There are two ways in which people discuss the time period related to milestones in fetal development: gestational and fertilization age.  These terms can be somewhat confusing since they are based upon different starting points. Fertilization age is a framework of time based upon the point of view of the unborn child.  The gestational (or menstrual) age timeline begins two weeks earlier at the last menstrual period, and is figured from the point of view of the mother.  The framework most often used in discussions about the development of the unborn child is gestational age.

Thus, fertilization takes place at two weeks of gestational age and implantation about one week later.  At this point, genetic instructions from the mother and the father combine to form a zygote, barely visible to the human eye.1  This single cell contains more information than fifty sets of the 33-volume set of the Encyclopedia Britannica.

On the very first day, the first four cell divisions take place as the zygote travels down the mother’s Fallopian tubes towards the uterus, all the while being nourished and protected by the mother’s body.

After five to nine days, it implants in the uterus and from this point onward to about eight weeks is known as an embryo.

Around two weeks after fertilization (four weeks gestational age), the first missed menstrual period happens.  The mother’s menstruation is suppressed by chemical signals emitted by the unborn child.  Also at this point, the child’s first completed brain cells appear.

At three weeks, the pre-born child’s heart is in an advanced stage of formation.  His eyes begin to form, and his brain, spinal column, and nervous system are virtually complete.

At just over three weeks (24 days), his heart begins to beat.

At four weeks, his muscles are developing.  His arm and leg buds are visible, and his first neocortical cells appear.  The neocortex is the seat of complex thinking and reasoning, a feature present in no other mammal.  He has grown in size by a factor of 10,000 since fertilization, and is now 6 to 7 millimeters long (about ¼ inch).  Blood flows in the baby’s veins, separate from his mother’s blood.

At five weeks, the baby’s pituitary gland forming, and the mouth, ears, and nose are taking shape.

At six weeks, the baby’s heart energy output is an incredible 20% that of an adult’s.  Her cartilage skeleton is completely formed and ossification (bone formation) begins.  The umbilical cord has developed.  Her brain coordinates voluntary movement of muscles and the involuntary movement of organs.  Reflex responses are present.

At around 43 days, the baby’s brain waves can be recorded.

At 45 days, he begins spontaneous and voluntary body movements, and his milk teeth buds are present.  Shortly after this, at just seven weeks, his lips are sensitive to touch, and his ears resemble his family’s pattern.  The first fully developed neurons (nerve cells) appear on the top of his spinal cord, beginning the construction of the brain stem, which regulates vital functions such as breathing, the heartbeat, and blood pressure.

At eight weeks, the pre-born baby is well-proportioned, about 1½ inches long and 1/30 of an ounce in weight.  All organs are present, complete, and functioning (except the lungs).  Her heart beats sturdily.  Her stomach produces digestive juices, her liver makes blood cells, and her kidneys are functioning.  Her taste buds are forming and her unique fingerprints are being engraved.  Her eyelids and the palms of her hands are sensitive to touch.  Of the 45 total generations of cell replication that will take place by mature adulthood, fully two-thirds (30) have already taken place.  She now consists of about one billion cells, containing more genetic information than every word communicated by every human being who has ever lived since the beginning of the human race.2

At nine weeks, the pre-born child will bend his fingers around an object placed in his palm.  His fingernails are forming and he sucks his thumb.  One week later, all sections of his body are sensitive to touch.  He swallows, squints, frowns, and puckers up his brow.

By eleven weeks, he makes all facial expressions, including smiling.  He is now breathing amniotic fluid steadily and will continue to do so until birth.  His fingernails and toenails are now present.  His taste buds are working; he will drink more amniotic fluid if it is artificially sweetened, and less if it is given a bitter taste.

By the end of the first trimester (twelve weeks, the point at which most abortions are done), vigorous activity shows the baby’s distinct personality.  Their sleep patterns differ; some babies hiccup constantly, others may cry.  The baby can kick, turn over, curl and fan her toes, make a fist, open her mouth and press her lips tightly together, and practice breathing.  After another week, the preborn child’s facial expressions resemble those of her parents.  Her movements are vigorous and graceful.  Her vocal chords and external sex organs are present, and the sex of the baby can be determined.  The baby can now hear very clearly.

At four months, the preborn baby can grasp with her hands, swim, and turn somersaults.  Her mother may first feel her movements at this time.  Her eyelashes are now present and rapid eye movements (REM), indicative of dreaming, can be recorded.  A very bright light shined on the mother’s abdomen will cause the baby to slowly move her arms to cover her eyes.  Very loud music will cause her to cover her ears.

ultrasound four months

Ultrasound at four months.

By five months, the preborn baby has formed his own unique sleeping habits, and a loud sound such as a slammed door may startle him.  His hearing has a wider range of frequency than an adult’s in both the higher and lower ranges.  He may be soothed to sleep by gentle music.

At six months, most babies can live outside the womb with proper care.  Fine hair grows on his head and eyebrows and he now has eyelashes.  He weighs about 22 ounces and is about nine inches tall.  By seven months, his weight increases to over one kilogram (2.2 pounds).  His eyeteeth are present.  His hands can support his entire weight at this time, and he recognizes his mother’s voice.  Of the 45 total generations of cell replication that will take place by mature adulthood, 38 have already taken place.  He now has about 300 billion cells.

With one month to go, his weight is about two kilograms (4.4 pounds).  If born now, he has more than a ninety percent chance of surviving and being entirely healthy.

In the final six weeks of gestation, the baby gains about an ounce of weight per day.  Hormones released by the child trigger labor.  The lightest baby ever born to survive in good health weighed in at a mere 9.2 ounces.  Of the 45 total generations of cell replication that will take place by mature adulthood, 41 have taken place by birth.  The baby now has about two trillion (2,000,000,000,000) cells.  The remaining four generations of cell replication will occupy all of the person’s childhood and young adulthood. This means, that, in developmental terms, we spend more than 90 percent of our lives in utero.

Fetal Development and the Pro-Life Cause

Everyone should be familiar with our own prenatal histories, not just because it is so fascinating, but because we might save an unborn child ourselves one day with this timeline of fetal development. The greatest pro-life tools are not photographs of aborted late‑term pre-born babies, although these are indeed very powerful images. The most powerful persuaders are the full-color, beautiful, clear ultrasounds of pre-born babies peacefully floating in their mother’s wombs, illustrating fetal development.

3D ultrasound of a baby at about 21 weeks

3D ultrasound at about 21 weeks.

The pro-abortionists clearly know this.  When pro-lifers put up posters or billboards depicting living unborn children in a public place, abortion advocates often loudly object and even vandalize the displays.3  Also, in those rare instances when abortion advocates debate pro-lifers, they try their best to censor such images of ultrasounds.  For example, third-trimester abortionist Warren Hern wrote in 1984, “We respond to all requests from schools for educational presentations concerning abortion.  If the sponsors want both sides presented, however, the presentations must be made on different occasions.  We insist that visual aid materials not be presented by either side.”4

Regarding ultrasonography, abortion advocate Sarah Ackley said, “The anti-abortion movement can, with little effort, marshal such images as evidence of fetal personhood.  With no comparably powerful set of imagery at its disposal thus far, the abortion-rights movement will likely remain on the defensive with respect to questions of fetal personhood.”

Preborn children can be the pro-life movement’s most eloquent messengers ― but only if we are their voice.  This means that we should all be very familiar with the amazing process of fetal development.



  1. All information on fetal development is from Taber’s Cyclopedic Medical Dictionary.
  2. The total amount of information communicated since Adam and Eve were created has been contained in about 12 billion hardback and softback volumes averaging 180 pages and 55,000 words apiece; about 500 billion separate copies of newspapers, magazines, periodicals and newsletters of every description, each averaging 45 pages and 25,000 words; and about 100 billion people having spoken an average of 7,500 words per day for an average 45‑year lifespan. This is a total of 12,331,910,000,000,000,000 words of communication transmitted in every form since human life began on Earth (give or take a few trillion).
  3. There have been dozens of incidents of pro-abortion vandalism of pro-life billboards and posters, including those that show healthy preborn children. For documentation on thousands of incidents of extreme pro‑abortion violence, from mass murder to fatal botched abortions, see the Abortion Violence website at Note: this website is currently down.
  4. Warren Hern, M.D. Abortion Practice [New York City:  B. Lippincott Company], 1984, page 323.