abilities for survival include acquiring energy (food and water) and protection against external stress (cold, heat, dryness, predation, infection, etc.). The abilities for reproduction are pairing, mating, pregnancy, birth, and nursing. Survival abilities take priority over reproductive abilities. All species and individuals are subject to natural selection, which was advocated by Charles Robert Darwin in the 19th century and is one of the basic mechanisms of evolution. Natural selection includes four processes. First, species reproduce to create offspring. Second, some variations occur in each species. Third, variations which influence survival or reproduction occur. Fourth, heritable variations occur. Individuals with heritable, advantageous survival, and reproductive abilities become more common over generations. In contrast, individuals with heritable, disadvantageous survival, and reproductive abilities become less common over generations, leading to extinction. Individuals need to possess and utilize abilities of survival and reproduction in relevant situations for producing offspring.

All species are divided into r-selected or K-selected organisms. The r-selected organisms produce many offspring, have short life spans and are quick to mature. The cost of producing one offspring is small. Typical examples of r-selected organisms are bacteria and insects. The doubling time of Escherichia coli is approximately 20 minutes. On the other hand, K-selected organisms produce few offspring, have long life spans and are slow to mature. The cost of producing one offspring is high. Typical examples of K-selected organisms are mammals, especially elephants and Homo sapiens. The duration of pregnancy in Homo sapiens is approximately 10 months, and it takes 18 years to reach adulthood. Death of mother and/or baby during birth represents a large cost burden in K-selected organisms. The timing of birth in K-selected organisms is crucial for them to successfully produce offspring.

Fear is one of the basic emotions. Homo sapiens experience fear when in danger or when faced with a fearsome situation. Anxiety is also one of the basic emotions. Homo sapiens experience anxiety in the prospect of a dangerous or negative event. Homo sapiens have probably lived among predators, such as ancestors of the lion or hyena in Africa and have risen from the middle of the food chain to the top within 100,000 years (Harari, 2011). Fear or anxiety could represent a crisis of death and survival abilities take priority over reproductive abilities in such a situation. Homo sapiens probably have a particular ability to survive by stopping birth in such a situation. If any species including Homo sapiens gives birth in the presence of predators, this puts both mothers and babies at risk. During labor in mammals including mice, dogs, sows, or dams, environmental disturbance seemed to prolong labor (Newton, Foshee, & Newton, 1966). In experiments with mice, mean labor times were longer in disturbed mice than in control-group mice (Newton et al., 1966).

One of the important hormones for birth is oxytocin, which is a neuropeptide hormone composed of nine amino acids with a disulphide bridge between its two cysteines (Lee, Macbeth, Pagani, & Young, 2009). Oxytocin is produced by the paraventricular nucleus of the hypothalamus and supraoptic nuclei (Lee et al., 2009). Axons of a majority of magnocellular oxytocin neurons terminate in the posterior lobe of the pituitary. The posterior pituitary releases oxytocin (Standring, 2015). Oxytocin is best known for its role in birth, lactation, and social bonding; it causes uterine smooth muscle contraction during birth and regulates milk ejection. Oxytocin receptors within the uterus are regulated during gestation with a peak on the day of birth (Blanks, Shmygol, & Thornton, 2007). Oxytocin receptors are widely distributed throughout the brain including the olfactory bulb and tubercle, neocortex, endopiriform cortex, hippocampal formation, central and lateral amygdala, bed nucleus of the stria terminalis, nucleus accumbens, and the ventromedial hypothalamus (Insel, Gelhard, & Shapiro, 1991; Veinante & Freund-Mercier, 1997). Axons of hypothalamic magnocellular oxytocin neurons reach the central amygdala (Knobloch et al., 2012). In a human study, greater partner support (self-reported) was associated with higher plasma oxytocin in men and women (Grewen, Girdler, Amico, & Light, 2005). Animal and human studies have hypothesized that imbalance in the oxytocin system is the etiology of anxiety disorders (Neumann & Slattery, 2016). In a postmortem study, arginine-vasopressin and oxytocin neurons in the paraventricular nucleus were activated in patients with major depression or bipolar disorder (Purba, Hoogendijk, Hofman, & Swaab, 1996). There are few human studies on levels of peripheral oxytocin in depressed patients. One report showed no significant difference in plasma oxytocin among 12 depressed patients compared with age-matched controls (van Londen et al., 1997). Another report showed that subjects with higher depressive symptom scores had higher plasma and salivary oxytocin levels (Holt-Lunstad, Birmingham, & Light, 2011). A third report showed that depressed women were more likely than controls to display a dysregulated pattern of peripheral oxytocin release (Cyranowski et al., 2008). Recently, data from a pilot study in African American pregnant women showed that depressive symptoms were associated with low oxytocin levels (Garfield et al., 2015). Based on all the above observations, fear or anxiety seems to affect the oxytocin system. However, the level of peripheral oxytocin is not constant because the half-life of oxytocin in plasma is 1 to 6 minutes and oxytocin is secreted into blood in a pulsatile fashion. It would be ideal, but practically impossible, to investigate the influence of oxytocin or oxytocin receptors in pregnant women's brains on fear or anxiety levels.

Other hormones important in the birthing process are catecholamines, which include dopamine, epinephrine, and norepinephrine. Catecholamines are synthesized in the brain, the adrenal medulla, and the sympathetic nerve fibers, and they are known to be involved in the body's stress response to exogenous situations perceived as dangerous. Catecholamines activate an emotional response in the amygdala leading to fear, anxiety, or anger, dilate the pupils, and increase oxygen uptake. The blood supply is shunted from internal organs, including the uterus, to the heart, the adrenal gland, and the skeletal muscle. These are known as fight-or-flight responses. Higher levels of epinephrine were found to be associated with lower uterine contractile activity in the first stage of labor (Lederman et al., 1978). Homo sapiens have probably lived among predators such as ancestors of the lion or the hyena in Africa. Fear or anxiety could have led to higher catecholamines levels, birth disruptions, and escape from predators, which was beneficial for survival and reproduction.

The amygdala comprises two almond-shaped nuclear structures and is located deep within the temporal lobe of the brain. The amygdala has a central role in emotion, emotional behavior, memory, and motivation. Fear or anxiety is one of the basic emotions. Some sensory signals are directly transmitted to the amygdala from the hypothalamus. Other sensory signals detour through the prefrontal cortex, sensory cortex, or hippocampus before reaching the amygdala (Stahl, 2002). Inputs to the amygdala are analyzed to determine the level of panic, and the fear response may be a subsequent output. It is noteworthy that axons of hypothalamic magnocellular oxytocin neurons reach the central amygdala and posterior lobe of the pituitary and that oxytocin receptors are indeed present in the amygdala (Knobloch et al., 2012). If fear or anxiety does disturb progress of birth, they may be directly or indirectly linked to the oxytocin system through the amygdala.

We can summarize the key issues regarding disturbance of birth caused by anxiety or nervousness as follows. The fetus develops and becomes viable outside of the uterus by late pregnancy. Oxytocin receptors within the uterus and amygdala are expressed. Timing of birth is crucial and affects the survival rate of mother and baby in K-selected organisms such as Homo sapiens. The catecholamines, oxytocin system, and amygdala may be involved in birth timing. Birth should occur in perceptibly safe situations, without negative emotions such as anxiety or nervousness. Avoiding birth in situations of anxiety or nervousness in Homo sapiens represents a survival opportunity to avoid possible death and retain opportunities for future reproduction. Considering the fact that Homo sapiens have continually reproduced for 200,000 years, anxiety or nervousness should disturb progress of birth due to the stated reasons.

CONCLUSIONS

We (Homo sapiens) have continually reproduced for 200,000 years, and the timing of birth is crucial for reproductive success. Birth should be avoided in situations of anxiety or nervousness, because anxiety and nervousness disturb the progress of birth based on the adaptive standpoint of human behavioral evolutionary biology. To support a safe and healthy birthing process, childbirth educators, other health-care professionals, and pregnant women require an in-depth understanding about the disruptive effects of anxiety or nervousness on birth progress.

Biographies

KENJI HISHIKAWA is an obstetric and gynecology doctor at Shonan Kamakura General Hospital. His interests focus on the introduction of brain science to obstetrics.

TAKESHI KUSAKA is a head of Shonan Kamakura Birth Clinic. He tries to reduce dystocia by eduction of birth based on the adaptive standpoint of human behavioral evolutionary biology to pregnant women.

TAKANORI FUKUDA is an obstetric and gynecology doctor at Shonan Kamakura General Hospital. His interests focus on gynecological oncology and minimal surgery.

YUTAKA KOHATA is an obstetric and gynecology doctor at Shonan Kamakura General Hospital. His interests focus on women's health care.

HIROMI INOUE is an obstetric and gynecology doctor at Shonan Kamakura General Hospital. His interests focus on natural birth.

DISCLOSURE

The authors have no relevant financial interest or affiliations with any commercial interests related to the subjects discussed within this article.