Fetal Development & Baby Growth During Pregnancy Breaking Down Pregnancy Week by Week

Congratulations! You are about to embark on the beautiful journey of becoming a mother and giving birth to your baby. The next nine months are going to be extremely exciting and you will go through a lot of emotional and physical changes in your body.

Fetal development takes about 40 weeks and is usually divided into three trimesters. The first trimester is the first 13 weeks of pregnancy; the second trimester is week 14 to week 27; and the last trimester are the last stretch of week 28 to week 40. In this article we will cover the first trimester of pregnancy, and the baby growth during pregnancy as the weeks go by. This will help you prepare for what to expect as you go through the pregnancy week by week for fetal development. 

Fetal Development during First Trimester of Pregnancy

The first trimester of pregnancy covers the 13 weeks of your pregnancy.

 At 4 weeks:

From now on, till 10 weeks, all the baby’s organs begin to develop and some begin to function. The fertilised ovum (called the embryo) now burrows into the womb and separates into cells that will become the placenta and baby. The layers of the embryo start differentiating into specialized parts. The outer layer will become the baby's hair, skin, eyes and nervous system; the middle layer will soon be the heart, reproductive organs, bones, muscles and kidneys; and the inner layer into the baby's liver, lung and digestive system. This is the time when the baby is most vulnerable to any interference with development. The sac in which the baby is housed (amniotic sac) is also formed. This is the time for confirmation of the pregnancy.

At 5 weeks:

At the beginning of this week, the embryo already has 125,000 cells, is growing rapidly in the uterus and looks like a tadpole. The neural tube from which the brain, spinal cord and nerves develop is starting to form. Skin, hair, tooth enamel, nails, mammary glands and sweat glands also begin to develop. Heart and circulatory system begin to divide into chambers and starts beating. The muscles, bone, cartilage, thyroid, liver, pancreas and digestive tract all begin to develop. In all, the baby is tube like and has what appears to be a head, back, front and tail. The tail disappears as the baby takes form.

At 6 weeks:

The embryo is growing rapidly. Nose, mouth and ears begin to develop. The baby will have an over-sized head and dark spots where eyes and nostrils form. Depressions at the side of the head are the ears and protruding buds are the limbs. The embryo is growing an umbilical cord which is its life line to get nutrients and oxygen from the mother. 

At 7 weeks:

The embryo looks like a tadpole at the beginning of the 7th week but by the end of the week it begins to look somewhat human. Body continues to lengthen; hands and feet are beginning to emerge from the limbs. Eyelids start to form and baby’s brain is growing rapidly. The liver has started producing red blood cells which goes on until the bone marrow develops. By the end of the week, the embryo’s whole skeleton made of flexible cartilage is formed. Other organs like digestive system, liver, heart, spleen and appendix start to form. The placenta is represented by hundreds of hair like projections which makes it look like a hairy ball.

8 weeks:

The baby looks more human now. The face is becoming clearly defined. Eyelids are forming and nose starts to protrude. The upper lip is beginning to take shape. The breathing tube starts to grow from the throat to the branches developing in the lungs. The genitals are not yet clear. Fingers and toes start to form. The heart is now beating. 

9 weeks:

The heart chambers are formed and valves begin to develop. The baby’s teeth begin to form. Though external genitalia are beginning to develop the sex is not discernible. The eyes are fully formed but eyelids are fused. The baby has tiny earlobes and the mouth, nose and nostrils are distinct. The placenta has taken over the basic functions of the baby, like supplying oxygen and nutrients. 

10 weeks:

All cells are directed to their places. The baby is now capable of swallowing liquids and organs like liver, kidney, intestines and brain have started functioning. The webbing of the fingers and toes have gone and nails and hair start growing. The baby can bend his joints. The spine outline is visible and spinal nerves start to grow. 

11 weeks: 

Tooth buds appear on the gums and bones begin to harden. Diaphragm starts to form. Baby starts to move actively. The head is nearly half the body size. Part of the baby’s small intestine, coils around the umbilical cord outside the baby’s body.

 12 weeks:

The nervous system is continuing to grow and brain structure is fully formed. Reflexes start now. The baby can clench the fist, curl toes and make sucking movements. The intestines are growing rapidly and are now neatly tucked inside the body. The baby can pass urine. The thyroid begins to secrete hormones.

 13 weeks:

The embryo is now a foetus, which looks more like a human. Whorls begin to appear on finger tips. Veins and organs are visible through the transparent skin. If the baby is a girl, she now has over 2 million eggs in the ovaries. The foetus can move its arms and legs.

Tags: Pregnancy Week by Week , Fetal Development , First Trimester of Pregnancy , Baby Growth During Pregnancy


Was this article helpful?

© 2016 Columbia Asia