Welcome to The Visible Embryo
The Visible Embryo Birth Spiral Navigation
Fetal Timeline--- -Maternal Timeline-----News-----Prescription Drugs in Pregnancy---- Pregnancy Calculator----Female Reproductive System

WHO International Clinical Trials Registry Platform

The World Health Organization (WHO) has a Web site to help researchers, doctors and patients obtain information on clinical trials.

Now you can search all such registers to identify clinical trial research around the world!




Pregnancy Timeline

Prescription Drug Effects on Pregnancy

Pregnancy Calculator

Female Reproductive System


Disclaimer: The Visible Embryo web site is provided for your general information only. The information contained on this site should not be treated as a substitute for medical, legal or other professional advice. Neither is The Visible Embryo responsible or liable for the contents of any websites of third parties which are listed on this site.

Content protected under a Creative Commons License.
No dirivative works may be made or used for commercial purposes.


Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development

Developmental biology - Stress Hormones

Maternal stress creates high stress in baby

The human "fight-or-flight" response is inherited across all vertebrate species but may not be as useful to us today...

Vertebrate species, including humans, exposed to stress pre-natally tend to have higher stress hormones after birth, according to a new Dartmouth-led study published in Scientific Reports. While previous research has reported examples of maternal stress affecting offspring stress hormones in different species, this study is the first to empirically demonstrate prenatal stress on offspring stress based on data from all known vertebrate studies.

Through a meta-analysis of 114 results from a total of 39 observational and experimental studies across 14 vertebrate species with birds, snakes, sheep and humans, research captured the impact of maternal stress on offspring.

Researchers analyzed the role of the hypothalamic pituitary adrenal (HPA)-axis, the physiological system that responds to stress and ultimately is responsible for producing stress hormones glucocorticoids. It mobilizes an animal's response to stress. Offspring exposed in the womb and found to have higher levels of glucocorticoids may reflect a desireable adaptation an increased chance for survival under stress.
Remarkably, the effects of prenatal stress hormones on offspring were consistent across species, regardless of brain or body size. There were also no differences considering sex of offspring, age at time of assessment, timing of stress exposure prenatally, or stress severity.

"Animals, including humans, modify their stress hormones in response to environment. Your stress response is set like a thermostat your body can amp up or down stress hormones in response to anticipated environmental conditions."

Zaneta M. Thayer PhD, Assistant Professor, Anthropology, Dartmouth and lead author.

An animal's stress response tends to be activated by external factors, such as when its see a predator, or whether food is or isn't availabile. One of the studies included in the meta-analysis looked at how maternal stress hormones in pregnant snow hares changed in response to the abundance of their natural predators lynxes, over a 10-year cycle. The team found that in years where there were more lynxes, snow hare offspring had more stress hormones and anti-predator behaviors.

Higher stress hormone levels among offspring may help extend survival, but also come at a cost that can affect other systems, such as sexual reproduction. In humans, the mere anticipation of stress or just thinking about prior experiences of discrimination, or trauma, can activate a stress response. Overactive stress hormones can lead to chronic health problems in humans, including anxiety, depression and cardiovascular disease.
"Our stress response is meant to be adaptive to acute stress, such as being chased by predators. However, humans' stress response is often triggered by social evaluation threats and is not serving the adaptive purpose for which it was designed."

Zaneta M. Thayer PhD

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 (-0.160.95). Metaregressions 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.

Authors: Zaneta M. Thayer, Meredith A. Wilson, Andrew W. Kim and Adrian V. Jaeggi

Return to top of page

Apr 18, 2018   Fetal Timeline   Maternal Timeline   News   News Archive

This graph represents the HPA-axis hormone system that mobilizes animal stress responses.
High maternal stress was found to produce high stress levels after birth in each species.
Image credit: Adrian V. Jaeggi

Phospholid by Wikipedia