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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
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Home | Pregnancy Timeline | News Alerts |News Archive Aug 25, 2014

A mother rat carrying her tail after delivery. A history of
prenatal stress induced maternal tail chasing activity.

 






WHO Child Growth Charts

 

 

 

Stress in pregnancy passed down for generations

Scientists investigating pregnancies in four generations of rats show that inherited epigenetic effects of stress could affect pregnancies for generations.

To better understand problems during pregnancies today, we should look to the experiences of our ancestors, research published in the open access journal BMC Medicine suggests.

Researchers from the University of Lethbridge in Canada wanted to investigate how preterm births are influenced by stress.


Preterm birth is one of the leading causes of neonatal death and can lead to health problems later in life.


Scientists examined the length of pregnancies in rats because in general there is very little variation between them.

A first generation of rats were subjected to stress late in pregnancy. The following two generations were then split into two groups that were either stressed or not stressed. The daughters of stressed rats had shorter pregnancies than the daughters of those who had not been. Remarkably, the grand-daughters of stressed rats had shorter pregnancies, even if their mothers had not been stressed.

As well as shorter pregnancies, rats whose grandmothers and mothers experienced stress displayed higher glucose levels than the control group. In addition, rats whose grandmothers or mothers who were stressed weighed less.


"We show that stress across generations becomes powerful enough to shorten pregnancy length in rats and induce hallmark features of human preterm birth. A surprising finding was that mild to moderate stress during pregnancy had a compounding effect across generations. Thus, the effects of stress grew larger with each generation."

Gerlinde Alexandra Metz, PhD, Canadian Centre for Behavioural Neuroscience, University of Lethbridge, CA, senior author of the article.


Gerlinde Metz: "Previous epigenetic studies have mainly focused on inheritance of DNA methylation signatures. What we didn't know was whether microRNAs, which are important biomarkers of human disease, can be generated by experiences and inherited across generations. We have now shown that maternal stress can generate miRNA modifications with effects across several generations."


The researchers believe that these changes are due to epigenetics - the arrangement and expression of our genes. In most cases this refers to DNA methylation of the nucleotide base pairs. In this study the researchers believe the epigenetic changes are due to microRNA (miRNA) - non-coding RNA molecules that play a role in regulating gene expression.


Further work needs to be done to understand the mechanisms that generate these epigenetic signatures and how they are passed down from generation to generation. With more knowledge of these mechanisms it may be possible to predict and prevent preterm pregnancy but also other diseases.

Gerlinde Metz: "The findings have implications outside of pregnancy, in that they suggest the causes of many complex diseases could be rooted in the experiences of our ancestors. When we better understand the mechanisms of inherited epigenetic signatures, we can predict disease risk and potentially reduce the future risk of illness."

Abstract
Background
Chronic stress is considered to be one of many causes of human preterm birth (PTB), but no direct evidence has yet been provided. Here we show in rats that stress across generations has downstream effects on endocrine, metabolic and behavioural manifestations of PTB possibly via microRNA (miRNA) regulation.

Methods
Pregnant dams of the parental generation were exposed to stress from gestational days 12 to 18. Their pregnant daughters (F1) and grand-daughters (F2) either were stressed or remained as non-stressed controls. Gestational length, maternal gestational weight gain, blood glucose and plasma corticosterone levels, litter size and offspring weight gain from postnatal days 1 to 30 were recorded in each generation, including F3. Maternal behaviours were analysed for the first hour after completed parturition, and offspring sensorimotor development was recorded on postnatal day (P) 7. F0 through F2 maternal brain frontal cortex, uterus and placenta miRNA and gene expression patterns were used to identify stress-induced epigenetic regulatory pathways of maternal behaviour and pregnancy maintenance.

Results
Progressively up to the F2 generation, stress gradually reduced gestational length, maternal weight gain and behavioural activity, and increased blood glucose levels. Reduced offspring growth and delayed behavioural development in the stress cohort was recognizable as early as P7, with the greatest effect in the F3 offspring of transgenerationally stressed mothers. Furthermore, stress altered miRNA expression patterns in the brain and uterus of F2 mothers, including the miR-200 family, which regulates pathways related to brain plasticity and parturition, respectively. Main miR-200 family target genes in the uterus, Stat5b, Zeb1 and Zeb2, were downregulated by multigenerational stress in the F1 generation. Zeb2 was also reduced in the stressed F2 generation, suggesting a causal mechanism for disturbed pregnancy maintenance. Additionally, stress increased placental miR-181a, a marker of human PTB.

Conclusions
The findings indicate that a family history of stress may program central and peripheral pathways regulating gestational length and maternal and newborn health outcomes in the maternal lineage. This new paradigm may model the origin of many human PTB causes.

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