Fetal Development

If you’re pregnant or concerned you may be pregnant, you may start to wonder what’s exactly going on in there or how a pregnancy develops. Until you were faced with pregnancy, you may never have cared about human development and tuned it out when they taught this in school. 

By this time, you may have figured out how far along you are and want to know exactly what stage of development your embryo, fetus or baby is in. You may also have heard that in the early stages of pregnancy, it’s simply just a bunch of tissue or cells: but there is so much more going on. It’s a complex and fascinating process. 

Did you know?

Fertilization, the union of a female egg and a male sperm, is the first step in a complex series of events that leads to pregnancy. At the moment the sperm meets the ovum (egg), the union results in a fertilized ovum (zygote), and a new life has begun.[i] At this moment, a distinct and unique set of DNA is created which contain all the instructions needed to create a human life. The only thing that’s still needed is the time to develop.

This process can happen within hours after having unprotected sex, long before you miss your period or suspect you might be pregnant.

Many people debate when life begins; however, the science is clear. In fact, a study titled a Biologists’ Consensus on ‘When Life Begins’ reported that 95% of all biologists affirmed the biological view that a human’s life begins at fertilization.[ii]

[i] [Considine, Douglas (ed.). Van Nostrand’s Scientific Encyclopedia. 5th edition. New York: Van Nostrand Reinhold Company, 1976, p. 943]

[ii] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3211703#maincontent

A new life has been created, now what? Within 24 hours after fertilization, the egg that will become your baby rapidly divides into many cells. By the eighth week of pregnancy, the embryo develops into a fetus. There are about 40 weeks to a typical pregnancy. These weeks are divided into three trimesters. We will break down the milestones in each of those trimesters.

The First Trimester (weeks 1-12)

This is generally the first three months of pregnancy. During this trimester, the most amount of growth and change will occur as the fertilized egg will change from just a small grouping of cells into a fetus that starts to exhibit human features. 

Month 1
All of the materials needed to sustain the baby’s life in the womb are being created, such as the amniotic sac and the placenta, which will feed nutrients as the fetus grows. In these first few weeks the mouth, lower jaw and throat are developing. Blood cells are taking shape, and circulation will begin. The tiny "heart" tube will beat 65 times a minute by the end of the fourth week. By the end of this month the baby is smaller than a grain of rice
Month 2
Facial features begin to develop, all systems are developing rapidly, including the neural system (Brain, spinal cord, nerves) the digestive and skeletal systems. By week 8 the embryo is officially called a fetus and is approximately 1 inch long.
Month 3
The arms, hands, fingers, feet and toes are fully formed. At this stage, the fetus is able to open and close its fists and mouth. The reproductive organs are starting to form and by the end of the month all organ systems and features are in place and over the next few months will continue to grow and mature. The fetus is approximately 3-4 inches long.
Month 1
All of the materials needed to sustain the baby’s life in the womb are being created, such as the amniotic sac and the placenta, which will feed nutrients as the fetus grows. In these first few weeks the mouth, lower jaw and throat are developing. Blood cells are taking shape, and circulation will begin. The tiny "heart" tube will beat 65 times a minute by the end of the fourth week. By the end of this month the baby is smaller than a grain of rice.
Month 2
Facial features begin to develop, all systems are developing rapidly, including the neural system (Brain, spinal cord, nerves) the digestive and skeletal systems. By week 8 the embryo is officially called a fetus and is approximately 1 inch long.
Month 3
The arms, hands, fingers, feet and toes are fully formed. At this stage, the fetus is able to open and close its fists and mouth. The reproductive organs are starting to form and by the end of the month all organ systems and features are in place and over the next few months will continue to grow and mature. The fetus is approximately 3-4 inches long.

The Second Trimester (weeks 13-28)

Month 4
The fetus can suck his/her thumb, stretch, yawn and make faces. The nervous system is starting to function. You can now tell if you are having a boy or a girl. By the end of the month the fetus is approximately 6 inches long.
Month 5
The fetus is developing muscles and you may start to feel movement. Hair begins to grow. By the end of the month the fetus is approximately 10 inches long.
Month 6
Finger and toe prints are now visible and the fetus begins to open and close his/her eyes. The fetus can hear and respond to sounds and you may even feel when they have the hiccups. By the end of the month the fetus is approximately 12 inches long.
Month 7
The fetus continues to mature and starts to put on more body fat. Hearing is fully developed and they respond to sound, pain and light. The fetus is now approximately 14 inches long.
Month 4
The fetus can suck his/her thumb, stretch, yawn and make faces. The nervous system is starting to function. You can now tell if you are having a boy or a girl. By the end of the month the fetus is approximately 6 inches long.
Month 5
The fetus is developing muscles and you may start to feel movement. Hair begins to grow. By the end of the month the fetus is approximately 10 inches long.
Month 6
Finger and toe prints are now visible and the fetus begins to open and close his/her eyes. The fetus can hear and respond to sounds and you may even feel when they have the hiccups. By the end of the month the fetus is approximately 12 inches long.
Month 7
The fetus continues to mature and starts to put on more body fat. Hearing is fully developed and they respond to sound, pain and light. The fetus is now approximately 14 inches long.

The Third Trimester (weeks 29-40)

Month 8
The fetus is still putting on more fat. The brain is developing rapidly and they can hear and see. Most of the internal systems are now well developed and they are approximately 16-18 inches long.
Month 9
The lungs are almost fully developed and functional and the fetus continues to development and mature. The fetus is between 17-19 inches long.
Month 10
The baby is ready to go and may change positions now to get ready for birth and may be moving less as the space is reduced. They may come into the world any day now and are approximately 18-20 inches long.
Month 8
The fetus is still putting on more fat. The brain is developing rapidly and they can hear and see. Most of the internal systems are now well developed and they are approximately 16-18 inches long.
Month 9
The lungs are almost fully developed and functional and the fetus continues to development and mature. The fetus is between 17-19 inches long.
Month 10
The baby is ready to go and may change positions now to get ready for birth and may be moving less as the space is reduced. They may come into the world any day now and are approximately 18-20 inches long.

If you think you may be pregnant the very first thing you need to do before you make any decision regarding your pregnancy is to have the pregnancy medically confirmed. This is done though an ultrasound exam. A pregnancy test alone cannot confirm if the pregnancy is developing in the right place or if it is viable (meaning if the pregnancy is alive and will continue as 1 in 4 pregnancies end in miscarriage). You also need to know exactly how far along you are to know what options are available to you. You can contact us today at 508-438-0144 to book a pregnancy confirmation appointment or contact a pregnancy center in your area. 

Resources

[1] [Considine, Douglas (ed.). Van Nostrand’s Scientific Encyclopedia. 5th edition. New York: Van Nostrand Reinhold Company, 1976, p. 943]

[1] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3211703#maincontent

[1] https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth#:~:text=Within%2024%20hours%20after%20fertilization,are%20divided%20into%20three%20trimesters.

[1] https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302#:~:text=Just%20four%20weeks%20after%20conception,the%20eyes%20and%20ears%20developr area. 

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