The nutritional consequences of pregnancy sickness : A critique of a hypothesis

Impact of prenatal stress on offspring glucocorticoid levels: A phylogenetic meta-analysis across 14 vertebrate species

Prenatal exposure to maternal stress is commonly associated with variation in Hypothalamic Pituitary Adrenal (HPA)-axis functioning in offspring. However, the strength or consistency of this response has never been empirically evaluated across vertebrate species. Here we meta-analyzed 114 results from 39 studies across 14 vertebrate species using Bayesian phylogenetic mixed-effects models. We found a positive overall effect of prenatal stress on offspring glucocorticoids (d' = 0.43) though the 95% Highest Posterior Density Interval overlapped with 0 (-0.16-0.95). Meta-regressions of potential moderators highlighted that phylogeny and life history variables predicted relatively little variation in effect size. Experimental studies (d' = 0.64) produced stronger effects than observational ones (d' = -0.01), while prenatal stress affected glucocorticoid recovery following offspring stress exposure more strongly (d' = 0.75) than baseline levels (d' = 0.48) or glucocorticoid peak response (d' = 0.36). These findings are consistent with the argument that HPA-axis sensitivity to prenatal stress is evolutionarily ancient and occurs regardless of a species' overall life history strategy. These effects may therefore be especially important for mediating intra-specific life-history variation. In addition, these findings suggest that animal models of prenatal HPA-axis programming may be appropriate for studying similar effects in humans.

Innate food aversions and culturally transmitted food taboos in pregnant women in rural southwest India: separate systems to protect the fetus?

Pregnancy increases women's nutritional requirements, yet causes aversions to nutritious foods. Most societies further restrict pregnant women's diet with food taboos. Pregnancy food aversions are theorized to protect mothers and fetuses from teratogens and pathogens or increase dietary diversity in response to resource scarcity. Tests of these hypotheses have had mixed results, perhaps because many studies are in Westernized populations with reliable access to food and low exposure to pathogens. If pregnancy food aversions are adaptations, however, then they likely evolved in environments with uncertain access to food and high exposure to pathogens. Pregnancy food taboos, on the other hand, have been theorized to limit resource consumption, mark social identity, or also protect mothers and fetuses from dangerous foods. There have been few tests of evolutionary theories of culturally transmitted food taboos. We investigated these and other theories of psychophysiological food aversions and culturally transmitted food taboos among two non-Western populations of pregnant women in Mysore, India, that vary in food insecurity and exposure to infectious disease. The first was a mixed caste rural farming population (N = 72), and the second was the Jenu Kurubas, a resettled population of former hunter-gatherers (N = 30). Women rated their aversions to photos of 31 foods and completed structured interviews that assessed aversions and socially learned avoidances of foods, pathogen exposure, food insecurity, sources of culturally acquired dietary advice, and basic sociodemographic information. Aversions to spicy foods were associated with early trimester and nausea and vomiting, supporting a protective role against plant teratogens. Variation in exposure to pathogens did not explain variation in meat aversions or avoidances, however, raising some doubts about the importance of pathogen avoidance. Aversions to staple foods were common, but were not associated with resource stress, providing mixed support for the role of dietary diversification. Avoided foods outnumbered aversive foods, were believed to be abortifacients or otherwise harmful to the fetus, influenced diet throughout pregnancy, and were largely distinct from aversive foods. These results suggest that aversions target foods with cues of toxicity early in pregnancy, and taboos target suspected abortifacients throughout pregnancy.

Food Aversions and Cravings during Pregnancy on Yasawa Island, Fiji

Women often experience novel food aversions and cravings during pregnancy. These appetite changes have been hypothesized to work alongside cultural strategies as adaptive responses to the challenges posed by pregnancy (e.g., maternal immune suppression). Here, we report a study that assessed whether data from an indigenous population in Fiji are consistent with the predictions of this hypothesis. We found that aversions focus predominantly on foods expected to exacerbate the challenges of pregnancy. Cravings focus on foods that provide calories and micronutrients while posing few threats to mothers and fetuses. We also found that women who experience aversions to specific foods are more likely to crave foods that meet nutritional needs similar to those provided by the aversive foods. These findings are in line with the predictions of the hypothesis. This adds further weight to the argument that appetite changes may function in parallel with cultural mechanisms to solve pregnancy challenges.

Estimating Effects of Arsenic Exposure During Pregnancy on Perinatal Outcomes in a Bangladeshi Cohort

Supplemental Digital Content is available in the text.

Background:

The relationship between arsenic and birth weight is not well understood. The objective was to evaluate the causal relationship between prenatal arsenic exposure and birth weight considering the potential mediation effects of gestational age and maternal weight gain during pregnancy using structural equation models.

Methods:

A prospectively enrolled cohort of pregnant women was recruited in Bangladesh from 2008 to 2011. Arsenic was measured in personal drinking water at the time of enrollment (gestational age <16 weeks, N = 1,140) and in toenails collected ≤1 month postpartum (N = 624) using inductively coupled plasma mass spectrometry. Structural equation models estimated the direct and indirect effects of arsenic on birth weight with gestational age and maternal weight gain considered as mediating variables.

Results:

Every unit increase in natural log water arsenic was indirectly associated with decreased birth weight (β = −19.17 g, 95% confidence interval [CI]: −24.64, −13.69) after adjusting for other risk factors. This association was mediated entirely through gestational age (β = −17.37 g, 95% CI: −22.77, −11.98) and maternal weight gain during pregnancy (β = −1.80 g, 95% CI: −3.72, 0.13). When exposure was modeled using toenail arsenic concentrations, similar results were observed. Every increase in natural log toenail arsenic was indirectly associated with decreased birth weight (β = −15.72 g, 95% CI: −24.52, −6.91) which was mediated through gestational age (β = −13.59 g, 95% CI: −22.10, −5.07) and maternal weight gain during pregnancy (β = −2.13 g, 95% CI: −5.24, 0.96).

Conclusion:

Arsenic exposure during pregnancy was associated with lower birth weight. The effect of arsenic on birth weight appears to be mediated mainly through decreasing gestational age and to a lesser extent by lower maternal weight gain during pregnancy.

A test of three hypotheses of pica and amylophagy among pregnant women in Tamil Nadu, India

OBJECTIVES

Pica has been studied in India and elsewhere for more than 100 years, yet no compelling and empirically well-supported explanation for it has emerged. Amylophagy, sometimes considered a type of pica and sometimes studied separately, is less frequently investigated and also lacks a convincing explanation. This study used a biocultural approach to test three hypotheses of pica and amylophagy: protection, hunger/nutrition, and psychological distress.

METHODS

The research took place in Tamil Nadu, India. In study 1, a cultural investigation was carried out among nonpregnant, adult women (n = 54) to determine nonfood substances that are consumed in this region and perceptions of health consequences. Next, using the substances identified in Study 1, three hypotheses of pica and amylophagy were tested in a cross-sectional study of pregnant women (Study 2, n = 95). Logistic regression analysis was used to analyze the presence or absence of engaging in pica and amylophagy. A series of bivariate analyses were used to examine the variation in amount and frequency of consumption.

RESULTS

Study 1 revealed that cultural attitudes strongly shape the selection of nonfood substances. In Study 2, the presence or absence of pica was not predicted by any of the variables included in the study, whereas the frequency and amount of consumption of pica substances were primarily explained by the psychological distress and hunger/nutrition hypotheses. Both the presence or absence of amylophagy as well as the frequency and amount of consumption were best explained by the protection hypothesis.

CONCLUSIONS

This research provided partial support for the protection and hunger/nutrition hypotheses for amylophagy, and also provided some evidence for the role of psychological distress and hunger or nutrition in pica.

A biocultural framework for examining maternal cravings and aversions among pastoral women in east Africa

Food preferences during pregnancy result from a complex set of biocultural interactions with important implications for maternal and child health. This article explores the social context of maternal food choice in marginal environments of East Africa. Biocultural data collected among Turkana and Datoga women living in Kenya and Tanzania indicate there is a significant social context to food choice that influences the types of food that women report craving and the food that is consumed. Our framework argues for a deeper understanding of how culture shapes food preferences and how marginalization can constrain access to favored and healthy foods.

Appetite sensations in pregnancy among agropastoral women in rural Tanzania

Women all over the globe report physical and appetite sensations in early pregnancy, and this study contributes to this growing literature by reporting on the appetite sensations experienced by pregnant women from rural Tanzania. Appetite changes associated with 545 pregnancies were compiled from surveys conducted to report on the prevalence of appetite loss, nausea, vomiting, dizziness, joint pain, cravings, aversions, and pica experienced by agropastoral women from rural north-central Tanzania. In addition to these symptoms, specific craved and aversive food groups are described. Statistical associations among appetite sensations, NVP, and birthweight are tested. The only symptom associated with a lower average birth weight for newborns was vomiting. In addition to investigating micronutrient content and chemical properties of specific food and non-food items, future research should include assessing relationships among various appetite sensations and short- and long-term health outcomes for both the mother and child.

Morning sickness: adaptive cause or nonadaptive consequence of embryo viability?

"Morning sickness" is the common term for nausea and vomiting in early human pregnancy (NVP). Recent interest in why NVP occurs-that is, in the evolutionary costs and benefits of NVP-has spurred the development of two alternative hypotheses. The "prophylaxis," or "maternal and embryonic protection," hypothesis suggests that NVP serves a beneficial function by expelling foods that may contain harmful toxins and microorganisms and triggering aversions to such foods throughout pregnancy. The alternative "by-product" hypothesis suggests that NVP is a nonfunctional by-product of conflict--over resource allocation--between the pregnant woman and the embryo. The critical predictions of the prophylaxis hypothesis have been developed and tested, whereas the by-product hypothesis has not been subjected to similar scrutiny. To address this gap, we developed a graphical model and used it to derive predictions from the by-product hypothesis under two different assumptions, namely, that NVP is either (i) a by-product of current conflict between a pregnant woman and an embryo or (ii) a by-product of honest signals of viability produced by the embryo. Neither version of the by-product hypothesis is fully consistent with available data. By contrast, the timing of NVP, its variation among societies, and associated patterns of food cravings and aversions are consistent with the prophylaxis hypothesis.

Is the nausea and vomiting of early pregnancy really feto-protective?

BACKGROUND

Health care providers and popular press articles frequently advise women that nausea and vomiting of early pregnancy (NVP) portends a favorable fetal outcome.

AIM

To investigate the claim that NVP protects against adverse fetal outcomes and improves placental and fetal growth.

METHODS

Data were collected on a prospective cohort of 849 Ecuadorian prenatal patients beginning in early gestation until postpartum. A questionnaire collected information on NVP and other maternal characteristics. Fetal outcomes and placental characteristics were examined using anthropometry and physical examination. Multivariate statistical methods controlled for potential confounders.

RESULTS

Women with nausea only (AOR = 0.45; 95% CI = 0.22-0.94) or nausea with vomiting (AOR = 0.66; 95% CI = 0.46-0.99) had significantly decreased miscarriage risk although the strength of the protection appeared less than that reported for other populations. NVP was not associated with low birth weight, preterm delivery, congenital anomaly, or other outcomes excepting slightly increased mean infant thigh skinfold (P = 0.024), mid-upper arm circumference (P = 0.049), and placental weight (P = 0.034).

CONCLUSIONS

The data did not support the common belief that NVP protects against multiple adverse outcomes. Placental weight was slightly increased in women with NVP but this difference was not reflected in higher birth weights or other types of fetal growth except of marginally increased limb fat.