What is the stages of embryo ( fetus ) development ?
The fetus development
the fertilization occurs about two weeks after the first day of the last menstrual period , when the sperm penetrates the egg , and within 24 hours after the fertilization , the egg begins dividing rapidly into many cells .
The fertilized egg remains in the fallopian tube for about three days , the fertilized egg (called a blastocyte) continues to divide , and it passes through the fallopian tube to the uterus to be implanted in its lining ( a process called the implantation ) .
The developing baby is called an embryo from the moment of conception to the eighth week of pregnancy , and after the eighth week and until the moment of birth , the developing baby is called a fetus .
What are the stages of embryo ( fetus ) development ?
The period of pregnancy ( 9 months ) can be divided into 4 main stages which are :
The first stage :
The first stage starts from the moment of zygote formation till the end of the sixth week , In this stage , the head starts to differentiate ( it is similar to the reptiles head ) , The eyes appear distinctly , In the sixth week , the heart can be seen and heard pulsating using the sonar .
The second stage :
The second stage starts from the beginning of the seventh week till the end of the twelfth week , In this stage , the facial features can be distinguished , the genital organs start to develop and the appearance of the digits in the limbs .
The third stage :
The third stage starts from the beginning of the 13th week till the end of the 22th week , In this stage , the bones start to develop , as well as the circulatory system , the sex of the embryo can be distinguished , and the mother can feel the movement of her fetus due to the strength of the embryo muscles which help in the movement .
The fourth stage :
The fourth stage starts from the beginning of the 23th week till the delivery ( the birth ) , In this stage , the development of all body systems is completed , the embryo can move his hands and feet .
Before the delivery , the embryo position changes gradually to be inverted , where the head is directed towards the cervix , The baby can be born in the 28th week , where his two lungs are able to respire and all systems are completely developed .