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HomeHealth articlesprenatal developmentWhat Are the Stages of Prenatal Development?

Fetus - Developmental Stages and Growth Abnormalities

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After eight weeks of fertilization, when the embryo grows inside the mother's womb, it is called a fetus. This article will share detailed information about it.

Medically reviewed by

Dr. Veerabhadrudu Kuncham

Published At October 14, 2022
Reviewed AtOctober 14, 2022

What Is a Fetus?

Prenatal development is as important as postnatal development for the baby. It not only plays a major role in physical development but also in psychiatric development.

Month by month, women’s bodies go through hormonal changes during menstruation cycle. Until women conceive, the cycle goes on every month. Few eggs are released from the ovary, and this phase is called ovulation. When a single egg is fertilized with sperm, it further grows and moves to the fallopian tube to get attached to the endometrium, which confirms the pregnancy as a fertilized egg gets implanted into the uterus wall. On the other hand, when the egg is not fertilized, the thin lining sheds off. Hence the beginning of another menstruation cycle occurs.

When the embryo is formed, the first few weeks are very important for pregnant women. However, once the embryonic period is over, it is now considered a growing fetus. Thus, the first day of the last menstruation cycle is counted as the start of the pregnancy, and it plays an important role in determining the due date for the baby. Every woman has a genetic combination of XX chromosomes, and every man is born with XY chromosomes. Thus, the genes of women (XX) give a single X to an egg, and men give either X or Y to an egg. If the fertilized egg has the XX combination, it is a girl; if it has the XY combination, it is a boy.

What Are the Fetal Developmental Stages?

There are the following fetal developmental stages seen:

Week 3:

  • From three weeks of implantation into the endometrium, nerve formation begins in the embryo.
  • The body releases the hCG (human chorionic gonadotropin) hormone (pregnancy hormone), which stops the formation of eggs.

Week 4:

  • The embryo develops the structures that are responsible for face and neck formation. At this phase, the embryo develops into a fetus.
  • The heart and circulatory systems have started developing.
  • Pregnant women may feel symptoms like dizziness, nausea, swollen breast, and discomfort.

Week 5:

  • It is also known as the “embryonic period,” where the fetus develops blood cells, kidney cells, and external features.
  • The development of the brain and spinal cord starts during this week, and there is a higher risk of babies born with birth defects if there is any injury, drug abuse, or adverse effect of any medicine taken by the mother.

Week 6 to 7:

  • The fetus grows into a bud that further develops extremities like arms and legs.
  • The brain and nervous system are formed along with the electrical activity.
  • The fetus begins to straighten up slightly.
  • Other features like lip and nose are formed. Ears also start forming with a small indented mark on each side of the head.

Week 8:

  • The head of the fetus is equal to half the size of the body.
  • Arms, legs, ears, and neck are more identifiable now.
  • A small movement of the baby starts in the womb. Although the mother does not feel it yet.
  • The fetus also starts developing breathing pathways from its throat to the lungs.

Week 11 to 14:

  • The fetus has a well-defined face now. Nails start appearing on fingers and toes, and the baby can make a fist.
  • The embryonic tail disappears.
  • The fetus can now kick, stretch, and hiccup; however, the mother still cannot feel the movement.

Week 15 to 20:

  • The fetus develops fine hair.
  • The hearing ability of the fetus is developed.
  • Kidneys are developed now.
  • Ears are now close to their final position.
  • In the later stage of this period, the fetus develops senses like smell, vision, touch, taste, and hearing.

Week 22:

  • Eyelashes and eyebrows appear.
  • Increased muscle development leads to the movements of the baby.
  • Heartbeat is significantly heard with a stethoscope.

Week 23 to 30:

  • The baby’s skin is still translucent, and the body is still lean and grows in size with the passing of each week.
  • Somewhere around the 24th week, the mother can feel fetal movements like rolling, swishing, and kicking.
  • Their bone marrow formation, fat storage, hand, foot, and fingerprint formation occur.
  • In the womb, the baby starts responding to loud noises. Also, it starts recognizing the voice by picking up the sound.
  • The fetus can now inhale and exhale amniotic fluid because the lungs are developed.
  • Later in this stage, the sleep cycle of the baby is right on schedule, which shows active brain functioning.

Week 31 to 40:

  • Rhythmic breathing, an increase in body weight, and complete development of muscles and bones occur.
  • The sutures of the skull have not fused yet, as they continue to grow until their adulthood.
  • At week 37, it is considered to be full term, and by any day, the mother can experience labor signs and symptoms.

Week 41:

  • With the passing of each day after the 40th week, it is considered to be late-term.
  • With the passing of time, only health-related complications and risks are increased for the baby and the mother.
  • Risks associated with post-term pregnancy include the following:
    1. Stillbirth: It is described as a loss of pregnancy or fetus before the delivery.
    2. Macrosomia: It is the terminology used for describing a fetus larger than normal size.
    3. Postmaturity Syndrome: It is a disorder caused by issue with placental blood supply to the fetus.
    4. Meconium in the Lungs of the Fetus: It can cause serious breathing problems after birth.
    5. Decreased Amniotic Fluid: It can cause the umbilical cord to pinch and restrict the flow of oxygen to the fetus.

What Are the Growth Abnormalities Seen in Fetus?

There are the following growth-related abnormalities seen in a fetus:

How to Manage Fetal Growth?

Following are the options for the management of fetal growth:

  • The mother should go for regular checkups.

  • A balanced diet and active lifestyle are important.

  • Regular yoga and exercise, especially suggested for pregnant women, have proved to be of great help during labor.

  • If required, mothers should take supplements for their health not only during pre-pregnancy or pregnancy but also after pregnancy.


Throughout pregnancy, the health of the mother is as important as the health of the fetus. And with extra care and nourishment, a healthy baby weighing around 7 pounds is born. Moreover, due to immature immunity, it is highly essential to take care of fetuses.

Frequently Asked Questions


Is That a Fetus or a Baby?

The fetus is an unborn baby that, from the eighth week after fertilization, grows inside the mother's uterus until birth. The term baby, the kid, is typical and can refer to any child from birth to the age of four years old.


What Is the Age of the Fetus?

During or at the end of the tenth week of the pregnancy, the baby is no longer an embryo. Instead, it is now a fetus, the stage of development until birth. Fetal age is 37 to 39 weeks of pregnancy inside the mother's womb.


How Is a Human Fetus Called?

A newly developing human inside the mother's womb is referred to as an embryo until nine weeks after conception. Then it is then referred to as a fetus. However, in other multicellular organisms, the word embryo can refer more broadly to any early development or life cycle stage before birth or hatching.


What Is it Called Before the Fetus?

Generally, it is called an embryo from conception time until the eighth week of development. After the eighth week, that is called a fetus until it is born. The egg develops into:
 - Blastocyst.
 - Embryo.
 - Fetus.


What Is the Duration of the Fetal Period?

A fetus is a prenatal human being developing between birth and the embryonic stage. The fetal stage starts from the beginning of the ninth week and after fertilization is about 38 weeks, which is the average time of birth. The fetal stage lasts a total of approximately 30 weeks.


At Which Week Does the Fetus Develop?

The fetus develops at the beginning of the 11th or ninth week of pregnancy. It is no longer called an embryo. Instead, a developing baby inside the mother's womb is officially described as a fetus.


Which Is the Last Organ to Develop in a Fetus?

Most babies move to a head-to-down position in the uterus towards the end, with the head placed on the mother's pubic bone. Because the lungs are the last major organ to finish developing, after 24 weeks, the baby will start building up his lungs by breathing amniotic fluid; lungs mostly would not be matured until the 34th week of pregnancy.


In a Developing Fetus, What Is the First Thing to Form?

Four weeks after conception, the neural tube development along the baby's back will be closing. The brain and spinal cord will develop from the neural tube. The heart and other organs also start to form. Structures that are necessary to the formation of eyes and ears.


How Likely Does a Six-Week Fetus Look?

By the time one is six to seven weeks pregnant, there is a prominent bulge where the heart is the bump at the headend in the neural tube. The embryo is curved, has a tail, and looks like a tiny tadpole.


How to Know Whether the Fetus Is Healthy?

A doctor will perform an ultrasound to track the baby's health and developmental growth. Generally, a fetus grows by 2 inches every month. So by the seventh month, the baby should be 14 inches long. By the end of the ninth month, a fetus weighs around 6.61 pounds (Ib) and is 18 to 20 inches long.


How Does the Embryo Grow Inside the Mother's Womb?

During fertilization, the sperm and the egg combine in one of the fallopian tubes to form the zygote. Then the zygote travels down to the fallopian tube to become morula. After reaching the uterus, the morula stage changes to a blastocyst. Finally, the blastocyst burrows into the uterine lining process called implantation.


Inside a Woman, Where Does the Embryo Grow?

The uterus, or womb, is a hollow or pear-shaped organ in a woman's lower stomach area between the bladder and rectum that will be shedding its lining each month during menstruation. A fertilized egg becomes implanted in the uterus, and the fetus starts developing.
Dr. Veerabhadrudu Kuncham
Dr. Veerabhadrudu Kuncham



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