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Home , Fetus, Prenatal development

STAGES OF

College of William and Mary Students for Life 2013 Germinal Period

From conception to implantation Terms to Know

 Conception: the first stage in development in which a sperm cell meets with an

: the single cell formed at conception from the union of the sperm and the ova

: the fertilized ovum once it has begun to multiply into many cells but before implantation

Fertilization – A Unique Human

 When the sperm meets with the egg, a new human, with a DNA structure unique from that of either is formed

 The zygote may have a different type than the

 This is not a small or arbitrary difference

 If the mother has a negative and the zygote has a positive blood type, the mother’s body will fight against the foreign blood, which may cause a (in order to ensure that this does not happen, the woman must receive regular injections before conception occurs)

 If the zygote were simply another part of the woman’s body, it would necessarily be more similar in structure to her DNA and blood The Rest of the Germinal Period

 In total, the germinal period lasts for 8 days (ending well before a woman knows that she is pregnant); she has most likely not yet missed a period  Once the morula attaches to the uterine wall, it is considered an and the germinal period ends  This would be the “clump of cells” appearance that many clinics may refer to; however, this stage ends long before a woman would begin to seek an abortion

The Embryonic Period

From implantation to approximately eight weeks Terms to Know

 Cephalocaudal: the body develops from the head down  Proximodistal: the body develops from the inside out  Gonadal ridges: where sex organs will eventually develop  Embryo: the stage of human development from implantation until all organs begin to develop (roughly 8 weeks)

Development of the Embryo*

 Development is both cephalocaudal and proximodistal; this means that the central nervous system and the are the first things to begin developing

 3 weeks after conception

 The first heartbeat occurs (despite the heart not being fully formed)

 Three major divisions of the brain begin to differentiate (hindbrain, midbrain, and forebrain)

 5 weeks after conception: bronchial buds (which will become ) are formed

 6 weeks after conception:

 Lower jawbone fuses and upper jawbone begins to form

 The external ear begins to form

 The three main parts of the brain are distinct

 7 weeks after conception:

 Although the sex of the embryo has been decided since conception (when the sperm donated either a second – female – or a – male), it is only now that the distinct physical differentiation begins to take place and gonadal ridges begin to form

 Some people seem to believe that it is only at this point that the embryo has a sex, but this is incorrect! They have had the chromosomal make-up to become either a male or female since conception, it is only now that those physical characteristics take form

 Muscles begin to assume their final shapes and relationships

 The brain develops thousands of nerve cells per minute

 8 weeks after conception:

 The external, middle, and inner ears assume their final form – the embryo can hear its mother’s voice and the sounds of its environment

 By the end of this week, the is able to move around slightly and responds to stimulation around its mouth *These are just the major developments; each week has many more milestones not compiled here

The Fetal Period

From approximately eight weeks to Terms to Know

 Fetus: the stage in human development from approximately 8 weeks until birth

 Retroflexion: bending, curving, or turning backward

 Anteflexion: bending, curving, or turning forward Milestones of the Fetal Period

 The fetal period officially begins when all the basic tissues and organs are in place in a rudimentary form and when the skeleton begins to ossify

 10 weeks after conception: intestines are in place and the fetus has the ability to breathe

 12 weeks after conception:

 Sexual characteristics fully defined

 Sucking and swallowing movement

 20 weeks (5 months) after conception: fetus has almost as many nerve cells as it will ever have

 24 weeks (6 months) after conception: olfactory cells are functional and fetus has the ability to smell (only minutes after birth, an will show preference for the smell of its mother and for the smell of its own )

 28 weeks (7 months) after conception: lungs fully formed

 Over the course of the fetal period, all organs continue to grow and develop Sensory Capacities

Movement Motion Any movement 7 weeks Startle response 8 weeks

 At 15 weeks, the fetus is capable of Generalized movements 8 weeks all of the movements observable in a newborn infant 8 weeks  At 20 weeks (5 months), the fetus’ Isolated arm movements 9 weeks middle ear (controlling its sense of balance) begins to develop – this Head retroflexion 9 weeks means that it can sense changes in its mother’s posture and orient itself Hand-face contact 10 weeks accordingly Breathing 10 weeks

 “Breathing” in a fetus is, for obvious Jaw opening 10 weeks reasons, different than in an infant; Stretching 10 weeks however, it makes movements with its chest and lungs that simulate Head anteflexion 10 weeks breathing and will allow it to breathe Yawn 11 weeks

once outside of the womb Suck and swallow 12 weeks Sensory Capacities (Cont’d)

Sight

 At 26 weeks, if a bright light is held against the mother’s abdomen, the fetus may respond with changes in heart rate and movement

 It has been postulated that a fetus sees light similarly to the way a flashlight looks when covered by a hand

 It is important to note that the slow development of sight in a fetus is not something that differentiates it significantly from a newborn; a newborn can only see approximately one foot in front of it; farther than that, the infant can only distinguish shadows and basic shapes

Sensory Capacities (Cont’d)

Hearing Experimental Evidence

Acquisition Experiments  20-24 weeks (5-6 months) after  were played sounds from their own language conception: the fetus responds to as well as sounds only present in other sounds  The infant was then played two sounds, one of which was present in its native language and one of which was not; they responded more strongly to the novel  24-28 weeks (6-7 months) after sound, indicating that they recognized it was not in the conception: the fetus can recognize language they were used to hearing  In another study, still in the womb were shown changes in sounds (begins to to prefer sounds in their native language differentiate the sounds present in the  Evidence for Hearing in the Womb  Infants were read two stories by their , one language its mother speaks from the that had been read aloud to them while they were in sounds present in other languages) the womb and one they had never heard before  The infants were then conditioned to be able to control  what story would be read to them in a lab experiment The sound level of the outside world to (in one group, if they sucked faster, their mothers would read them the familiar story – slower sucking a fetus is roughly equal to the level at would cause their mothers to read the unfamiliar story which one would hear the outside – and in the other group, they had to suck slower to hear the familiar story and faster for the unfamiliar)

world when sitting in a car with the  The infants showed a clear preference for the familiar windows up story and wanted their mothers to read it to them  This indicates that they were not only able to hear the stories read to them in the womb, but remember them  The mother’s heartbeat and voice are as well able to be heard the best

Sensory Capacities (Cont’d)

Taste Experimental Evidence

 Half of a group of pregnant women  7 weeks after conception: were told to drink carrot juice while taste buds are functional pregnant (the other half acted as a control and drank only water)  Fetuses will increase their  When these women had their babies, swallowing when sweet the newborns were tested for taste tastes are presented into preference between plain cereal and the amniotic fluid and will carrot-flavored cereal  The infants of the women who drank decrease their swallowing carrot juice during their when bitter and sour were significantly more likely to tastes are presented (this prefer the carrot-flavored cereal than the infants of the women who only mimics the reaction of drank water

newborns)  This indicates that food preferences are formed in the womb In Conclusion . . .

The prenatal stage is simply one of many stages in the development of every human being.

Note: How could you expect me to end with anything other than an adorable picture of a baby?