The baby’s heartbeat begins early in the pregnancy. You can download the heartbeat by clicking here

Human Development

The age of an unborn child (gestational age) is measured in two different ways. Embryologists (doctors and scientists who study the early stages of pregnancy) measure the age of an unborn child from the estimated day of conception (the time when you actually become pregnant). On the other hand, practicing doctors measure an unborn child’s age from the first day of your last normal menstrual period, which usually occurs two weeks before conception. The development of the unborn child is described below from the day of conception also called fertilization. Stages of development and time periods are approximate and drawn from several sources.

Scientists and doctors sometimes use other terms to refer to the unborn child as it develops before birth. Therefore, in the early stages of development (up to 8 weeks generally) the unborn child may be referred to as an embryo, and in the later stages, the unborn child may be called a fetus.

For additional information on fetal development and abortion, please review this document published by the Pennsylvania Department of Health. Click Here to View Document

Day 1  Fertilization (24 hours)

Sperm joins with the egg, or ovum, to form one cell smaller than a grain of salt. Twenty-three chromosomes from each parent join to form every detail of human development: sex, hair, eye color, height, skin tone, personality, emotional make-up and other inherited characteristics. Everything is in place so that if development continues normally, a baby will be born in 38 weeks.

Days 2-7

The fertilized egg is rapidly dividing as it travels down the fallopian tube into the uterus where for the last two weeks, the lining has been preparing for it. It becomes a cluster of tiny human cells.

Days 8-13

The fertilized egg begins to implant in the lining of the uterus where it will draw nourishment, which enables the baby to grow.  It takes until about day 14 to fully implant.  The tiny human being has approximately 500 cells.  Some cells split off to become the placenta which will provide nourishment for the unborn child.

Day 14

The unborn child at day 14 is 1/25 of an inch or the size of a period at the end of a sentence. The early beginnings of organ systems are forming as cells are dividing that will later become a brain, spinal cord, heart, kidneys and other organs.

Days 15-21

Placental chemicals and hormones will prevent the mother from menstruating. The unborn child is now about 1/17th of an inch. The heart and circulatory system are developing and will be the first organ system to function.

Days 21-23

The cluster of heart cells about the size of a poppy seed begins to beat.

Days 28-34

The backbone and muscles are forming.  Buds that will become arms and legs are appearing.  Eyes and ears are beginning to develop.  The stomach, liver, gall bladder, pancreas, thyroid gland and lungs are beginning to form though not yet working.

The heart is pumping increasing quantities of blood through the circulatory system.

Days 35-41

The head becomes larger. An umbilical cord appears. Tiny nostrils and ear indentations can be seen. Baby is about 1/3 inches or the size of a pencil eraser.

Days 42-48

Webbed fingers can be seen in the hand. The eyes darken as pigment is produced. The unborn child is now approximately the size of a kidney bean or just over 1/2 inch. The beating heart may be detected on an ultrasound. Early brain waves can be recorded. The body may respond to touch or twitch spontaneously.

The liver is now taking over the production of blood cells. The heart when fully developed can beat at 150 beats per minute.
Photo at 6.5 weeks

Week 7

The uterus can be about the size of a tennis ball. The unborn child now about one inch long may begin making purposeful movements by the end of the week. The jaw forms, including teeth buds in the gums. The eyelids seal to protect the child’s developing light-sensitive eyes.  Some pain receptors appear around the mouth and will spread over the entire body by 20 weeks.

Week 8

Now a little more than an inch long, the unborn child has all major organs and body systems. The brain is making 250,000 new neurons every minute this week. The embryo has distinct human characteristics. Forty muscle sets operate in conjunction with the nervous system and the baby might respond to touching its mouth by bending its head away. Bones begin to form. Fingers, toes, elbows and shoulders can be seen. The tiny tongue has taste buds. The placenta takes over the job of nourishing the baby.

Week 9

The unborn child is now called a fetus. The child can now weigh over 1/4 ounce and be 2 inches long. Fingernails and hair are developing. Genitals have begun to form. The kidneys begin to make urine between 9 and 12 weeks.

Week 10

The baby is nearly 3 inches long crown of head to rump and can weigh 4/5 of an ounce. Fingers and toe nails appear. Baby may make a tight fist if palm is stroked.

Week 11

The unborn child is now almost 3.5 inches long crown to rump. Chest muscles move as in breathing and can be seen on ultrasound. The sucking reflex can occur and thumb-sucking has been photographed. Face, arms and legs are sensitive to touch. The nervous system is making 2.5 million new neurons per minute.

Week 12

The unborn child can now exercise, cover its face, turn its head, bend elbows, curl its toes, form a fist, open and close its mouth, squint and frown. Taste buds continue developing. Heart beats at 157 times per minute. Baby can make bouncing and stepping moves inside the womb. The weight can be 1.5 ounces and length 3.5 inches crown to rump.

Week 13

Eyebrows have begun.  The sex of the baby might be apparent. Eyes and ears can look like a baby’s.

Week 14

It’s easy to tell if it’s a boy or a girl as sexual differentiation can be seen.  Baby is now between 4 and 5 inches long crown to rump and weighs approximately 4 ounces.  Baby can hiccup and facial muscles are better able to do a variety of expressions.

Week 15

Fat will build up under the skin to give nourishment and warmth after birth. Fine hair has begun to grow on the head.

Week 16

The unborn child is about 5.5 inches in length crown to rump and weighs a half pound or more. The mother will probably begin to show now. The ears are functioning and can hear the mother’s voice and heartbeat as well as loud external noises. The umbilical cord transports 300 quarts of fluids per day and completes a round trip of fluids every 30 seconds.  The tiny hands begin to grasp and baby is learning to swallow.

Week 18

The unborn child weighs about 12 ounces an is over 6 inches long crown to rump. The mother may feel small movements. Some babies can open their eyes.

Week 20

The unborn child is about 7.5 to 8 inches long crown to rump and weighs about 1 pound. The mother is feeling stronger movement. Baby can grimace or smile. Pain receptors are found throughout the body. Nerve endings and brain can process sensations of touch. Anesthesia may be recommended for any fetal surgeries. The child can touch its face and other body parts. Females will have a lifetime supply of eggs in their ovaries.

Week 21

Baby can breath in and out the amniotic fluid that surrounds it. Fat is being added to the body causing it to look more like a baby.

The Hand of Hope Photo (21 Weeks)

This famous photo was taken by Michael Clancy in 1999 during a spina bifida corrective surgical procedure performed on a twenty-one week old fetus in utero at Vanderbilt University Medical Center. The baby reached out and grabbed the doctor’s finger.
Copyright © 2001 Michael Clancy

Week 22

Baby can weigh 1.5 pounds and is about 8.25 inches long crown to rump. Sleep and wake cycles will appear. Baby may react to loud and startling noises.

Week 23

The mother may feel more movement because the unborn child may start hiccupping or be moving more inside the womb.

Week 24

Baby can weigh 1.5 to 2 pounds and is about 9 inches long crown to rump. Oil and sweat glands are functioning. All organs are in place. Baby can stick out the tongue and open and shut eyes. Finger nails, eyebrows and lashes are clearly present.

Weeks 25

The unborn child could be born in this month and survive with the proper care. Ears begin sensing vibrations. Baby can suck a thumb.

Week 26

The unborn child is about 10 inches long crown to rump, weighs between 2 and 3 pounds, and can double or triple in weight between now and birth. Eyes can open and close. Baby sleeps 20-30 minutes at a time.

Week 27

Bones are fully developed. Lungs are capable of breathing air. The mother may feel jabs from the baby moving about in the womb.

Week 28-29

The child’s hair and eyelashes are visible. The unborn child now uses the senses of vision, hearing, taste and touch. He can recognize his mother’s voice among other voices. The baby is nearly 3 lbs and 10.5 inches crown to rump.

Weeks 30-31

Many babies have inverted to a head down position in the uterus now. The mother will probably begin to feel powerful kicks under her rib cage and the ball of the baby’s head on the pelvic floor. Now measuring about 11 inches crown to rump, the unborn child weighs about 4 pounds. The baby can see light through the walls of the womb and may blink as a response to it.

Week 32

The white skin coating (vernix) begins to thicken with a layer of fat stored underneath for insulation and nourishment. Antibodies increase, and the unborn child absorbs about a gallon of amniotic fluid per day. The mother’s body completely replaces amniotic fluid every 3 hours.

Week 33

If played near womb, fast music can excite while soft music can calm a baby.

Week 34

The baby’s toenails have reached the tips of his toes. The umbilical cord is about 20 inches long and can be 22 inches at birth. The unborn child may be up to 12.5 inches crown to rump, and can weigh 5.5 pounds.

Week 35

Baby’s hand has a firm grasp. The baby’s head will dip or drop into the pelvis, alleviating the woman’s difficulty in breathing that was due to the high position of it previously. The uterus will begin small contractions called Braxton-Hicks.

Weeks 36-37

The heart is pumping 300 gallons of blood per day. Weight can be 6.5 pounds and length13.5 inches crown to rump. He is fully capable of life outside the womb with minimal intervention. The baby’s downy hair and vernix is absorbed into the amniotic fluid and swallowed by the baby. This will produce the baby’s first bowel movement after birth.

Weeks 38

The child’s average weight is about 6-8 pounds. Now measuring 19-20 inches crown to heel, the baby’s heartbeat can be heard outside the womb. The baby is ready at any moment to come into the world.

Some of the information found on this website was derived from the following sources.


The photos depicting the unborn child on this website are from a compact disc (CD) titled “Windows to the Womb” distributed by the Life Issues Institute. Copies of the CD are available from Life Issues Institute at 813-729-3600.


This booklet is distributed by the Pennsylvania Department of Health. You can receive a free copy by calling 717-783-1379 or 717-783-1380.