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Fetal Development - Stages of Pregnancy Week by Week

Fetal development is an intricate and orderly process that begins before you know you have conceived. The baby's birth takes place at the end of this wonderful journey. Between conception and childbirth, the fetus goes through three stages of development. Read below to learn more about fetal development by week.

Book an online appointment with Dr. Priyamvada Shah for Pregnancy & Gynecology related issues

When Does Pregnancy Start, and How Long Does it Last?

The first day of the last period is the start of the pregnancy. It is the gestational age, which is two weeks more than when conception happens. So, the first day of the last period is essential to determining the due date. The length of the pregnancy is nine months. However, this may be different for some. A full-term pregnancy is 280 days or 40 weeks, but it can be shorter or longer and is healthy and completely normal.

Stages of Pregnancy Week-by-week

The first three months of pregnancy are the 'getting ready’ phase. The body releases pregnancy hormones, and the uterus prepares for potential pregnancy. By the second week, ovulation happens, and if the sperm and egg meet, the pregnancy continues.

Week 3: Fertilisation happens, and a zygote is created.

Week 4: The cells become blastocysts and are implanted into the uterine lining. An amniotic sac that provides a cushion to the fetus is formed. By the end of this week, the blastocyst is about 2 mm long.

Week 5: The spinal cord, brain, and central nervous system neural tissues are formed. The tiny heart tube at this period will beat 110/60 seconds by the end of this week.

Week 6: Legs and arms are developed. Blood circulation begins, and structures that later become mouth, ears and eyes take shape. Heartbeats can be detected on vaginal ultrasound.

Week 7: Gentials begin to form, and the embryo resembles a tadpole.

Week 8: All body systems and major organs are formed. Ears begin to take shape, and eyes are visible. The umbilical cord is developed and transports blood and oxygen to the embryo.

Week 9: The taste buds are formed, the teeth begin to shape, and the body gets a human appearance. The heartbeat is audible to an ultrasound.

Week 10: Feet, toes, arms, fingers and hands are formed. Toenails and fingernails develop, and external ears take shape.

Week 11: The fetus's ankles and elbows begin working, and the fetus starts exploring. The bones get hard, but the skin is transparent. Facial features can be seen prominently.

Week 12: The muscles, bones, limbs and organs develop and function. The liver creates bile, and the digestive, circulatory and urinary systems also work. The fetus is peeing and drinking amniotic fluid. By this time, the fetus is about 3 inches long.

Week 13: The head becomes proportional to the body, and vocal cords are formed.

Week 14: Fine hair starts to grow, and the fetus's skin thickens. Fingerprints start to form, and the external genitals are formed. The fetus can turn its head and also put fingers into the mouth.

Week 15: Organs like ears and intestines move to the permanent location. The lungs start to develop, and the fetus makes more movements.

Week 16: The ears and lips are developed, and the fetus can hear you speak. The eyes may be closed, but the fetus can react to light and turn away. By the end of this week, the fetus will be 5 inches long.

Week 17: The skin starts to put on fat, and it has a coating called vernix to protect it from amniotic fluid.

Week 18: The fetus is covered by fuzz-like hair called lanugo for protection and warmth. If asleep, it gets disturbed by loud noises.

Week 19: The mother begins to feel punches and kicks. The fetus has its unique fingerprints.

Week 20: The fingernails grow, and the part of the brain responsible for the five senses starts to develop. By the end of this week, the fetus weighs 1 pound.

Week 21: Limb movements become more frequent and coordinated. Bone marrow that produces blood cells develops.

Week 22: The fetus can touch the umbilical cord and its ears. It can hear your breathing and your heartbeat.

Week 23: The fetus, if born prematurely, can survive after this time but with intensive care.

Week 24: The lungs are fully formed but can work outside the uterus. By the end of this time, the fetus weighs about 2 pounds.

Week 25: Body fat makes the skin plump and less wrinkled. The nervous system matures.

Week 26: The fetus produces melanin, which colours the eyes and skin. The lungs produce surfactant, which helps to breathe.

Week 27: The fetus can open its eyes, blink, and have eyelashes.

Week 28: The fetus begins to turn in the uterus and is ready for birth. At the end of this, the fetus weighs about 2-3 pounds and is 14-15 inches tall.

Week 29: The fetus is cramped and may feel more pokes.

Week 30: The brain matures, grows rapidly, and can control its body heat.

Week 31: The fetus can process information and stimuli. You may notice their sleep patterns.

Week 32: The skin becomes thicker, and the brain, lungs, and other organs are developed and ready for birth. The baby weighs about 5 pounds and is 17-18 inches long.

Week 33: The bones are harder, except the brain, which has to be soft to go through the birth canal.

Week 34: The vernix becomes thicker.

Week 35: The brain continues to grow and weighs two-thirds of what it should weigh at birth.

Week 36: The fetus sheds its lanugo and has head hair. It is now 6-7 pounds and 17-19 inches tall.

Week 37: The toenails are formed, and you may feel the fetus come down to the pelvis.

Week 38: The fetus is growing and adding weight to become its final size.

Week 39: The full-term is completed, and the fetus is ready to come out.

Week 40: This is your week of the due date, and you should notice labour signs. The fetus weighs about 7-9 pounds and is about 18-20 inches long.

A lot happens during pregnancy, week by week, and learning how the fetus grows is exciting and eye-opening, as it showcases the miracle of nature. You and your fetus go through many changes during this time; ask your healthcare provider if you have any questions about it.

Also Read : How To Survive The Longest Stage Of Pregnancy – The Final Two Weeks


1. In which week fetus is fully developed?

31 weeks into pregnancy, the fetus is fully developed.

2. What is the most important week of fetal development?

The first 5 to 14 weeks of pregnancy is the most important period of fetal development.

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