Fetal development


Fetal development is the most vulnerable phase of an individual due to infections and many other  complication affecting the growth and development of fetus. Nevertheless, it is one of the significant phases in the life of a human being. Fetus is the growing miniature within the mother’s womb and the fetal development is  followed by embryonic development. An embryo or the fetus is greatly exposed to many genetic, social and environmental threats resulting in poor development . Embryonic period extends from day 1 to 6 weeks followed by the fetal period that extends till the birth of the baby. The major areas of concern during the fetal development is the proper assessment, education, support and nutritional care of the pregnant mother. The family should understand the basics of identifying the normalcy of fetus. Therefore, it is important to understand the major milestones of embryonic and fetal development.Let us explore the changes that occur in the embryonic phase.


Embryonic Period

During embryonic development, a number of cellular changes happen as a result of rapid cell multiplication and differentiation. By 6 days after the fertilization, implantation begins. At this time the embryo is made up of simply the ball of cells resembling a bunch of grapes. The cellular mass has a cavity at its centre called the blastocyst. By the end of 2 weeks, implantation is complete while the placental circulation starts. At 2 weeks, embryo is distinguished by 2 distinct layers, endoderm- the inner layer of cells and ectoderm- the outer layer of cells simultaneously, the amnion has also begun to form at this phase. By the third week, the third germ layer mesoderm is ready to appear. Through an ultrasound scanning, we can visualize the primitive neural tube, blood vessels, and the paired heart tubes that starts pumping the blood. Between 4th to 8th week, an embryologic plate along with the cranial and caudal ends of the nervous system appear. By end of 2nd week, the budding of arms and legs helps the mass look-like a miniature human-like shape. Some basic forms of skeletal muscle and vertebrae also start appearing at this phase. By the beginning of the third month, the minute baby measure about 3 cm.



Fetal Period

Fetal period starts from the beginning of the week 9 and extends till the birth of the baby.  Major physical changes during this phase consist of rapid body growth and differentiation of various bodily tissues, organs, and organ systems. By the time fetus enters the 10th week, the face is visible however, it is not very clear. By the end of the third month, the stomach, small intestine, and large intestine begins to form. At this stage, they look like open tubular structures instead of well-defined organs.  By the time of 12 weeks, the gender of the baby can be determined because of external genitals. The developemnt of lungs  continue with the budding of bronchi, bronchioles, and small alveolar divisions. By week 20-24, primitive alveoli are completely formed. During the third trimester (7th to 9th month of pregnancy) weight triples and length doubles.


Fetal development by month



It is the period of early embryonic growth ranging from the day of fertilization to 2 weeks. It includes implantation and the formation of primary chorionic villi. During this period, embryo develops into two cell layers called trophoblast and blastocyst along with the amniotic cavity .



An embryo, a the end of 6 weeks of growth, measures  approximately  1.2 centimeters long. During this time arm and leg buds are visible and the rudiments of the eyes, ears, and nose tarts to showup . Additionally, lung buds , primitive intestinal tract and the cardiovascular system starts workingNeural tube   forms the brain and spinal cord and it gets closed by the 4th week.



It ranges from 7 to 10 weeks , and the 9 weeks marks the transition between embryonic period and the fetal period. Fetus at this stage measures approximately 6.3 cm from crown to rump and weighs hardly 28g . By the middle of this phase most of the major organs are formed . External genitalia begin to appear and the heart forms 4  chambers by  week 7. Fetus look-like a miniature human with the bones being ossified and the rudimentary kidney begins to secrete urine.



It marks the weeks 11-14, by the end of 14 weeks  the fetus is approximately 12 cm crown-rump length and  weighs about 110 g. By this time, fetal head is slightly erect and the  lower extremities are well developed. Hard palate and nasal septum have fused. Male and female can differentiated at this phase as the external genitalia is clear . The eyelids are sealed.



It marks 15- to 18-weeks of fetal growth with the fetus is approximately 16 cm and weighs about 320 gramsEars are distinct and clearly stand out from head. Intestinal tract has secretions called meconium and the fetus exhibits sucking and swallowing reflexes. Fetal movements may be felt by the mother in the form of quickening.



It ranges  between 19 to 22 weeks of fetal development where , fetus measures about 21 cm by the end. The  approximate weight at this phase is 630 grams.  Nipples are apparent on the breasts. Skin is covered with vernix caseosa ( a sticky material) and the entire body contains fine , silky hair called lanugo.  Skin is wrinkled and appears reddish with the brown fat found on the neck and sternum. Fats help in heat production and conservation.



It is the period between 23- 26-weeks  where the fetus measures  approximately 25 cm and weighs i kilogram by the end of the 25 weeks. Fingernails have reached the tip of fingers and the eyes partially open with eyelashes present. Lungs contain bronchioles  and the primitive alveoli. Skin begins to thicken on hands and feet. 



It is the period between 27- 30 weeks and the fetus measures 28 cm and weighs 1.7 kilograms by the end of 30 weeks.  Ample hair is formed on head at the same time, lanugo begins to fade. Skin slightly wrinkled and the toenails are clear. Testes are descended into the inguinal canal.



It comes in the weeks 31-  34 and the fetus measures 32 cm and weighs 2.5 kiligrams approximately.The skin becomes pink and smooth. The testes reach the scrotal sac.



It comes in 35-38 weeks  and rarely it extends to 40 weeks where the labour can initiate at any time between 36-40 week. fetus  measures 36 cm and weighs 3,400 grams but it may vary.There is ample subcutaneous fat and the lanugo is almost absent. Toenails reach toe tips . Testes are inside the 2 scrotal sacs.


Fetal growth chart indicating the growth parameters



Factors affecting fetal development

During the pregnancy, the mother’s health status plays a vital role in safeguarding the growth and development of the fetus. Right from the first day of conception, the mother must be screened regularly for dangerous signs to gain an understanding of the status of the fetus. At this stage, 2 lives need to be taken care, I,e mother and fetus, hence it is important to understand the possible signs of threat. Important factors influencing the growth of fetus are, mother`s dietary practices, rest and sleep, activity levels, genetic factors, culture and religious practices, habits and psychological or emotional environment in which she is present.

1. Genetic factors

Abnormal genes contribute to the IUGR (intrauterine growth restriction), some of the genetic disorders like inborn errors of metabolism, Rh factors, chromosomal disorders in the family can impede the normal development of the baby. It is important to collect a detailed history of family and genetics. Consanguineous marriages (marriages within the blood relations) must be excluded because genetic defects are common in this type of couple.

2. Nutritional factors

This is one of the most important factors which we can control because mother can decide the good and bad nutritional practices. A balanced nutrition containing the required proportion of proteins, vitamins, minerals, calories and fibre is very essential for the normal weight gain of the fetus. Mother’s weight must be regularly monitored to identify the signs of malnutrition. On an average mother gains 11.5 kilograms by the end of the pregnancy. The minimum calorie requirement during the pregnancy is 2800 kilocalories, nevertheless, it also depends upon the lifestyle and activity level of mother. Sufficient fluid intake in the form of water, tender coconut, juices, and semi-solid foods can help to maintain the hydration status of the mother.

3. Cultural factors

Cultural factors, religion and spiritualism are the important factors as they influence the health of both the mother and baby. In some families, cultural factors restrict the healthy practices, for instance many families restrict the intake of eggs during pregnancy but scientifically, eggs are very essential for the normal growth of the fetus.  

4. Mother’s habits

Healthy habits are really important as there is a proportional relationship between the mother's habits and the fetal health. Strictly inculcate the no smoking and no alcohol behaviour during the pregnancy as the substance abuse can seriously harm the baby in many ways. Majority of the birth defects in the baby are directly linked with maternal drug intake, alcohol consumption and smoking.

5. Emotional factors

Mother’s emotions must be under control. During the pregnancy, the family’s support is one of the major priority. A peaceful, affectionate, and harmonious relationship of the mother and family members is definitely a great plus for both mother and fetus.


6. Exercise, rest and sleep

A normal routine with a bit of caution ascertains the health and comfort of mother. There is no restriction on the day-to-day activities however, the activity level must be within the comfort zone of the mother. Lifting heavy loads is not advisable. 3o minutes of walk and meditation would definitely help in gaining control over the health of both fetus and mother. The average duration of sleep for a pregnant mother range 7-10 hours a day with a nap in the afternoon.


Read more


Evidences for evolution


Reproductive health


Pregnancy and placenta formation 





  1. What are the different phases of pregnancy?

  2. Explain the factors affecting fetal development.

  3. Brief the developmental changes during embryonic and fetal period.

  4. Why nutrition is important during the fetal development?


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