Original Article
Evidence of a nesting psychology during human pregnancy

https://doi.org/10.1016/j.evolhumbehav.2013.07.002Get rights and content

Abstract

In altricial mammals, “nesting” refers to a suite of primarily maternal behaviours including nest-site selection, nest building and nest defense, and the many ways that nonhuman animals prepare themselves for parturition are well studied. In contrast, little research has considered pre-parturient preparation behaviours in women from a functional perspective. Reports in the popular press assert that women experience “nesting” urges, in the form of cleaning and organizing behaviours. Anthropological data suggest that having control over the environment is a key feature of childbirth preparation in humans, including decisions about where birth will take place, and who will be welcome in the birthing environment. Here, we describe the results of two studies, a large online study comparing pregnant and non-pregnant women, and a longitudinal study tracking women throughout pregnancy and into the postpartum period and comparing non-pregnant women at similar time intervals, using a nesting questionnaire that we developed. We found that women exhibit nesting behaviours, including space preparation and social selectivity, which peak in the third trimester of pregnancy. As is the case with nonhuman mammals, nesting in women may serve a protective function.

Introduction

Parturition and the early days postpartum are extremely vulnerable and critical periods of time. Not only is parturition itself dangerous for the mother and her emerging fetus, but women and their newborn offspring are also at risk of harm, from both predators and conspecific males (reviewed in Hahn-Holbrook et al., 2011). Since fetuses and newborns are vulnerable to pathogens (reviewed in Hahn-Holbrook et al., 2011), conspecifics also pose a threat as potential carriers of disease. This extreme vulnerability renders the space in which the birth and first hours postpartum will take place of fundamental importance. One adaptation used by some mammalian species in order to safeguard the birth, and the newborn offspring, is nesting.

We define human nesting as measurable change in behaviours and attitudes related to birth preparation that happens during pregnancy. Nests provide safety and protection again conspecific and climatic hazards, and also offer more subtle advantages. A safe environment facilitates mother–infant bonding and the development of attachment. Securely attached human infants have been shown to exhibit a variety of benefits, including an increased ability to manage stress and emotions (reviewed in Schore, 2001), more social play (Main, 1983), and enhanced language development (van Ijzendoorn et al., 1995).

Nesting is observed in many mammalian species. The nesting behaviours of rats (Rosenblatt & Lehrman, 1963), mice (Lisk et al., 1969), sows (Thodberg et al., 1999), and rabbits (Ross et al. 1963) have been well characterized. In nonhuman mammals, nesting refers to a suite of parental (usually maternal) behaviours that serve an adaptive function. In contrast to the rigorous attention paid to the function of nesting in nonhuman animals, the current scientific treatment of nesting in women does not usually consider adaptive function (Rubin, 1976, Cranley, 1981, Malnory, 1996). Popular media often describe nesting as the presumably maladaptive actions of a woman who is out of control (Nesting Instinct, n.d, Nesting, n.d). For example, Skolnik (2003) describes nesting in humans as an “…overwhelming urge to clean and organize your home…(that) strikes in mid- to late pregnancy, turning even the most laid-back housekeeper into a mop-wielding maniac.” She cautions pregnant women to take care when indulging the urge to nest.

We expect that a suite of species-typical, preparatory maternal behaviours will typify nesting in human females. We measured two components associated with nesting psychology in women: space preparation and social selectivity. Both space preparation and social selectivity have been observed in species that nest.

Like other aspects of parental care, nesting behaviours, including space preparation behaviours, vary across species, ranging from literal building a nest to birth site-selection. While women don’t literally build nests, like some mammals they are expected to exhibit careful birth-site selection behaviours (Bowyer et al., 1999, Barten et al., 2001). Based on accounts by pregnant women and descriptions offered by the media, manipulation of the physical environment (including cleaning and organizing) is also expected.

The nonhuman literature suggests that nesting decisions determine not only where the birth occurs, but also who is permitted into the birthing environment. Isolation or partial isolation is observed in several species, including rodents; mice, rats, and hamsters (reviewed in Svare, 1981). Increased social selectivity is also found in some nonhuman primates, including monkeys and apes (Trevathan & McKenna, 2003), and even amongst primates that are typically cooperative breeders (Price, 1990). Complete isolation during parturition is a viable option for many primates as fetal emergence patterns allow the mother to manually aid in the birthing process (Trevathan & McKenna, 2003).

Social selectivity serves a protective function in a number of ways. Isolation or partial isolation helps to reduce infanticide by conspecifics, allows the mother and neonate to identify each other, and decreases the risk of infectious disease (Turner et al., 2010). Decreasing the risk of infectious disease is crucial, since mortality rates are the highest during the first year of life. Newborn infants are especially vulnerable, with infectious disease second only to congenital defects in causing infant death (reviewed in Hahn-Holbrook et al., 2011). However, in the human evolutionary history, a significant survival advantage existed for women who had help during labour (Trevathan & McKenna, 2003). Birth attendants may have facilitated stalled delivery, cleared the infant’s mouth of fluid, and removed the umbilical cord from around the infant’s neck.

Given the costs and benefits associated with selecting who will be included in the birthing environment, it is clear that control over the social environment is an adaptive problem that human females would have faced. Anthropological data and evidence from early human ancestors suggest that women in labour are typically attended by at least two birth attendants (Trevathan & McKenna, 2003). Social selectivity is expected to be part of the human nesting psychology: as birth approaches women should show a preference for proximity to potential birth attendants while distancing themselves from individuals who are less trusted.

Section snippets

Study 1: Groupwise effects of pregnancy

The purpose of this research was twofold. First, we tested for evidence of a nesting psychology in women. Second, we aimed to describe the adaptive birth preparation behaviours (i.e., nesting) exhibited by human females. To this end, we developed a questionnaire in order to characterize human maternal nesting including when it occurs and what behaviours it entails. We describe the development of the Nesting Questionnaire and the results of an online study comparing nesting scores in pregnant

Internal validity and reliability of the 16 item nesting scale

As descriptive statistics and validity analyses showed that non-pregnant women and women in the first trimester of pregnancy reported nesting patterns distinct from women in the second and third trimester of pregnancy, the sample used in order to establish the internal validity and reliability of the 16 item nesting scale included only women in the second and third trimester of pregnancy (n = 120).

Mood and energy levels

We measured the impact of several measures of physiological and psychological stress on reported nesting, space preparation, and social selectivity scores. Mood, anxiety, body wellness, tiredness, and physical discomfort were measured with a 5 point-Likert scale, while lethargy included 3 items embedded in the nesting questionnaire (see Table 2 for the lethargy items).

Consistent with previous research (Lubin et al., 1975, Elek et al., 1997, Lee and Zaffke, 1999), our results show that as

Discussion

In a large web-based study we found that nesting behaviours vary as a function of reproductive status and peak in the third trimester of pregnancy. Reliability and validity analyses suggest that nesting is best understood as a multi-factorial scale including space preparation behaviours and an energy burst, as well as social selectivity behaviours, including a preference for familiar places and people, and novelty aversion.

Aspects of space preparation include a focus on home renovations and

Study 2: Longitudinal study of nesting across pregnancy

We measured reported nesting behaviours in pregnant and non-pregnant women from the first trimester of pregnancy through to the postpartum period. A longitudinal design allowed us to measure within subject changes in nesting behaviours across pregnancy and into the postpartum period, while the inclusion of a non-pregnant control group allowed us to establish whether nesting behaviours vary as a function of reproductive status, and how repeated testing influences reported nesting scores.

Questionnaire reliability

In the 3rd trimester session, the nesting scale showed good internal consistency (Cronbach's alpha = .75).We expected moderate test–retest correlations for non-pregnant participants; although women in the non-pregnant group were not expected to change over time, scores may be sensitive to changes in mood, menstrual cycle, or season. We found that, for women in the non-pregnant group, there was a significant correlation between all time points (see Table 5). Overall, these results suggest that

Discussion

In a longitudinal study tracking pregnant and non-pregnant women we found evidence of change in behaviour peaking in the 3rd trimester of pregnancy that is consistent with the idea that human females have a nesting psychology. Rosenblatt (1990) describes the space preparation behaviours of the rabbit as a gradual development that occurs over the course of pregnancy in response to the hormones associated with pregnancy. We found a similar pattern in human females: pregnant women reported more

General discussion

In an online study investigating reported nesting behaviours as a function of reproductive status, and a longitudinal study tracking pregnant and non-pregnant women throughout pregnancy and into the postpartum period, we found that women exhibit nesting behaviours which peak in the third trimester of pregnancy. Nesting in women includes behaviours and attitudes pertaining to space preparation and social selectivity. Nesting behaviours may serve a protective function at a critical period of

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