The Fetal Stages of Human Development

Here, Joanna's medical illustrations show the development of the human foetus week by week. The start of life called the embryonic period, is followed by this the fetal period which starts at the 8th week of development through to birth. The fetal period is characterized by the growth and maturation of tissues and organs that have formed during the embryonic period. Although the foetus is still the size of a kidney bean at 8 weeks measuring 1.6cm, the organs and muscles and nerves are beginning to function. Rapid growth will continue especially between week 9 to 20. All these developments are included in the medical illustrations as below to provide a week by week visual story. For a full illustrated view on embryonic development, click here.

Dating Your Pregnancy

The actual exact age of a developing foetus and the due date of a baby's birth given to an expectant mother, differs by approximately two weeks. These medical illustrations of the foetus are dated from the actual day of fertilisation. A womans's pregnancy dates differ because it is not possible to know exactly when a womans egg was fertilised, plus there are also several days around ovulation when fertilisation could have taken place. So a GP will estimate the length of the pregnancy using the dates of the last period, or menstrual cycle. Therefore, pregnancy is calculated using the date of the first day of the period, which means a woman will be considered to be 4 weeks pregnant by the time the next period has been missed. The actual foetus however, which had been fertilized right at the start of ovulation, has already been developing for approximately two weeks, although for the first seven days it would only have been a collection of dividing cells.

Foetus development at 8 weeks

Foetus development at 8 weeks

Foetus development at 9 weeks

 

Foetus development at 9 weeks

Foetus development at 10 weeks

Foetus development at 10 weeks

 

Foetus development at 11 weeks

Foetus development at 11 weeks

Foetus development at 12 weeks

 

Foetus development at 12 weeks

Foetus development at 13 weeks

Foetus development at 13 weeks

 

Foetus development at 14 weeks

Foetus development at 14 weeks

Foetus development at 15 weeks

 

Foetus development at 15 weeks

Foetus development at 16 weeks

Foetus development at 16 weeks

 

Foetus development at 17 weeks

Foetus development at 17 weeks

Foetus development at 18 weeks

 

Foetus development at 18 weeks

Foetus development at 19 weeks

Foetus development at 19 weeks

 

 

Foetus development at 20 weeks

Foetus development at 21 weeks

Foetus development at 22 weeks

 

Fertilisation

Fertilisation occurs when a males sperm fertilises a woman's egg or ovum, taking place inside one of the fallopian tubes. Fertilisation is completed when the nuclei of the egg and sperm have combined, creating a single cell that is then capable of further development by dividing into further cells. The journey of the fertilised egg carries along the fallopian tube for about four days, where by the single cells has been dividing until it is a ball of cells surrounding a fuid filled hollow called a Blastocyst. Upon reaching the uterus or womb, this Blastocyst is ready to attach itself to the uterus wall, which has already formed a spongy lining. The embyro burries itself into the wall of the uterus untill it is fully covered. It is here the embryo will develop, forming a placenta to gain nutrients to grow.

 

Foetus development at week 1

Foetus development at week 2

Foetus development at week 3