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Fetal Development

The Beginning

Let’s start from the very beginning with the egg, or also known as the ovum. About every 28 days, or once a month, a female releases an egg. The egg is a single cell that contains 23 chromosomes. Each month a mature egg is released from one of the woman’s two ovaries. This is called ovulation. Ovulation takes place about two weeks after the first day of the last menstrual period.

This is an unfertalized egg: 

During intercourse, a male will release between 100-400 million sperm. Sperm have a laborious journey, in search for an egg to fertilize. Only the strongest make it to the fallopian tubes, which is a few hundred sperm. If a woman has ovulated and released an egg, the sperm will meet that egg in the fallopian tubes. The fallopian tubes is where conception takes place.

The moment of conception is when a new life is created. The 23 chromosomes from the egg and the 23 chromosomes from the sperm come together to make a brand new, unique human being with 46 chromosomes. At this stage, this new life is called a zygote and is smaller than a grain of salt. At the moment of conception all of your genetic information was determined: skin color, gender, hair color and texture, eye color, height.

You’ll notice the different names at different stages: zygote, embryo, and fetus. These are names that describe the stage of development that the baby is in just like we use newborn, infant, and toddler once the baby is born.

3 weeks after conception (5 week gestational age):

At just 21 days after conception the baby’s heart begins to beat. Baby’s major organ systems are taking shape.The brain, spinal cord, heart, eyes, arm and leg buds can be seen. The mother is often just discovering that she is pregnant. 

4 weeks after conception (6 weeks gestational age):

The foundation for every major organ system is already established and developing. The beating heart can be seen on an ultrasound scan and is beating 100 to 120 beats a minute. An adult’s heart beats 60 to 100 times a minute. The baby is developing on a need to basis. One of the very last organs to develop will be the lungs because baby is developing in fluid and isn’t breathing air yet. The umbilical cord provides the baby with the oxygen that it needs. 

5 weeks after conception (7 weeks gestational age):

         Even though the baby weighs 1/30 of an ounce, baby now has all the internal organs of an adult. All major body systems are intact. The mouth, lips, and tongue are developing. At this point the reproductive organs are beginning to form but nothing that mom and dad can see just yet on an ultrasound. At 43 days, brain wave patterns are recorded.

7 weeks after conception (9 weeks gestational age):

        The name for the stage of development has now changed from embryo to fetus. The baby is now in the developmental stage known as fetus because the baby has all of the major organ systems and is a distinctly, recognizable human being. The word fetus means “little one” in Latin. The limbs and fingers are growing rapidly, and the bones in the arms are beginning to calcify and harden. The baby begins moving around. The baby’s movements are not coordinated just yet. And mom cannot feel baby moving at this point…but soon enough. 

8 weeks after conception (9 weeks gestational age):

At 10 weeks, for the first time in development, the brain can make muscles move on purpose. The baby’s facial features are taking shape. The skin is translucent. The skin is the biggest organ and like all the other organs it takes time for it to develop. So overtime, the skin will become less and less transparent. 

10 weeks after conception (12 weeks gestational age):

This is considered the end of the first trimester. The eyelids fuse shut over the eyes up until 7 months. This happens to protect the developing eyes. At this stage the brain can make muscles move on purpose. The baby can flex its arms and legs and moves around testing its new abilities. The baby sleeps and awakens, gets the hiccups, and can feel pain. The fingers and toes are lengthening and separating and have developed soft nails.

11 weeks after conception (13 weeks gestational age):

The baby’s little hands and feet have perfectly formed footprints and fingerprints. No one else in the world has the same prints. Fingerprints and footprints are determined at conception.

14 weeks after conception (16 weeks gestational age):

        The baby’s facial features are developed: eyes, nose, lips, and eyebrows. The baby’s skin produces a protective covering called vermin. It makes the skin appear waxy and shiny. This vernix protects the delicate skin from the constant exposure to the amniotic fluid.


18 weeks:

        Parents can find out the sex of the baby on an ultrasound. The skeleton is hardening and calcifying and is also visible on ultrasound. Baby is practicing its facial expressions such as frowning, squinting, and sticking out the tongue. The baby can coordinate movement of its arms and legs. At this point the mother will begin to feel the baby moving. She will feel a fluttering, butterfly feeling at first.



20 weeks:

        The pregnancy is now half way over. Baby is 10 inches long from head to heel and weighs about 11 ounces. The baby has unique sleeping and waking patterns and even has a favorite position to sleep in. There is a fine hair called luneugo that covers the baby’s body to keep him/her warm. It will fall off within three weeks of birth. 


Interested in learning more about what happens during pregnancy? Find out by clicking here!

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