Development of your baby

2nd Trimester

The structure of the baby is now pretty much complete and the 2nd trimester (second 13 week period) is a time of rapid growth. This is the period at which ultrasound is at its best in visualising the baby and the time that most people will start to feel movement. 

Throughout the Second Trimester, we can undertake ultrasound examination to monitor the pregnancy (13 - 34 wk Reassurance Scan). NOTE: Although the genitals are now formed, it is too early to identify the fetal sex by ultrasound.

Week 14

Astonishingly, the baby's eyebrows and lashes start to grow now, and the eyes, which were formed on the side of the head, have moved to the front. Likewise, the ears, which formed close to neck level, are moving up to the head. The intestines are developing folds to absorb nutrients and the kidneys are now producing urine, which the bladder releases into the amniotic fluid. The thyroid gland has now matured and is producing thyroid hormones. The baby now weighs 45g (1.6 ounces) and is 9cm in length from crown to rump.

Week 15

The baby's body is now growing fast, as if trying to catch up with the now developed head. The eyes are still tightly closed beneath sealed eyelids, but may begin to be sensitive to the filtered light reaching through the uterine wall. The genitals are fully developed and the baby's skeletal system and muscles continues to develop.

Week 16

The bones are beginning to harden (ossify) and tiny nails appear. Blood vessels show through the translucent skin, which is now covered in fine, downy hair called 'Lanugos'. By now, your baby weighs110 grams (about the same as a small pot of yoghurt) and is about 12cm in length. It can now hold its head erect and the facial muscles have developed sufficiently for the baby to squint, frown and make other facial expressions.

At week 16 onwards, we can undertake an ultrasound examination to determine the fetal gender (13 - 36 wk Gender Scan). NOTE: Determination of the fetal sex by ultrasound is NOT guaranteed in any way.

Week 17

With plenty of room to kick and roll around, your baby is very active. If you haven't felt it move yet, you are likely to in the next few days or weeks. The baby measures 13cm from top to tail, and is about 140 grams in weight.

Week 18

Now the big forehead and eyes are sensitive to light. The ears have reached their final position either side of the head and the baby's hearing is sufficiently good for responding to loud noises and can now hear your heart beating, as a result of development of the bones of the middle ear and the nerve endings. The baby is actively moving; performing turns, rolls & somersaults, and generally trying out different positions inside you.

Week 19

Permanent teeth are forming buds behind the milk teeth buds in the jaw. Arms and legs are now in the same proportion that they will be at birth. As nerves and muscles develop, control is being gained over movements such as bending the elbow and the knee. 'Brown fat' is now being laid down around the kidneys, chest and the back of the neck, to help regulate the baby's temperature in the first weeks after birth.

Between 19 and 24 weeks, we can undertake ultrasound examination to look for structural abnormality in the baby - or to reassure you that none are apparent (19 - 24 wk Anomaly Scan).

Week 20

Halfway gone - Halfway there!

The skin is starting to thicken into four layers and a creamy, moisturising, substance called 'Vernix Caseosa' covers it; which helps prevent the delicate skin from becoming chapped or scratched. At approximately 25cm from top to foot, (16cm, crown to rump), and a weight of about 312 grams, the baby is now taking up an increasing proportion of the available space in the uterus and starting to put pressure on your bladder and stomach. If you go for a scan this week you'll be able to see your baby for yourself.

Week 21

As well as supplying nourishment and oxygen via the placenta, you are also transferring antibodies from your blood to your baby, to protect from infection during the early months of life. Taste buds are forming on the tongue, and the baby now has the ability to absorb water and sugars from the amniotic fluid, which is swallowed and passed through the digestive system to the large bowel. Until now your baby's liver and spleen have been responsible for the production of blood cells, but now the bone marrow spaces are developed enough to contribute to blood cell formation as well, and bone marrow will become the primary site of blood cell production in the third trimester and after birth. (The spleen will stop producing blood cells by week 30, and the liver will stop a few weeks before birth.)

Week 22

Your baby can now look from side to side, hear loud music or shouting, and distinguish sweet tastes from bitter ones. Nerve endings are formed enough for the baby to have the sense of touch. The baby's reproductive system continues to develop; in boys the testes begin to descend from the abdomen and in girls the uterus and ovaries are in place. You might well feel the baby doing acrobatics just as you're dropping off to sleep, possibly because you breathe more deeply when you are resting, with the result that the oxygen supply to your baby increases.

Week 23

Your baby now looks very much how they will look when born; although the skin is quite red and wrinkled, more fat stores will be laid down over the next few weeks to plump it out. It currently weighs about 500 grams. You might be able to see and feel when you baby makes large movements.

Week 24

The vital organs are now mature, except the lungs which are not ready to cope with independent breathing, although they have now started developing the ability to produce a substance called "surfactant", which helps keep the air sacs in the lungs from collapsing and sticking together when the baby breaths out. So, if you went into labour now your baby would need intensive neonatal care, but any baby born at or after 24 weeks is considered 'viable' because it has a reasonable chance of surviving. Your baby's taste buds are developing. Its brain is growing very quickly, and its hair may be growing, too. Because the inner ear - which controls balance in the body - is now completely developed, your baby may be able to tell when it is upside down or right side up while floating and making movements in the amniotic fluid. It is now 28- 29cm long and weighs just over 500g.

Between 24 - 34 weeks, we can undertake ultrasound examination to monitor the growth of the baby (24 -34 wk Growth Scan).

 Week 25

The baby's movements mean that you can probably now tell when your baby is asleep or awake, and may be able to feel a little hand or foot pressing against your tummy at times. Thumb sucking may now occur and it has already developed a preference for using the right or left hand. It is possible for your baby to now even recognise your voice.

Week 26

The thickened skin, looks smoother and more opaque. The eyelashes have formed and your baby should be able to open its eyes this week. Virtually all babies are born with blue or dark blue eyes and it may not be some weeks after birth that they become the colour they'll stay. It weighs a little less than 2 pounds (900 grams), still looks wrinkly but will continue to gain weight steadily over the next 14 weeks until birth.




Back to Read about Fetal Development in the First Trimester


                                          Read about Fetal Development in the Third Trimester


See full details of Beehive Solutions Antenatal scans