The fetal development timeline traces the events that take place as an embryo grows into a fetus, which eventually grows into a full term baby. Given below are details regarding this timeline according to the week wise progression of pregnancy.
The word ‘fetus’ signifies the developing mammal after the embryonic stage until just before birth. An embryo on the other hand is considered to be the time span from fertilization up till two months after fertilization. The fetal development timeline traces the events which occurs during this stage. This is the main stage when things can go wrong, as the end of the first trimester is a crucial phase where there is further growth and development of vital organs.
Learning about the fetal development timeline will help the expectant mother to plan out her schedules, diets, and also to follow the doctors instructions regarding the pregnancy more easily. This will in turn help to increase the baby’s chances of survival and also prevent it from contracting any health complications in the mothers stomach.
Timeline of Fetal Development
|Week 1 – Week 2||This is generally one to fourteen days from the last menstruation. Fertilization is still in process.|
|Week 3||There is fertilization of the ovum to form the zygote. The zygote undergoes mitotic cellular division, but does not increase in size. There is implantation of the embryo onto the endometrial lining of the uterus.|
|Week 4||Trophoblast cells surrounding the embryonic cells proliferate and invade deeper into the uterine lining. There is formation of yolk sac, primitive streak and primary stem villi.|
|Week 5||A notocord forms in the center of the embryonic disc and a neural groove forms over the notocord. A primitive heart tube also starts forming.|
|Week 6||The embryo measures around 4mm and begins to bend to form a ‘C’ shape. The heart bulges and begins to beat. The neural tube closes and the ears begin to form as otic pits. First traits of lungs, liver, and spleen appears.|
|Week 7||The embryo measures 8mm in length. Lens pits and nasal pits form. The brain divides into five vesicles and leg buds are also seen. Rudimentary blood moves through primitive vessels.|
|Week 8||The embryo measures 13mm in length. The brain continues to develop and the lungs begin to form. Lymphatic system also begins to develop.|
|Week 9||The embryo measures around 18mm in length. Hair follicles and nipples begin to form. Most of the essential organs have begun formation. At times, spontaneous limb movements can be detected with the help of ultrasound.|
|Week 10 – Week 12||The embryo measures 30mm in length. Facial features start to develop. The head comprises nearly half of the fetus size. Tooth buds appear and the face is well formed. The limbs are long and red blood cells are produced in the liver.|
|Week 13 – Week 16||The fetus reaches a length of 15cm. The fetus makes active movements and sucking motions are made with the mouth. Fine hair called lanugo develops on the head.|
|Week 19||The fetus reaches a length of 20 cm. Eyebrows and eyelashes appear and the entire body is covered by lanugo.|
|Week 23||The fetus reaches a length of 28 cm. All the eye components are developed. The heart, liver, and spleen are already functioning at this stage. The fetus has a hand and startle reflex at this stage. Alveoli are forming in the lungs.|
|Week 27||The fetus reaches a length of 38 cm. The brain develops rapidly and the eyelids can open and close.|
|Week 31||The length of the fetus is around 38 cm. The amount of body fat starts increasing rapidly and rhythmic breathing movements are seen. Bones are fully developed and the fetus begins to store iron, calcium, and phosphorus.|
|Week 35||The fetus reaches a length of around 40 to 48 cm. The lanugo begins to disappear and body fat continues to increase. By the end of this week, if a baby is born, then it has high chances of survival, but it may require medical intervention.|
|Week 36 – Week 39||The fetus is considered to be full term by the end of the 37th week. It may be 48 to 53 cm in length. Head hair is now coarse and thick. This stage eventually transcends into child development stages after the birth of the baby. The size of the brain however, continues to grow without multiplication of neurons. This is because the brain and lungs are the last organs to develop completely.|
It is extremely important for an expectant mother to be knowledgeable of this fetal development timeline as this is the main stage at which she needs to be extra careful so as to ensure proper development of her baby’s body and organs.
Disclaimer: This HerHaleness article is for informative purposes only, and should not be used as a replacement for expert medical advice.