The First Trimester
Egg Development
Week 1 – period sheds uterine lining, new egg begins to mature and new uterine lining starts to thicken
Week 2 – Egg matures and approaches ovulation (release of the egg to be fertilized)
Zygote Development
Week 3 – Ovulation to 12 – 24 hours – CONCEPTION, single sperm penetrates the egg and a joining of genetic information occurs. A single cell is formed, call a zygote
- Day 2-3 – the zygote travels down the fallopian tube, cells divide into a mulberry-like mass which is 1/100 inch wide, this is called a morula
- Day 5 – with additional cell division, the morula becomes a blastocyst, with an inner core and an outer shell of cells. The outer group of cells become the membranes that nourish and protect the inner group of cells, which becomes the fetus.
- Day 7 – 9 -the blastocyst implants in the uterus. At this point the endometrium (the lining of the uterus) has grown and is ready to support a fetus. The blastocyst burrows into the endometrium where it receives nourishment. It is barely visible, but doubles every 24 hours. The placenta and supporting infrastructure for pregnancy develop at this time as well. It is estimated that up to 5 5% of zygotes never reach this phase of growth
Embryo Development
Week 4 – cells of the embryo are multiplying, and taking on specific functions. This process is called tissue differentiation. Formation of the heart begins, the beginning development of the brain and spinal cord, and the beginning of the gastrointestinal tract.
- MOM – early signs of pregnancy, such as, fatigue, breast soreness, and mood swings
Week 5 – embryo is 1/4 inch long: the beginnings of the vertebra, the lower jaw, the larynx (voice box), and the rudiments of the ear and eye. The heart, which is still outside body, now beats at a regular rhythm. Although arm and leg “buds” are visible with hand and foot “pads,” the embryo still has a tail and cannot be distinguished from pig, rabbit, elephant, or chick embryo.
- MOM – hormone changes will cause swelling of breasts, increase in hunger, and nausea – uterus grows and puts pressure on bladder cause an increase in urination
Week 6 –1/2 inch, 1/1000 of an ounce: the formation of the nose, jaw, palate, lung buds. The fingers and toes form, but may still be webbed. The tail is receding, and the heart is almost fully developed.
- MOM – nausea, morning sickness, food cravings
Week 7 – 7/8 inch, 1/30 ounce (less than an aspirin): the eyes move forward on the face, and the eyelids and tongue begin to form. All essential organs have begun to form.
- MOM – loss or gain of weight
Week 8 -1 inch, 1/15 ounce: The embryo now resembles a human being. The facial features continue to develop and the external genitalia and the external ear appears. The circulation through the umbilical cord is well developed. The long bones begin to form and the muscles are able to contract.
- MOM – uterus grows to the size of an orange – increase in oil secretions and change in hormone may result in skin breakouts – there is about 4 times the normal levels of progesterone and estrogen hormones
Fetus Development
At this point the embryo is developed enough to call a fetus. All organs and structures found in a full-term newborn are present.
Weeks 9 to 12 – Fetus is 3 inches long, 1 ounce: the head comprises nearly half of the fetus’ size and the face is well formed. The eyelids close now and will not reopen until about the 28th week. The tooth buds for the baby teeth appear. The genitalia are now clearly male or female.
- MOM – breasts may be fuller and very sensitive – waistline may be growing – heartburn and indigestion as body adjusts to pregnancy hormones – morning sickness may start to ease – veins in abdomen, breasts, and legs will be more noticeable due to increase in blood volume – uterus grows to the size of a grapefruit – uterus will shift up and forward as it grows and won’t be pressing on bladder – less tired – headaches and light-headedness may occur due the increased blood
The Second Trimester
Weeks 13 to 16 – baby is 6 inches: the skin of the fetus is almost transparent, fine hair develops on the head. The fetus makes active movements, including sucking, which leads to some swallowing of the amniotic fluid. A thin dark substance called meconium is made in the intestinal tract. The heart beats120-150 beats per minute and brain waves detectable.
- MOM – the ligaments that hold up your uterus stretch to accommodate your growing uterus causing some achy-ness – hormones have relaxed bowel muscles causing them to work slower and less efficiently that may result in constipation – uterus is also pressing on your bowel – the veins on your chest and breasts are dilated and more noticeable – the areolas may be darkening and growing in diameter – the uterus is three to four inches below the navel. Fundal height is the distance from the top of the uterus (fundus) to the pubic bone – the uterus is about 1 1/2 to 2 inches below the navel – weight gain is between five and ten pounds
Weeks 17 to 20 – baby is 8 inches: eyebrows and lashes appear and nails appear on fingers and toes. The can mother feel the fetus moving.
- MOM – several skin changes may occur due to hormones such as the “mask of pregnancy” – blotchy patches on your forehead, cheeks, nose and chin, Itchy skin, and/or dry and flaky in certain areas and many pregnant women develop rashes, particularly on the stretched skin – the uterus is at the navel – some tenderness as your belly button becomes an “outtie” from the uterus pressing on it – the line between your navel (linea nigra) and pubic hair has darkened; it will fade after delivery
Weeks 21 to 24 – baby is 11.2 inches, 1 lb. 10 oz.: all the eye components are developed, footprints and fingerprints are forming, and the entire body covered in cream-cheese-like vernix caseosa. The fetus now has a startle reflex.
- MOM – the uterus grows from about 1/2 inch above the navel to 1-1/2 to 2 inches above the navel – the average weight gain is between 10 and 15 pounds at this point – ankles and feet may be swelling – gaining weight more steadily now as your baby continues to fill out – feeling kicks and jabs
The Third Trimester
Weeks 25 to 28 – baby is 15 inches, 2 lbs. 11 oz.: rapid brain development. The nervous system is developed enough to control some body functions, and the eyelids open and close. A baby born at this time may survive, but the chances of complications and death are high.
- MOM – the uterus is the size of a soccer ball, places pressure on your back and pelvis and may cause periodic shooting pains in the lower back and legs, and is close to the rib cage now about 3 inches above the navel – average weight gain is between 17 and 24 pounds at this point
Weeks 29 to 32 – baby is 15 -17 inches, 4 lbs. 6 oz.: there is a rapid increase in the amount of body fat and the fetus begins storing its own iron, calcium, and phosphorus. The bones are fully developed, but still soft and pliable. There are rhythmic breathing movements present, the fetal body temperature is partially self-controlled, and there is increased central nervous system control over body functions.
- MOM – difficulty sleeping – the aorta and vena cava are slightly to the right of the centre of your back, so laying/sleeping on the left side as much as possible ensures an unobstructed blood flow to the organs and extremities – the uterus grows to about 5 inches above the navel and is pushing the organs causing heartburn, constipation, indigestion and breathlessness
Weeks 33 to 36 – baby is 16 -19 inches, 5 lbs. 12 oz. to 6 lbs. 12 oz.: The body hair begins to disappear. A baby born at 36 weeks has a high chance of survival.
- MOM – gaining about a pound a week – mild edema is normal – development of pre -eclampsia. Signs are: severe headache; seeing “spots” or “flashing lights” while at rest; sudden increase in swelling, such as over 2-3 days, especially of the face; abdominal pain; and nausea, vomiting, and feeling sick, contact your caregiver immediately – the cervix may be stretching, thinning (effacement) and opening (dilation) – the average weight gain now is between 25 and 30 pounds
Weeks 37 to 40 – baby is 19 – 21 inches 7 or 8 pounds: At 38 weeks, the fetus is considered full term. It fills the entire uterus, and its head is the same size around as its shoulders. The mother supplies the fetus with the antibodies it needs to protect it against disease.
- MOM – vaginal discharge may be heavier and will have more cervical mucous in it as the body prepares for labor – contractions may be felt – false labor contractions are irregular and can be very painful. These contractions may be felt in various parts of the body (back, lower abdomen, pelvis) – true labor contractions start at the top of the uterus and then spread over the entire uterus, through the lower back and into the pelvis. True labor will become stronger and more painful and won’t be alleviated by changing position – the baby settles into the pelvis – centre of gravity shifts which may make you feel off-balance – easier to breathe – the uterus is pushing on the bladder causing an increase in urination and is 6 1/2 to 8 inches above the navel – labour (labor) may occur anytime
