Third trimester

Weeks 27 Thru 32 – Gestational Age (Fetal Age – Weeks 25 Thru 30):

The lungs are not fully mature yet, but some rhythmic breathing movements are occurring. The bones are fully developed, but are still soft and pliable. The fetus is storing its own calcium, iron and phosphorus. The eyelids open after being closed, since the end of the first trimester.
Weeks 33 Thru 36 – Gestational Age (Fetal Age – Weeks 31 Thru 34):

This is about the time that the fetus will descend into the head down position preparing for birth. The fetus is beginning to gain weight more rapidly. The lanugo hair will disappear from the skin, and it is becoming less red and wrinkled

Weeks 37 Thru 40 – Gestational Age (Fetal Age – Weeks 35 Thru 38):
The fingernails have grown long and will need to be cut soon after birth. Small breast buds are present on both sexes. The mother is supplying the fetus with antibodies that will help protect against disease. All organs are developed, with the lungs maturing all the way until the day of delivery.

Second trimester

Weeks 14 Thru 16 – Gestational Age (Fetal Age – Weeks 12 Thru 14):

Intestines have returned to his or her abdomen from the umbilical cord.
Urine begins to form and releases into the amniotic fluid
Bone tissue around the head and within arms and legs develops

Red blood cells are forming in your baby's spleen.
You can now find out the babies sex.

Weeks 17 Thru 20 – Gestational Age (Fetal Age – Weeks 15 Thru 18):
Rapid growth is apparent.
Baby's skeleton is developing bones
Scalp hair also is forming

Eyes have begun to face forward and slowly move

The ears are close to reaching their final position.

Skin begins to produce vernix.

Weeks 21 Thru 23 – Gestational Age (Fetal Age – Weeks 19 Thru 21):

Lanugo now covers the fetus’s entire body.
All the components of the eyes are developed. The liver and pancreas are working hard to develop completely.

Weeks 24 Thru 26 – Gestational Age (Fetal Age – Weeks 22 Thru 24)- Beginning The Third Trimester:
The fetus has developed sleeping and waking cycles.

The fetus has a startle reflex, and the air sacs in the lungs have begun formation.
Brain will develop rapidly
The nervous system has developed enough to control some functions.

First trimester

1-3 months

Week 1 & 2 – Gestational Age

Menustrutual cycle has ended and ovulation has begun.

During intercourse Sperm will travel through the cervix and into the fallopian tube.

If conception takes place, the sperm penetrates an egg and creates a single set of 46 chromosomes called a zygote

Divided cells form a morula caused by a fertilized egg that has traveled through the fallopian tube

The morula becomes a blastocyst . the blastocyst will imbed into the uterine lining and begin the embryonic stage.

Week 3 – Gestational Age (Fetal Development – Week 1)

the brain, spinal cord, heart, and gastrointestinal tract develop.

Week 4 & 5 – Gestational Age (Fetal Development – Weeks 2 & 3)

More growth takes place. Arm and leg buds start to become noticeable. The heart developes a steady rhythm. Hormones are being produced due to the placenta.

Week 6 – Gestational Age (Fetal Development – Week 4)
lungs, jaw, nose, and palate begin to form.
Webbed structure on the hand and feet buds will become your toes and fingers.

Brain continues to form
  Week 7 – Gestational Age (Fetal Development – Week 5)
every essential organ has begun to form in the embryo.

The hair and nipple follicles are forming, and the eyelids and tongue have begun formation.
The elbows and toes are more visible as the trunk begins to straighten out.

Week 8 – Gestational Age (Fetal Development – Week 6)

Ears continue to form externally and internally
The embryo now has the same features as an adult human.

Formation of bones start, muscles can contract at this time.

Facial features continue to mature.

Weeks 9 thru 13 – Gestational Age (Fetal Development – Weeks 7 thru 11)
Fetal period begins.

Genitalia form in male or female, but are not noticeable on an ultrasound

The eyelids close and will not reopen until the 28th week of pregnancy.