Pregnancy... First Trimester

Jorieke VennikSam Carver

Larissa Chambers

First Nine DaysDay 0

• Ovulation• Oocyte• Fertilization

Day 1• Fertilized egg (zygote)• First cleavage

Day 2• Cell division divides into two • Cell division divides into four

Day 3 – 4• Cell division divides into eight • Cell uncompacted morula

Day 5 early blastocyst• Trophectoderm• Blastocoels• Inner cell mass

Day 6 – 7 late stage blastocyst (hatching)• Zona pellucida formed

Day 8 – 9 implantation of the blastocyst• Epiblast• Hypoblast

Fertilization

• Fertilization occurs when the sperm meets the egg and the head of the sperm which contains the genetic information successfully enters the egg.

Egg Cell Division

• After fertilization occurs the egg starts to undergo cleavage. It starts to divide from a one cell to two cells to four cells and so on until it reaches sixteen at which point it becomes a morula. The morula goes on to develop into a blastocyst.

Formation of Twins• During the cell divisions from fertilization to morula stages the

formation of twins will usually occur unless the twins are fraternal. Dizygous (fraternal) twins are due to the mother ovulating two eggs which are both fertilized. Monozygous twins are identical because they form from one egg and one sperm and split while still dividing towards the morula stage. Conjoined twins are monozygous twins that don't split fully and are joined by one or more limbs.

Identicaltwins

Identical twins

Fraternal twins

Conjoined Twins

Implantation

• Implantation is an event that occurs early in pregnancy in which the embryo adheres to the wall of uterus. At this stage of prenatal development, the embryo is a blastocyst. It is by this adhesion that the fetus receives the oxygen and the nutrients from the mother to be able to grow

Colour image of a 6 day old human embryo implanting

GastrulationGASTRULATION IS A PHASE EARLY IN THE DEVELOPMENT OF MOST ANIMAL EMBRYOS, DURING WHICH THE MORPHOLOGY OF THE EMBRYO IS DRAMATICALLY RESTRUCTURED BY CELL MIGRATION. GASTRULATION VARIES IN DIFFERENT PHYLA. GASTRULATION IS FOLLOWED BY ORGANOGENESIS, WHEN INDIVIDUAL ORGANS DEVELOP WITHIN THE NEWLY FORMED GERM LAYERS.

GASTRULATION OF A DIPLOBLAST: THE FORMATION OF GERM LAYERS FROM A (1) BLASTULA TO A (2) GASTRULA. SOME OF THE ECTODERM CELLS (ORANGE) MOVE INWARD FORMING THE ENDODERM (RED).

Second Week Of Embryo Development

• The embryo is now composed of about 150 cells. They are divided in three layers that will each develop in an independent manner.

• The internal layer is called the endoderm (or endoblast). This will become the respiratory and digestive system as well as certain glands including the liver, pancreas, thyroid and thymus.

• The middle layer (the mesoderm) will be busy! It will become bones and cartilage, the circulatory system (heart & blood vessels), the inner skin layer (dermis), muscles, excretory system, loins & genitalia and also the outer covering of the internal organs.

• The outer layer (ectoderm or ectoblast) will provide the brain & nervous system along with the epidermis (skin, hair, nails).

• During this second week, the embryo floats freely in the uterus and survives thanks to the secretions of the uterine lining.

Third Week Of Pregnancy

• At the end of the third week, the embryo is well fixed in the wall of the uterus. Your future baby is no longer a fertilised egg, it has become an embryo.

• The brain and the backbone begin to form.• The external covering changes also and begins to

start the process of creating the placenta and the amniotic cavity (which will surround the placenta).

• The heart is still being formed, but it already beats!

Fourth Week • At the end of the first month, the embryo looks like a

small prehistoric creature (or something out of 'Alien').

• Little buds that will become the arms appear on the 26th day. At the 28th day, buds appear that will become the legs.

• On average, the baby is about 3mm from coccyx to the tip of the head (the size of a large grain of rice). In fact, on the 21st day the embryo is 1.5mm and by the 28th day it will be 5mm.

Large Grain of Rice

Fifth Week

• At the end of this week, the basis for the baby's brain are formed, bone marrow and nervous system are in place.

• Brain cells develop at the rate of 250000 per minute! Eyes, ears and mouth begin to form.

• Tissue begins to develop that will form the backbone and the abdominal muscles.

• The baby's heart begins to beat regularly, but so far, it is at the surface of the body and not yet in the chest cavity.• Size: 5 to 7 mm

Week Six

• The head begins to take shape, tiny cavities show the future location of the eyes and ears.

• The digestive tract is in formation but the mouth cannot be opened yet.

• The tissue connecting the embryo to the uterus turns into an umbilical cord. The backbone begins formation. The cluster of cells that will become the testis or ovaries appear.

• Size: 9 to 14 mm

Seventh Week• The muscles and nerves function. the fetus now has reflexes,

so can move spontaneously. The thorax and abdomen are entirely formed. The lungs begin their slow development.

• The heart is now in the thoracic cavity and beats strongly. The head is becoming more prominent and is leaning towards the body.

• The mouth can be opened and the eyes can be seen behind the closed membrane layer that

will become the eyelids.• Fingers begin to appear. The ears are developing as well as the vestibular system (the inner ear which is used for balance).

Twins at seven weeks

Week Eight• This week, the baby graduates from being an embryo and

becomes a fetus.• Up to now, your baby's framework has been made up of cartilage.

From the 47th day, the first bone cells begin to replace this cartilage. The bones for arms and legs begin to harden and joints begin to form.

• The face and jaw is formed, but teeth and facial muscles are only just starting.

• All of the vital organs are in place: heart, lungs, brain, intestines. However, they are all still immature and will develop further. The genitalia begin to form.

• Starting to look like a real human being now.

Ninth Week Of Pregnancy• During this week, baby will open its mouth for the first

time.• Salivary glands and vocal chord begin to form. The eyes

are completely formed, but the membrane that will be the lids keeps them covered still.

• Hands and feet develop the quickest during this week.• Heart is beating at about 150 beats per minute.• Size: 5.5 cm • Weight: 10 g

Week Ten• Thanks to the brain's considerable development, your baby's

head is very big when compared to the rest of the body.• The external part of the ear begins to form in concert with

the development of the inner ear.• Abdominal muscles form stronger and the loins define their

definitive position. Lungs continue their development.• Your baby is now about 5 cm from tip to butt. and 7.5 cm if you count the expanding legs.

Week Eleven • At the beginning of the 11th week of pregnancy, or the ninth

week after conception, your baby's head still makes up about half of its length. But your baby's body is about to catch up, growing rapidly in the coming weeks.

• Your baby is now officially described as a fetus. This week your baby's eyes are widely separated, the eyelids fused and the ears low set. Red blood cells are beginning to form in your baby's liver. By the end of this week, your baby's external genitalia will start developing into a penis or clitoris and labia majora.

• By now your baby may measure about 2 inches (50 millimetres) long from crown to rump and weigh almost 1/3 ounce (8 grams).

Week TwelveLast Week Of Trimester One

• Muscles respond to the brain. This is only a reflex for now because the brain is not yet sufficiently mature to control things yet.

• This simultaneous development of the brain and muscles allows baby to bend arms, twist wrists and elbows and to clench and open the fists.

• The face becomes animated, allowing for pinching of the eyebrows or pursing of the lips. • The placenta begins to function properly during this week. The umbilical chord begins to take the role of blood circulation.

Teratogen For Trimester One

• An excess of Vitamin A during the first trimester of pregnancy can lead to congenital malformations. These malformations effect the brain, heart, liver, lungs, bones and intestines of the fetus. They can occur during any pregnancy and are the highest cause of infant mortality.

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