Trimester 2 | Trimester 3

Fertilization: the sperm and egg join in the fallopian tube to form a unique human being. Forty-six chromosomes combine, which pre-determine all of a person's physical characteristics. Only thirty hours after conception it is no larger than the head of a pin. Still rapidly dividing, the developing embryo, called a zygote at this stage, floats down from the fallopian tube and towards the uterus where it begins development.

Once in the uterus, the developing embryo, called a blastocyst, searches for a nice place to implant, where it actually burrows beneath the surface of the uterus. At 3.5 weeks the embryo will have formed, The unborn child is only one-sixth of an inch long, but is rapidly developing. The backbone, spinal column, and nervous system are forming. The kidneys, liver, and intestines are taking shape. The heart begins development.The yolk sac, produces blood cells during the early weeks of life.
At 4 weeks, the embryo produces hormones which stop the mother's menstrual cycle.
At 5 weeks the embryo is the size of a raisin, it's tiny heart has begun beating. The neural tube enlarges into three parts, soon to become a very complex brain. The placenta begins functioning. The spine and spinal cord grows faster than the rest of the body at this stage and give the appearance of a tail. This disappears as the child continues to grow.

Facial features are visible, the eyes move forward on the face and eyelids begin to form the eyes have a retina and lens. The palate is nearing completion and the tongue begins to form . T. The major muscle system is developed, and the unborn child practices moving. The child has its own blood type, distinct from the mother's. These blood cells are produced by the liver now instead of the yolk sac.

The unborn child, called a fetus at this stage, is about half an inch long and now resembles a human. Facial features continue to develop and the beginnings of external genitalia form. Circulation through the umbilical cord is well developed. The tiny person is protected by the amnionic sac, filled with fluid. Inside, the child swims and moves gracefully. The arms and legs have lengthened, and fingers can be seen and bones begin to form. The toes will develop in the next few days. Brain waves can be measured.

The heart is almost completely developed and very much resembles that of a newborn baby. An opening the atrium of the heart and the presence of a bypass valve divert much of the blood away from the lungs, as the child's blood is oxygenated through the placenta. The eyelids have completely developed fingers, toes and ears are well developed. Twenty tiny baby teeth are forming in the gums.

Vocal chords are complete, and the child can and does sometimes cry (silently). The brain is fully formed, and the child can feel pain. The fetus can make a fist and may even suck his thumb. The eyelids now cover the eyes, and will remain shut until the seventh month to protect the delicate optical nerve fibers.