Stages of Pre-Natal Development
Before Fertilization
- An egg (a living, human cell) is released from a woman's ovary during ovulation. The unfertilized egg is quite active! If it remains unfertilized, it will die within 24 hours.
- Several hundred million sperm (also living, human cells) are released during ejaculation. The sperm are active swimmers.
At Fertilization
- A single sperm succeeds in penetrating the egg. About 20 hours later the nucleus of the sperm fuses with the nucleus of the egg, forming a single cell called a zygote.
- The fertilized human egg has the same basic cellular chemistry as all other living things. Comparing our DNA with that of apes, we find 99% of our genes are identical.
At 2 Weeks' Gestation (from Conception)
- A change in the zygote occurs which ends its capability of splitting into twins: "singularity is achieved".
- Pregnancy (with its hormonal changes) begins when and if the zygote implants in the woman's uterus.
- Because of abnormalities, nature has aborted about 55% of all fertilized eggs by this point. Another 12% or more will spontaneously abort sometime after.
At 4 Weeks' Gestation
- The human embryo has a tail and bears a striking resemblance to embryos of other vertebrates, from fish to mammals.
- It has gill-like arches which will grow to form parts of the head and neck; in fish these eventually develop into gills.
- A primitive heart, which generates its own electrical rhythm, is located outside the body, allowing the growing organism to circulate nutrients and waste products.
- Like the embryos of many mammals, human embryos begin without gender.
- The embryo is about half a centimeter in size.
- If a defect occurs during this stage of development, a miscarriage is likely to result.
- It is usually too early in pregnancy for a surgical abortion, but the French abortion pill RU486 (not available in Canada) is effective at this early stage of pregnancy.
At 8 Weeks' Gestation
- The embryo is now called a fetus.
- It has the primitive beginnings of most of the major body organs. Organ functions have not yet developed.
- The heart is beginning to form the typical four-chambered structure of mammals.
- The fetus moves by reflex.
- No brain waves (regular electrical patterns) yet exist.
- The developing eyes start to move from the sides of the head toward the front, the position for a primate. The tail has disappeared.
- The fetus has begun to look human, with a rudimentary face, limbs, hands and feet (webbing disappears). It is structurally immature and functionally quite limited.
- It weights 1/30 of an oz. (1 g.) and is about 3 cm. long.
- About 70% of abortions have taken place by this point.
At 12 Weeks' Gestation
- The second trimester of pregnancy has begun.
- External genital organs begin to differentiate.
- The fetus weighs about one ounce.
- More kinds of reflex movements appear. The brain is not yet well enough organized to control movements or form even the most basic perceptions. It will not be for some time.
- Most miscarriages and 96% of abortions have taken place by this point.
At 16 Weeks' Gestation
- The body of the fetus grows dramatically. It weighs about 6 ounces.
- Its organs continue to grow and differentiate.
- It has no awareness (including no awareness of pain), because the part of the brain that deals with thought and perception, called the neocortex, has not yet begun to develop the necessary interconnections.
- The fetal health test amniocentesis is performed on a small percentage of pregnant women at this point. Less than 3% of such tests result in abortion.
- The pregnant woman will soon begin to feel the fetus' movements for the first time.
At 20 Weeks' Gestation
- The rate of fetal growth is slower.
- Its internal organs continue to mature. The lungs remain immature.
- The eyelids are completely fused.
- In the fetal brain, the first few synapses, or connections, begin to form among the nerve cells in the neocortex, with the greatest part of the process of interconnection yet to follow.
At 24 Weeks' Gestation
- This is the beginning of the third trimester of pregnancy.
- The interconnection or "wiring up" of the fetal brain has begun. The nerve cells of the neocortex begin to synapse with nerve cells from the thalamus, which is the relay point for the body's sensory input. Bursts of recognizable brain waves start to appear among the random signals.
- The earliest point at which a fetus can possibly survive outside the womb is about 23-24 weeks of gestation (500 grams or approximately 1 lb.). At this stage the chance of survival is low and the risk of impairment and disability quite serious.
- Scientists say that this point of survivability will not change in the foreseeable future, because the fetal lung does not mature sufficiently to permit even mechanically-assisted breathing before week 23-24 of gestation.
At 28 Weeks' Gestation
- The eyes are open. The body begins to fatten.
- The greatest degree of interconnection of the neocortex of the brain begins rather abruptly at about the 28th week. Fetal wakefulness and sleep periods begin to appear. Brain wave EEG patterns are about to change.
- This point has been called the onset of cognitive awareness or brain life.
- The lungs are maturing, which increases the chances of survival in the event of premature delivery.
- A miscarriage at this stage is called a stillbirth.
At 32 Weeks' Gestation
- Brain waves are more organized.
- The fetus continues to grow and gain an increased amount of fat.
- The fetus is well enough developed so that, if born, it has a 90% chance of survival.
At 36 Weeks' Gestation
- The fetus will soon be ready to be born.
Birth (38 Weeks' Gestation)
- Birth is a multi-stage process.
- The fetus leaves the woman's body, comes into the world, breathes for the first time, uses new senses and organs, and exists independent of its mother. When a baby is born its voice is heard, and within hours of being born there is a necessity to communicate.
- Birth marks a critical point for both infant and mother. Birth is the moment of social membership into the family, community, culture, and ultimately, history.