How Does Your Baby Grow?

Nobody can tell exactly when your baby was conceived. But fertilization usually occurs about two weeks after the beginning of your last menstrual cycle.


Within a few hours after the egg is penetrated by the sperm in the fallopian tube, the egg begins to divide. In the next three to five days, a cluster of up to 50 cells floats down the fallopian tube to the uterus, where it continues to develop. By the tenth day, the ovum is firmly implanted in the uterine wall. Here it burrows little finger-like projections called "villi" into the blood supply of the uterine lining from which it will take its nourishment... and begins the miraculous growth that will make it a real live baby.


Second Week After FertilizationAs the cluster of cells begins to elongate, a water-tight sac forms around it, gradually filling with fluid. This will serve to cushion the growing life from shocks. Next to this, a tiny yolk sac forms, preparing to produce little blood vessels. Now the placenta--the round, flat membrane that will lie inside the uterine wall--begins to develop. Joined to the umbilical cord, it will take over the job of the more primitive villi, bringing food, water and minerals from the maternal blood to the fetus, and carrying fetal waste to the blood.

Third WeekThe cell cluster is now a hollow structure filled with fluid, measuring only about 1/100 of an inch in diameter (the thickness of a heavy pencil dot). But already there are primitive lung buds...a tube that will be your baby's heart...and a thickening that is the beginning of the central nervous system. The cluster begins to curl up now so that it will fit in its compact home as it grows.

Fourth WeekA primitive face is taking form, with large circles where eyes will appear. The mouth, lower jaw, and throat are developing. Little tubules foreshadow internal organs such as the gallbladder, liver, and stomach. Blood corpuscles are taking shape, and the circulation is beginning. The tiny "heart" tube will be beating 65 times a minute by the end of this week. The embryo as it is now called, will be 3/16 of an inch in length by the end of the week. In one month, the single fertilized egg has grown 10,000 times bigger than when it started.

Fifth WeekBy the end of this week, ears begin to develop from two folds of tissue, buds emerge that will become arms and legs, and your baby's eye lenses begin taking form. There is a tiny depression where the nose will be and an equally tiny thickening that will be the tongue. Eight to ten vertebrae of the backbone have been laid down. The brain, spinal cord, and nervous system are well established. Your baby's primitive blood vessels have begun to function.

Sixth WeekBy now the beating heart can be seen with special instruments. It is still outside the baby's body, but its four chambers are beginning to form. The mouth is still closed, but the digestive tract is developing downward from the mouth cavity. By the end of the sixth week, hollows appear where eyes and ears will form; the beginnings of testes or ovaries have appeared; the brain is growing rapidly; and the entire backbone has been laid down. There is even a skeleton, though it is mostly made up of cartilage, not yet real bone. A "tail" extends from the spinal cord; at this stage, the human embryo resembles that of a pig, rabbit, or elephant. It is now 1/4 of an inch in length.


Seventh WeekThe embryo has become a fetus. Its heart is now within its chest cavity. The tail has all but disappeared. Nasal openings are breaking through. Eyes can now be perceived through closed lids. Little buds signal the beginning of fingers and toes and delicate little muscle fibers are starting. The fetus is 1/2 an inch long and weights 1/1000 of an ounce.


Eighth WeekHuman facial features, particularly the jaws, are becoming well defined. Teeth are being formed. Fingers and toes are present, and external ears form elevations on either side of the head. In boys the penis begins to appear. The fetus is no 7/8 of an inch long and weighs 1/30 of an ounce.


Ninth WeekThe baby's face is now completely formed. The clitoris appears in girls. Your baby now resembles a miniature human, slightly more than one inch in length, weighing 1/5 of an ounce.


Tenth Week: Your baby's eyes have moved from the sides of its head, where they were originally, to the front. In males, the scrotum appears. Major blood vessels have almost reached final form. The heart waves are similar to those of an adult. The baby looks top-yeavy, for the head is almost half its entire size.


End of Third Month: Upper and lower eyelids have met and fused and tear glands are starting to appear. Primitive hair follicles are forming and so are the beginnings of vocal cords. Fingernails are already present and your baby can close his fingers to make tiny fists. He can also open his mouth, purse his lips, and squint up his face. He is now three inches long, and weights about one ounce.

Fourth Month : Your baby's heartbeat is now audible to the doctor's stethoscope. Its brain looks like a miniature adult brain. Sweat glands are forming on palms and soles, and the skin is thickening into various layers. Your baby now has eyebrows and eyelashes, has grown to six ounces, and is 8 1/2 inches in length. It is at this time that many babies start to such their thumbs.

Fifth Month: Your baby's muscles are active now, and by the midpoint of pregnancy, 20 weeks, you will probably have felt "quickening"--the baby's movements. There is hair on his head. He is skinny, but fat is beginning to be deposited under his translucent skin. Twelve inches in length, he weighs about one pound.

Sixth Month: Your baby's skin is wrinkled and has developed a cheese-like protective material called "vernix" which will remain right through birth. The eyes are open and will soon be sensitive to light (although color and form won't be perceived until long after birth). Your baby can now hear sounds. And wonder of wonders--with skin ridges fully formed on palms and soles, your baby now has finger- and footprints. Length, 14 inches. Weight, 2 pounds.


Seventh Month : Fine downy hair covers your baby's body. Taste buds have developed. The male's testicles have descended into the scrotum. By the end of this month, your baby is about 16 inches long, and 3 1/2 pounds in weight. Its organ systems are now adequately well developed so that even if born prematurely, it could probably survive. But the next two months will be periods of growth and maturation to ensure a healthy entry into the world.


Eighth Month: Baby is getting plumper and plumper, and the skin is somewhat less wrinkled as fat takes up the slack. He may now weight more than five pounds, and may be some 18 inches in length. His fingernails are long, extending beyond the fingertips.


Ninth Month: The baby's skin is red but smooth. It looks polished. The only downy hair remaining now is on arms and shoulders. On the head, the hair is about one inch long. Deposit of subcutaneous fat continues. By the end of this month, what was begun from you egg cell measuring 1/200 of an inch in diameter, and your husband's sperm cell, only 1/80,000 the size of the egg, will emerge as a bouncy little infant some 20 inches in length, and weighing an average of 7 pounds.