Lesson 2.4.2

Lesson 2—Fetal Development, Trimester Events, and Environmental Factor

 

Get Focused

 

This illustration is of a silhouette of fetus, in uterus, full term fetus.

© shahar choen/Shutterstock

The process of prenatal development continues after the embryonic period. In the last lesson, you saw how embryonic development progresses from a single cell to an organism of millions of cells, in less than two months. At the beginning of the ninth week of prenatal development, the embryo name is dropped, and the developing offspring is now called a fetus. As the embryo went through morphogenesis, all organ systems were formed, and now just need to mature or develop further. The placenta and umbilical cord are almost completely formed and will soon take over hormonal control of maintaining the pregnancy.

 

Even though prenatal development is divided into the embryonic and fetal development periods, the full pregnancy is divided into 3 trimesters; each trimester is three-months in duration. The first trimester consists of the embryonic development period and the beginning of fetal development. The first 3 months is where the most critical development is taking place, the embryonic development. As mentioned before, this is when all of the organ systems are laid down. For example, the heart begins beating, blood cells flow through blood vessels, limbs are formed, genitals are now present, and the brain, sense organs and nervous tissue is formed.

 

Trimesters 2 and 3 also have significant developmental events which consist of further system development and maturation. Here are just a few interesting developments that occur by the end of each of the next 6 months:

 

End of month 4

  • Baby is developing reflexes, such as sucking and swallowing, and may begin sucking thumb in utero.
  • Tooth buds are developing.
  • Sweat glands are forming on palms and soles.

End of month 5

  • Hair begins to grow on baby’s head
  • Eyebrows, eyelids and eyelashes appear.

End of month 6

  • Skin is covered with protective coating called vernix
  • Baby is able to hiccup

This illustration shows a fetus head and shoulders, at full term in utero.

© Noel Powell/123RF Limited

End of month 7

  • Taste buds have developed
  • Fat layers are forming.

End of month 8

  • Tremendous brain growth occurs at this time
  • Fingernails can now extend beyond fingertips
  • Most body organs are now developed, except for the lungs

End of month 9

  • The lungs are mature.
  • Baby is now fully developed and can survive outside the mother’s body.

Substances and circumstances can affect prenatal development at anytime. However, it is during the first trimester when the developing offspring is most vulnerable to teratogens, substances that can alter normal development. Examples of some teratogens are cigarette smoke, alcohol, drugs, x-rays and there are a host of others. In addition to harmful agents that may be transferred to the embryo and fetus, there are also substances that are essential for proper growth and development.


Proper nutrition, which includes the right amounts of vitamins and minerals, is fundamental to the healthy development of the embryo and fetus. One of the most important vitamins to have sufficient amounts of is vitamin B9, also known as folate, and commonly called folic acid. Folic acid helps to prevent neural tube defects. It is interesting to note that it is very important to have a high amount of folate in a woman’s diet before conception. One of the activities you will be asked to do in this lesson will help you understand why this is so important.

This illustration shows a pregnant woman with a plate of fruit in front of her.

© Gabor Racz/Shutterstock

One couple from the fertility case study has been able to get pregnant, under your care as their fertility doctor. Although Jane and John did not have to undergo hormone or other reproductive enhancement technologies, you did inform them of how to know when ovulation was taking place to enable them to have sexual intercourse at a time when the egg was most receptive to fertilization. Jane and John have now tested positive for high hCG levels, both in a urine and blood tests. These high hormone levels confirm a positive pregnancy test. As they were with their twins, Jane and John are excited, and very interested to follow the development of their new soon-to-be-baby.

 

In this lesson, to understand fertilization and embryonic development, you will examine the following focusing questions:

  • What are the major events of each trimester?

  • What is the significance of the first trimester?

This lesson will take approximately 40 minutes.

 

Module 4: Lesson 2 Assignment

 

The assessments for this lesson are of two types, those that you can evaluate yourself and those that you will submit to your teacher.

You will complete an assignment on the genetic, hormonal and environmental effects on embryonic and fetal development for assessment. Download a copy of the  Bio30 2.4.2 Assignment to your computer now.

 

This assignment will be a complete and check assignment. Complete the assignment and then check your answers against the key provided. Key Link. You do NOT have to submit this assignment.

 

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#2.4.2 Fetal Development

 ** The Self-Check and Try This questions in this lesson are not marked by the teacher; however answering these questions will help you review important information and build key concepts that may be applied in future lessons. You can respond to these mentally, write out your response, or record your answer in any other way that works for you.