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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.

WHO International Clinical Trials Registry Platform

The World Health Organization (WHO) has created a new Web site to help researchers, doctors and
patients obtain reliable information on high-quality clinical trials. Now you can go to one website and search all registers to identify clinical trial research underway around the world!




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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 April 16, 2014


Formula-fed infants wake less frequently at night,
as it is harder to digest formula than breast milk.

Breastfed infants who are not nursed during the night,
sleep longer than breastfed infants who are nursed at night.

WHO Child Growth Charts




Breastfeeding and infant sleep

Are babies who wake to breastfeed at night trying to delay the birth of a sibling?

In a new article published in the journal Evolution, Medicine, and Public Health, Professor David Haig argues that infants that wake frequently at night to breastfeed are delaying the resumption of their mom's ovulation and therefore preventing the birth of a sibling with whom they would have to compete for milk.

It has already been documented that smaller gaps between births of siblings contributes to increased mortality of those infants and toddlers. This is especially true when parents' resources are scarce and where infectious disease rates are high. Professor Haig believes that the selective benefits of delaying births are strong enough to have created this significant evolutionary response: nightime crying babies.

"The duration of postpartum amenorrhea [lack of a menstrual cycle]is a major determinant of interbirth internals (IBI) in natural fertility populations — those populations which use no medicines to control births; who, with more frequent and more intense nursing, especially at night, have prolonged infertility.

"Natural selection would have preserved suckling and sleeping behaviours in infants to suppress ovarian function in mothers in order to benefit the current infant by delaying a new birth.

"Maximal night waking can be seen to support the greatest benefit of contraceptive suckling — contraception."

David Haig, Public Health Professor Haig,

Haig also points out two other supporting facts. First, formula-fed infants wake less frequently at night, which is explained by the fact that formula is harder to digest and therefore more sleep inducing than breast milk. Second, breastfed infants not nursed during the night, sleep longer than breastfed infants who do nurse at night.

The scientists' attention was also drawn to infants with Prader-Willi syndrome (PWS) – who are often weak at sucking yet sleep a lot – and infants with Angelman syndrome (AS) – who wake frequently during the night. These syndromes are both caused by the deletion of a cluster of imprinted genes at chromosome 15q13. And, this deletion can be found in either parent.

This composite of traits (called a phenotype) suggests that imprinted genes from father (paternal) or mother (maternal) might have opposite effects on sleep in their infants without deletions in chromosome 15q13. In one small-scale behavioural intervention, parents were instructed not to respond to night waking in their children with AS, with dramatic improvements in those infants' sleep quality.

Professor Haig writes: "In the developed world, many of the health advantages of prolonged interbirth internals [BIs] have diminished as more reliable forms of contraception replace lactational amenorrhea [lack of menstrual cylde due to breast feeding].

"Therefore, the selective forces responsible for interbirth internals have been reduced but many associated behaviours remain part of our biological heritage. Though we might question whether modern sleep practices have had unintended consequences for child health, it would be irresponsible to recommend changes in these practices solely on the basis of mismatched outcomes, without more study for the evidence of harm.

The journal has also published five articles and commentaries that respond to Professor Haig's paper from varying perspectives, along with a reply to the responses by the author.

Disrupted sleep is probably the most common complaint of parents with a new baby. Night waking increases in the second half of the first year of infant life and is more pronounced for breastfed infants. Sleep-related phenotypes of infants with Prader-Willi and Angelman syndromes suggest that imprinted genes of paternal origin promote greater wakefulness whereas imprinted genes of maternal origin favor more consolidated sleep. All these observations are consistent with a hypothesis that waking at night to suckle is an adaptation of infants to extend their mothers’ lactational amenorrhea, thus delaying the birth of a younger sib and enhancing infant survival.

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