Fetal Development

what is fetal development

Learn about Fetal Development!

Pregnancy – Anatomy and Physiology

FIRST TRIMESTER: months 1, 2, and 3
During the first trimester, some women may not feel any changes at all. They suspect a pregnancy because of a missed menstrual period. However, most women will feel some of the common fetal development symptoms listed below:

  • Fatigue
  • Breast enlargement
  • Increased urination
  • Indigestion and vomiting (associated with “morning sickness” which can happen any time during the day or night)
  • Increased appetite


Pregnancy Changes
If sperm are present around the time of ovulation, fertilization of the released egg (ovum) can occur. The sperm swim towards the ovum in the fallopian tube. Fertilization is the joining of the ovum and sperm to form one cell. Conception occurs with the fertilization of an ovum by sperm. Normally, fertilization takes place within the fallopian tube.

Fertilization is the initial process in the development of a new human being-at its earliest stage. Even at this stage of human development, all the genetic information and instructions necessary for growth are present. A genetically-unique cell contains all the information for what this person will ever be. For example, at conception these characteristics have already been determined: hair and eye color, the sex, intelligence, personality type, body build, future shoe size, as well as any inheritable disease.

As the fertilized egg travels down the fallopian tube towards the uterus, it continues to divide and grow. By appoximately day six of development, it reaches the cavity of the uterus.

The uterine lining (endometrium) is thick and prepared for the fertilized egg to attach and embed itself. This process is called implantation. Afterwards, the placenta develops along with the umbilical cord through which the developing baby receives nutrients and oxygen, and eliminates waste.

Month 1
The head and body, including arms and legs begin to form. By day 23 to 25, the heart is beating.

1 month old baby

Month 2 During this time, all internal organs are formed. Fingers become recognizable along with the eyes. The spine and major joints can move. Brain waves can be detected. By the 8th week, the fetus is approximately one inch long.

3 month old babyMonth 3 Facial structures, such as the eyes, nose, ears, and mouth can clearly be seen. Fingerprints as well as soft nails on the fingers and toes develop. There is more coordination in muscle movements. The lungs continue to mature. By the end of the first trimester, the sex organs develop and the fetus is approximately 4 inches long.


SECOND TRIMESTER-Months 4, 5, and 6


  • Continued breast enlargement and yellow liquid (colostrum) may leak from the nipples
  • Quickening or initial movement (kick) of baby felt by the mother
  • Emotional lability (mood swings)
  • Increased abdominal size due to enlarging uterus.




4th month baby developmentMonth 4 During this month, the body parts are fully formed with a strong heartbeat. The ears are functioning. Also, the fetus is kicking, sleeping, and swallowing. The fetus has grown and is about 6 to 7 inches long.




5 month baby developmentMonth 5 The baby becomes very active; mothers can feel kicking movements. Also, there is a rapid growth with the baby reaching about 12 inches in length. In about four months, your baby will be full term and ready for delivery.





6 month gestation ageMonth 6The baby’s skin is covered with fine hairs and a substance that protects it. By the end of this month, the baby can measure up to 14 inches long.




THIRD TRIMESTER-Months 7, 8, and 9


  • Low back pain
  • Continued movements of baby that can be seen and felt on the belly
  • Mild swelling of ankles and heartburn
  • Abdomen becomes firm to touch
  • Continued fatigue
  • Trouble sleeping
  • Painless contractions (Braxton-Hicks)

7th month gestational ageMonth 7 The baby can open and close the eyes as well as suck his/her thumb and hiccup. There is more activity such as kicking and stretching. All senses are continuing to mature-the baby can hear and respond to sounds.





8th month gestational ageMonth 8 The baby reaches length of up to 18 inches. Sleep and wake cycles occur regularly. The skin begins to thicken as the fat layer increases. The brain is increasing in size also.

Month 9 through delivery The baby will begin to move downward, headfirst, into the mother’s pelvis. By now, the lungs have developed and are preparing to breathe air. By the end of the third trimester, the baby weighs between six and nine pounds. Get ready for labor and delivery!

Before You Decide – An Abortion Education Resource. Sterling VA: Care Net, 2002.

Scott JR, DiSaia PJ, Hammond CB, Spellacy WN. Danforth’s Obstetrics & Gynecology, 8th Edition. Philadelphia: Lippincott Williams & Wilkins, 1999.

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