7 weeks pregnant: Changes for baby

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How big is your baby now?

Your baby is growing quickly! At the beginning of this week your baby is 4-6mm long. Over the next few days your baby will almost double their height to be 6-9mm long by the end of this week! That is about the width of a regular paper clip.

How is your baby’s appearance changing?

Body shape

Most noticeable in your baby this week is the continued growth of its head. It’s a very important change, as your baby’s head growth is driven by the growth of its brain – as the brain grows larger, the head must also grow to accommodate it.

Last week, the shape of your baby’s body changed considerably and took on the c-shaped curve which is typical of a foetus. As baby’s head grows this week, the face moves and comes into contact with a bulge in the hollow of the c-shaped curve which will grow into your baby’s heart.

Facial features

Small cup-like structures which will eventually house baby’s eyes also form this week, and the lens of baby’s eye (lens placodes) which appeared in pregnancy week 6 continues to develop. They attach to the hyaloid artery which supplies their blood. Your baby’s eyes and nose also take on a more distinctive appearance. Pits which will grow into baby’s nostrils form and bulge out slightly from the face. A groove which separates the eyes and nose, and a bulge which will later become baby’s forehead also become distinct this week. The developing structures of the nose attach to other tissues in the face region to form the structure of the cheeks.

Baby’s ear canals and external ears are also developing further this week. The ear canals look like tiny hollow tubes and the external ears are, at this stage, just three small mounds on each side of the developing neck. The beginnings of the ear canal and external ear grow from the first pharyngeal arch which also forms your baby’s jaw bone. But the jaw bone still has lots of growing to do- it is not until around the 16th week of pregnancy that the jaw bone grows sufficiently to push the ears into their proper position at the side of baby’s head.

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The upper and lower limb buds, which will grow into your baby’s arms and legs also continue to grow this week. The upper limb buds (arms) become paddle shaped and grow larger (but it’s not until you are 10 weeks pregnant that these ‘paddles’ will become distinct hands and fingers). The lower limb buds also grow longer and have a flipper-like appearance (but proper toes will not be formed until you are 10 weeks pregnant).Arteries which supply blood to the developing arms and legs also begin to form and develop further as the limbs lengthen. Nerves which will control the arm and leg muscles and movements also begin their development in week 7 of pregnancy.

How are your baby’s internal organs developing?

Your baby’s internal organs, which began developing last week continue developing this week.

Brain and nervous system

Your baby’s brain increases rapidly in size this week. By the beginning of this week, the brain has divided into three sections, the forebrain, midbrain and hindbrain.Twelve pairs of nerves which attach directly to the brain (they’re called cranial nerves) begin to develop this week and continue their development next week (when you are 8 weeks pregnant). They include the nerves which will control movement of baby’s eyes, tongue, face and throat, and provide a sense of smell (supply the olfactory senses). These nerves are part of what is known as the peripheral nervous system. The peripheral nervous system controls all conscious movements.

Nerves which form the sympathetic nervous system control involuntary (unconscious) body movements like the heart beating. The sympathetic nervous system also begins to develop this week.

It is also this week that baby’s spinal nerves begin to form. Some of the cells from the somites (from which baby’s vertebrae will develop) move into the structure which will form baby’s diaphragm (an organ of the respiratory system which works with the lungs to regulate breathing) this week. As the somites move, they pull nerve fibres with them. The nerve fibres become the phrenic nerves, that is, the nerves which supply your baby’s diaphragm. Other somites develop further to form the neural tube (the structure which will eventually from baby’s central nervous system including the spinal cord and brain).

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Urogenital system

The urogenital system includes the genitals and all the organs involved in the making and excreting urine. The urinary organs begin to form this week. Two structures known as the mesonephric ridges have formed by the beginning of this week. They will go on to form the mesonephric kidneys, which produce urine on a temporary basis until your baby’s permanent kidneys develop (when you are 11 weeks pregnant). A tiny structure known as the ureteric bud appears from these mesonephric kidneys; it will eventually grow into baby’s urethra (the tube which the wee comes out of). It grows rapidly in the next four weeks and forms connections with lots of tiny tubes which allow urine enter the urethra. A structure which will grow into baby’s bladder also begins developing this week.

The sex organs (gonads) also begin to form this week, however it is not yet possible to determine whether you are carrying a baby girl or boy. In the initial stages of development the sex organs are undifferentiated, that is they are the same for boys and girls. This week a ridge, called the gonadal ridge, forms. Depending on the sex of your baby, it will either grow into baby’s vagina, clitoris and ovaries, or into a penis, scrotum and testes.

Lungs and airways

Two bronchial buds, which will grow to form your baby’s lungs and bronchi (airways), begin to grow in a structure called the pleural cavity at the beginning of this week. At this stage, the pleural cavity which contains the lungs, is still connected by two channels called pericardioperitoneal canals, to the pericardial cavity, which contains baby’s heart. These channels will close to form separate cavities for the heart and lungs in coming weeks. Other organs of your baby’s respiratory system, including the upper food pipe (pharynx) and wind pipe (trachea) begin to form later this week. These muscular tubes which will transport food to baby’s stomach and air to its lungs form between the pharyngeal arches which will grow into baby’s jaws and facial structures.

Cardiovascular system and blood vessels

The aorta, the major artery that carries blood away from the heart, is visible this week and connects to the tube-like structure which will grow into your baby’s heart. Interim veins (the posterior cardinal veins) connect to the mesonephric kidneys, and will later disappear as the mesonephric kidneys (also temporary) are replaced by the permanent kidneys. New veins grow to supply the pharyngeal arches, which will develop into facial structures and neck as your baby develops.

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Baby’s developing heart pumps blood through these arteries and veins and the blood moves between your baby’s tiny body and the placenta, via the umbilical veins. This exchange of blood is essential to ensure baby’s blood contains enough oxygen. As baby’s lungs have not yet begun to function, blood takes in oxygen from the placenta (which connects to and receives oxygen from your body) and distributes this through baby’s body. The heart also changes structure this week as walls grow to partition the heart into four sections (the bulbus cordis, ventricle, atrium and sinus venosus), whereas previously it was a single chamber.

Endocrine system (glands which produce hormones)

The first of the body’s hormone producing glands to develop is the thyroid gland, which is eventually positioned in the neck and produces hormones involved in digestion. It began as a structure known as the thyroid primoridium about half way through last week, at which stage it was a hollow between the first and second pharyngeal arches. This week the hollow structure becomes a solid mass of cells, separated by a hollow tube into right and left sections. The pancreas, another gland which produces digestive hormones and is also part of the gastrointestinal system also begins to form this week.

Gastrointestinal system

Baby’s tongue, which first appeared as three areas of swelling (a middle, left and right side swelling) between the pharyngeal arches towards the end of last week, begins to grow rapidly this week. The left and right swellings grow most quickly, and eventually grow over the middle swelling and merge together to form a single tongue.

Towards the end of this week your baby’s oesophagus (the muscular tube which will transport food to your baby’s stomach) begins to form. It is only short at this week, but will grow rapidly in the next two weeks and reach its final length when you are 9 weeks pregnant. The abdominal wall and a small pouch which will grow into baby’s stomach also begin to form.

Other gastrointestinal organs which begin to form this week include the:

  • Duodenum (first section of the small intestine) which begins as a small loop below the pouch which will grow into baby’s stomach;
  • Pancreas (a hormone-producing gland in the abdomen) begins to form this week but will not begin functioning to produce the hormone which regulates blood sugar levels (insulin) for several more weeks;
  • Thyroid gland (a hormone producing gland in the neck);
  • Liver (an organ which detoxifies the body from substances like alcohol and medicine) which grows rapidly from now until you are 12 weeks pregnant and in these weeks it takes up a lot of the space in baby’s still tiny abdominal cavity. The liver is not yet functioning, but will begin to do so next week;
  • Bile ducts (which produce secretions that help digest food); and
  • Gall bladder (a digestive organ which plays an important role in digesting fat); and
  • Spleen (which functions as part of the lymphatic system).


Baby’s bones also undergo further development this week, with the beginnings of the humeral bones (which will eventually connect baby’s shoulders and elbows). Bones which will form baby’s legs do not begin to grow until after the embryonic period, when you are 12 weeks pregnant. Baby’s vertebrae, which began developing as somites when you were 5 weeks pregnent continue to develop this week.

How are the placenta and foetal membranes forming?

Umbilical cord

The umbilical cord which connects your baby to the placenta (which in turn connects baby to your body and allows it to exchange nutrients, gases and waste products) becomes visible this week. It consists of a single vein and two arteries. The vein carries blood and nutrients from your body to your baby and these are returned to your body via the two arteries.

The umbilical vesicle

The umbilical vesicle, also called the yolk sac, is an important structure which facilitates the transfer of nutrients from your body to your baby’s body in early pregnancy. It can be seen from when you are 5 weeks pregnant with sonography and until the end of the first trimester it is distinguishable by ultrasound. At about 32 days after fertilisation, the umbilical vesicle is large. However, it begins to shrink after 7 weeks and by the time you are 22 weeks pregnant it is usually too small to be seen.


More information about week 7 of pregnancy

120002144 Happy couple For more information about the seventh week of pregnancy, see 7 weeks pregnant.
56460615 Woman laughing For more information about the changes going on in mum’s body this week, see 7 weeks pregnant: Changes for mum.
114274104 Woman at doctor's For more information about pregnancy health in the seventh week of pregnancy, see Doctor appointments and health information this week.
154021786 Couple using tablet For a summary of the key points about the seventh week of pregnancy, see 7 weeks pregnant: Key points.
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Date Created: February 4, 2013