Milestones of Early Life
Day 1: Conception: Of the 200,000,000 sperm that try to penetrate the mother’s egg cell, only one succeeds. At that very moment, a new and unique individual is formed. All of the inherited features of this new person are already set – whether it’s a boy or girl, the color of the eyes, the color of the hair, the dimples of the cheeks and the cleft of the chin. He or she is smaller than a grain of sugar, but the instructions are present for all that this person will ever become.
The first cell soon divides in two. Each of these new cells divides again and again as they travel toward the womb in search of a protected place to grow.
Day 6-14: The new individual at first attaches loosely to the wall of the womb, then burrows deeply and attaches securely to it over the next week. Sensitive pregnancy tests can now show positive, but this depends on the level of hormone produced by the new life. By the end of the second week, the mother’s menstrual period is suppressed by this hormone (hCG) which is produced by her child.
Day 17: Blood vessels begin to form. Remarkably, the future sex cells that will give rise to sperm or eggs for a new generation begin to group together – only 17 days after this new life is alive itself.
Day 18-20: The foundations of the brain, spinal cord, and nervous system are laid.
Day 21: The baby’s heart begins to beat, unsurely at first, gaining strength day by day. The heart beats 70 times per minute at first, reaching a maximum of 170-190 at seven weeks, and slowing to 160-180 at 9 weeks. A day later the eyes begin to develop. The earliest stages of the ears are present.
Day 26-27: The lungs begin to form.
Day 28-32: Two tiny arms make their appearance and budding legs follow two days later.  The beginnings of the mouth take shape. [The nose starts to develop. The thyroid gland begins to grow. Blood flows in the baby’s veins but stays separate from the mother’s blood. The tongue begins to form. The face makes its first appearance.
Day 36: The baby’s eyes develop their first color in the retina.
Day 40: The baby makes her first reflex movements. She flexes her neck when touched with a fine bristle around her mouth.
Day 41: His fingers begin to form, followed by his toes a few days later.
Day 42: The baby develops nerve connections that will lead to a sense of smell. Her brain is now divided into 3 parts – one to experience emotion and understand language, one for hearing, and one for seeing. Joints begin to form. Mother misses her second period.
Day 44: Buds of milk teeth appear. Facial muscles develop. Eyelids begin to form, protecting the developing eyes. Elbows take shape. Internal organs are present, but immature. 99% of muscles are present; each with its own nerve supply. Electrical activity is detectable in the baby’s brain.
Day 52: Spontaneous movement begins. The baby develops a whole collection of moves over the next 4 weeks including hiccupping, frowning, squinting, furrowing the brow, pursing the lips, moving her arms and legs, turning her head, touching her face, breathing (without air), stretching, opening and closing her mouth, yawning, and sucking.
8 Weeks: The baby is now well-proportioned, and about the size of Mom’s thumb. Every organ is present. The liver is making blood, the kidneys function, and the heart beats steadily. The baby’s skull, elbows, and knees are forming. Of the 4,500 structures in the adult body, 4,000 are already present. The skeleton of the arms and legs and the spine begins to stiffen as bone cells are added.
9 Weeks: If prodded, the baby’s eyelids and hands close. Genitalia that were forming in the 7th week now become visible, indicating whether the baby is a boy or girl. However, the doctor won’t be able to tell by ultrasound until 12 to 20 weeks. Early muscular movements begin. The thyroid gland turns on.
10 Weeks: Fingerprints begin their 7 week long formation. The baby’s fingernails begin to develop. His eyelids fuse together until month 7, protecting his delicate eyes. The number of connections between nerves and muscles has tripled since last week.
11 Weeks: The baby now “practices” breathing, since she will have to breathe air immediately after birth. The baby urinates. Her stomach muscles can contract. Her vocal chords and taste buds form. She can make complex facial expressions and even smile.
12 Weeks: Fine hair begins to grow on the upper lip and chin and eyebrows. The baby swallows and responds to skin stimulation.
13 Weeks: The face is prettier, and facial expressions may resemble the parents. The baby is active, but mom doesn’t feel anything yet.
15 Weeks: A wild production of nerve cells begins and continues for a month. A second surge will occur at 25 weeks.
4 Months: Nostrils and toenails become visible. She may suck her thumb, turn somersaults and has a firm grip. The ovaries of girls contain beginnings of eggs. She begins to develop sleeping habits.
5 Months: The testes descend in boys. Mom may feel him baby kick, turn or hiccup and may be able to identify a bulge as an elbow or head. Each side of his brain has a billion nerve cells.
6 Months: The baby will be able to hear by next week. The child sleeps and wakes, nestling in her favorite positions to sleep, and stretches upon waking up.
7 Months: His eyelids begin to reopen, preparing to see the outside world. Eyelashes have become well developed.
8 Months: Her skin becomes smooth. The pupils of her eye respond to light. Her fingernails reach to the tip of her finger. She is really feeling cramped now.
9.5 Months: The child triggers labor, and birth occurs, an average of 264-270 days after conception.
Not until the baby has gone through all these events on the inside can we see the new child on the outside.