Stage Fetal Development Week by Week
Every expectant mother wants to know absolutely everything about her baby. Future moms want to monitor their babies’ development week by week. It is very important for a pregnant woman to know everything about the intrauterine growth of the baby, monitor the development of the ears, learn when the baby starts blinking, how he sleeps and why he is pulling.
First Trimester (1-13 Weeks)
3-4 Weeks Pregnant
The baby's head is already formed. The heart, legs and arms are under formation. Ultrasound can show that circulation is already set. The brain and spinal cord begin to form.
4-6 Weeks Pregnant
The heart is already dividing into four chambers. Fingers and toes are forming. Reflex activity begins with the development of the brain and nervous system. You can already see the eyes, jaw, ears. The liver, stomach and lungs are forming.
6-8 Weeks Pregnant
All the important parts of the body are already present; however, they are not fully formed.
Ears, eyes, legs and arms are perfectly visible. Then begin to form muscles and the skeleton. The nervous system is improving.
8-10 Weeks Pregnant
Nails appear on the fingers and toes. The baby can already move in the womb. However, these movements are unnoticeable for the mother. A special fetal stethoscope allows checking the baby’s heartbeat. All the important organs are present. Muscles are developing.
10-13 Weeks Pregnant
The baby starts swallowing, the kidneys produce urine, bones start producing blood cells. Fully formed muscles allow the baby to make a wide range of movements. The baby’s eyelids are formed. You can already learn the baby’s sex.
Second Trimester (14-26 Weeks)
14-16 Weeks Pregnant
The head, arms and legs are already formed. The fetal skin is transparent. The baby’s head starts covering with hair. Movements become more coordinated.
16-18 Weeks Pregnant
The skin has a pink color; you can clearly see ears, all parts of the body, the baby’s face. The baby can blink, grab, and open the mouth. He starts pulling actively in the womb.
18-20 Weeks Pregnant
All the organs are already formed, and there begins the next stage – they begin to grow. The skin is covered with a special protective lubricant. Breathing movements occur, but they are weak to fulfill the normal lung function. At this term, the expectant mom can feel her baby moving. An ultrasound scan can show the baby’s sex.
20-22 Weeks Pregnant
The fingers are developing; hair starts growing on both the head and the body. The baby sucks a thumb and makes more movements. At this term, the brain is developing rapidly. The fetal heartbeat can be checked with a stethoscope. The kidneys start functioning. However, born at this term, the baby has small chances to survive outside the mother’s womb.
22-26 Weeks Pregnant
Begins the ossification of the ear bones that are able to hear sounds now. The fetus can already hear his mom: her heartbeat, breath and voice. Fat deposits are forming. The baby is putting on weight actively. The lungs are enough developed, which allows the baby survive outside the mom’s body in an intensive care ward. However, premature babies can have organ functioning disorders. This means that they must stay for a long time in an intensive therapy.
Third Trimester (27-42 Weeks)
27-28 Weeks Pregnant
The baby reacts to both intrauterine sounds and external sounds. Reflex movements are improving, the body is growing stronger. The lungs continue to develop. The baby is now able to fall asleep and to wake up. The skin becomes red and features a wrinkled structure and thin hairs. Eight out of ten babies born at this term survive in intensive care wards.
29-30 Weeks Pregnant
The lips and the mouth have an increased sensitivity. The eyes can open and perceive light. Brain impulses are the same as in full-term infants. Nine out of ten babies born at this term survive in intensive care wards.
31-32 Weeks Pregnant
Lungs can breathe normal air; however, there is still a need of medical assistance. The baby can open and close the eyes, suck a thumb, cry and react to external sounds. The brain (CNS) controls the body temperature and rhythmic breathing. Almost all babies born at this term survive with the help of medical staff.
33-34 Weeks Pregnant
The skin thickens and becomes pinkish. The number of contacts between nerve cells in the brain increases. Starting with this term, the baby starts to grow rapidly. Almost all babies born at this time survive thanks to the doctors.
35-36 Weeks Pregnant
The ears got their normal shape. When the baby is awake, his eyes are open; when he falls asleep, he closes his eyes. The baby’s skin is smooth and pink. Almost all the babies born in this period survive (and only few need medical assistance).
37-38 Weeks Pregnant
The baby can sleep with closed eyes, the ears are fully shaped. Hair becomes silky. The baby can turn and raise his head.
39-40 Weeks Pregnant
The lungs are fully formed, the grasp reflex is very pronounced, and the baby reacts to light. The fetus makes about 70 automatic reflex movements. They are necessary for survival. The baby is about 50 cm (20’) long and weighs about 2500-4000g (5,5-9 lb).
41-42 Weeks Pregnant
The baby is ready to be born.