Fetal Development

Describing the age of your unborn child

The age of your baby is called the gestational age. It is measured in two ways. Scientists calculate the gestational age from the estimated day of conception. Doctors that provide prenatal care and deliver babies measure the baby's gestational age from the first day of your last menstrual period, which is usually about two weeks before conception actually occurs. This section discusses the age of the baby since conception.

The information published here was obtained from several websites, including MedlinePlus, a service of the U.S. National Library of Medicine, http://www.nlm.nih.gov/medlineplus/ency/article/002398.htm, accessed August 12, 2010; Mayoclinic.com, "Fetal development: the first trimester, accessed August 12, 2010, http://www.mayoclinic.com/health/prenatal-care/PR00112; MayoClinic.com, "Fetal development: the second trimester, accessed August 12, 2010, http://www.mayoclinic.com/health/fetal-development/PR00113; and DrSpock.com, http://www.drspock.com/article/0,1510,9851,00.html, "Hearing the Fetal Heartbeat," by Marjorie Greenfield, M.D., accessed August 12, 2010.

Photos at 8, 12, 16, and 20 weeks were provided to Priests for Life by Professor Andrzej Skawina (Collegium Medicum Jagiellonian University, Krakow) and Dr. Antoni Marsinek, MD (Czerwiakowski Gynecological and Obstetrics Hospital, Krakow); accessed on August 12, 2010 at http://www.priestsforlife.org/resources/abortionimages/fetaldevelopment.htm .

4 Weeks

Your baby has attached to your uterine wall where she (or he) will spend the next 9 months.
The digestive system, brain and spinal cord have already begun to form.
The heart is beating. Many people are not aware that the baby's heart starts beating 21 days after conception, although it can't yet be heard, even with amplification.

6 Weeks

Your baby's ams and legs are beginning to grow.
Hands and feet can be distinguished and have fingers and toes (may still be webbed).
Eyes and ears are beginning to form.
Lungs start to form.
The upper lip and nose have formed.

8 Weeks

Baby's facial features continue to develop.
All essential organs have started forming.
Your baby can move around now, but the movement is so slight you won’t be able to feel it yet.
With luck, it's possible the baby's heartbeat can be heard as early as 8 weeks after conception. Doctors use a Doppler instrument to amplify the heartbeat by bouncing harmless sound waves off the baby's heart. The heartbeat can be heard because the instrument senses the changes in the sound waves caused by the motion of the beating heart.

12 Weeks

Baby is 2 ½ to 3 inches long.
Eyes, hands, feet, fingers and toes are all developing.
Arms and legs are long and thin.
Eyelids are closed to protect the baby's developing eyes.
Even fingernails and earlobes have formed.
Most of the vital organs are in place although not fully formed.
At 12 weeks after conception, the heart beat is so strong it can be heard consistently by a Doppler instrument, described above.
Tooth buds, the beginning of baby teeth, have appeared.
Baby's gender will be identifiable at this point or shortly thereafter.

16 Weeks

Baby grows a soft covering of downy hair to protect her or his skin.
Reflexes have developed to the point that the baby can kick and suck her or his thumb.
Your baby can make facial expressions, such as frowning or squinting.
Bones continue to develop and get harder.
More muscle tissue develops.
Your baby begins to hear and may soon be able to hear your heart beat.

20 Weeks

Eyes are forming at a rapid rate. Eyelashes appear and eyebrows may be visible.
Baby has a fine covering of hair over the whole body.
The baby can swallow.
You can feel your baby move and kick as she or he is finally big enough for you to feel the movements; the baby weighs about a pound now.
The heartbeat can actually be heard with an ordinary stethoscope

Month 6

Baby’s eyes can open and close.
You may feel hiccups.
Baby’s skin is covered in Vernix, a natural coating that protects the baby’s skin.

Month 7

Baby begins to develop layers of fat around her body that will protect her and keep her warm after she is born.
Taste buds are forming.
The baby’s organs are almost mature, but if she is born this early, she will be considered premature and will require extra care.

Month 8

The baby rapidly grows as she prepares for birth.
Movement is so strong it is visible from the outside.
The brain matures at a rapid pace.
The baby’s organs are mature.

Month 9

The baby settles in the lower abdomen as she prepares for birth.
Her lungs are fully mature and ready to survive outside the womb.
Congratulations, your baby is ready to be born!

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