Pregnancy by weeks

Pregnancy by Weeks

You may be interested to know what’s happening in the abdomen during pregnancy. This article will explain the development of the baby throughout each week of pregnancy.

Pregnancy period (gestational age)

The period between the last menstrual cycle and the childbirth is known as the pregnancy period. Usually, it lasts about 40 weeks.

Gestation period

The period between the conception and the childbirth is the gestation period. Gestation period is about 38 weeks.

Embryonic period and foetal period

The period up to the end of the eight weeks of gestation is called the embryonic period. The foetal period starts from the end of the embryonic period and lasts about 30 weeks.


The embryonic period

Fifth week of pregnancy (third week of gestation)

  • Central nervous system, (the brain and the spinal cord) and the heart start to develop.
  • Development of the digestive system starts during the fifth week of pregnancy.


Sixth and seventh weeks of pregnancy (fourth and fifth weeks of gestation)

  • The eyes and ears start their development.
  • Buds of the limb (the arms, and legs) are visible now.
  • The brain and some cranial nerves grow further.
  • Initial development of the back bones (vertebrae) and other bones occurs.
  • The heart grows further and beats regularly. Immature blood flows through major blood vessels.


Eighth week of pregnancy (sixth week of gestation)

  • The lungs start their development.
  • The brain grows further.
  • The buds of limbs grow longer.
  • The hands, feet, fingers, and toes are visible now.


Ninth week of pregnancy (seventh week of gestation)

  • All organ systems have started their development at this stage.
  • Elbows may be visible.
  • Hair and the nipple development start.


Tenth week of pregnancy (eighth week of gestation)

  • Visible part of the external ear starts its development to original shape.
  • The eyelids and other facial features grow further.
  • The bowels rotate.


The foetal period

11th to 14th weeks of pregnancy (ninth to 12th week of gestation)

  • The liver produces red blood cells.
  • Facial features are well-developed.
  • The baby can clench the fists.
  • Tooth buds start their development.
  • The baby will close the eyes and will not reopen until 28 weeks.
  • The genitals can be differentiated.
  • The baby has long and thin limbs.
  • The size of the head is about half of the baby.


15th to 18th weeks of pregnancy (13th to 16th week of gestation)

  • The baby moves actively.
  • Fine ‘lanugo hair’ appears on the scalp.
  • The gastrointestinal tract forms the earliest stools (meconium).
  • The bones and muscles develop gradually.
  • The pancreas and the liver make secretions.
  • The skin is transparent at this stage.
  • The baby can make sucking movements.


19th to 21st weeks of pregnancy (17th to the 19th week of gestation)

  • The baby moves more actively and can hear sounds.
  • The mother can feel wavelike motion in the lower abdomen.


22nd week of pregnancy (20th week of gestation)

  • Eyebrows, eyelashes, Fingernails and toenails appear.
  • Gradual muscle development helps the baby move more actively.
  • The mother can feel the movements of the baby.
  • Fine ‘lanugo hair’ appears over the entire body.
  • The baby’s heartbeat can be detected by auscultation.


23rd to 25th weeks of pregnancy (21st to 23rd weeks of gestation)

  • Fat tissues of the baby start to store fat.
  • Bone marrow produces blood cells.
  • The lower airways of the lungs develop gradually.


26th week of pregnancy (24th week of gestation)

  • Fingerprints and footprints are developing.
  • The baby has well-formed hands.
  • The baby has the startle reflex.
  • Eye parts, eyebrows, and eyelashes are well-developed now.
  • The air sacs of the lungs develop.

Startle reflex: If the baby feels a sense of falling or hears a loud noise, he will straighten out the arms, legs, open the fingers and curve the back. Then the baby will squeeze the fists and pull the arms to his chest.


27th to 30th weeks of pregnancy (25th to 28th weeks of gestation)

  • The baby opens the eyes during this period.
  • The baby can shut and open the eyelids.
  • Despite the respiratory system is still immature, the lungs have developed enough to exchange gases.
  • The central nervous system can control some functions of the body.
  • The brain develops rapidly.


31st to 34th weeks of pregnancy (29th to 32nd weeks of gestation)

  • The baby starts storing calcium, iron, and phosphorus.
  • The baby has well-developed, soft, and flexible bones.
  • The amount of body fat is increased rapidly during this period.
  • The lungs are not well-developed.
  • The baby has rhythmical breathing movements.
  • The fingernails are well-developed.


35th to 36th weeks of pregnancy (33rd to 34th weeks of gestation)

  • The lungs are almost well-developed now.
  • Reflexes of the baby are well-coordinated.
  • The mother may feel contractions of the abdomen.


38th week of pregnancy (36th week of gestation)

  • The baby has smooth skin due to underlying fat layer.
  • Fine lanugo hair disappears gradually.
  • The baby may reach its birth position in this stage.


39th to 42nd weeks of pregnancy (37th to 40th weeks of gestation)

  • The baby has small breast buds.
  • The scalp hair becomes thicker and coarse.
  • The nails grow beyond the fingertips.
  • Fine lanugo hair remains on the arms and shoulders.
  • The baby is fully developed now and ready to go.
  • Congratulations!


(Photo courtesy: Teza Harinaivo Ramiandrisoa)

Related Links:

Symptoms and Diagnosis of Pregnancy
How a Baby Is Conceived?
Manage Your Weight During Pregnancy
Benefits of Exercise During Pregnancy and Cautions

About the author
Dr. Nalaka Priyantha is the founder and author of 'DRN Health'. He currently works at the Ministry of Health, Sri Lanka as a senior medical officer. He is blogging about healthy living since 2012.
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