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A​​fter conception and throughout the course of your pregnancy, your baby goes through various phases of growth and development as it implants into the womb and matures into a full term foetus. 

Your pregnancy can be generally divided into three main phases: 

These periods are important as varying stages of fetal development are present in each of the trimesters. The symptoms that you may experience are different. However, this is just a guide and each pregnancy could be different. 

​​First Trim​e​ster​: Week 1 - 6

Baby development ​

This is still considered the embryonic stage. It arises just after fertilisation of the egg and subsequent implantation of the embryo into the womb lining. The various structures of your baby are not yet fully developed. 

As the weeks pass: 

  • ​The outer layers of the fertilised egg (known as the outer cell mass) will form the eventual placenta

  • The inner layers of the fertilised egg (known as the inner cell mass) will give rise to the brain, lungs, central nervous and intestinal systems​ ​



​​​​This is a period whereby the developing organs are highly sensitive to teratogens (drugs affecting the development of baby). Major defects may be produced during this period should there be an exposure to these teratogens. By the end of week 6, the embryo measures about 4 - 5 mm and the heart starts to beat and can be detected on a scan at the end of this stage. 

Your symptoms

You may feel absolutely fine and the first clue to your pregnancy could be the fact that you just missed your period. It is crucial that you consult your doctor if you are taking any long-term medications. 

​First Trimester: Week 6 - 12

Baby development 

The baby can now be considered a foetus and this stage is a time of rapid growth. The various vital organs are formed as the body straightens. 

By week 12, most of the major organ systems would have been developed and the baby, known as a foetus, takes on a more recognisable form. It measures about 6 cm from head to buttocks. 

The following changes are observed: 

  • ​​The head is also growing to accommodate the enlarging brain.

  • The eyelids are present in the shape of folds and by the end of week 12, they will meet and fuse, remaining closed until the end of month 6.

  • The external genitalia are also well differentiated at the end of this stage.

  • The limbs continue to develop, and nails appear on the digits. The moving limbs can be visualised but the movements cannot be felt until a few weeks later. 

After week 16, the baby is less likely to be sensitive to the detrimental effects of teratogens as most of the organs would have developed. 



Your symptoms

Your pregnancy hormones will begin to rise by now. You may start to experience the unmistakable early symptoms of pregnancy such as morning sickness, breast tenderness and fatigue. Your urine pregnancy test will definitely be positive by now.​

Second Trime​s​​ter​: Week 13 - 16

Baby development 

The baby continues to grow in size. The proportion of growth is such that the head is still considerably larger than the body. 

With the continued development of the genitalia, the gender may be discernable by the end of this stage. 

The limbs are now fully developed and can move vigorously at times. 

Your symptoms 

By now, the early symptoms would have lessened and your appetite starts to return. Your weight would also begin to increase gradually. Your breasts will continue to enlarge and your nipples will darken. 

Your womb would have risen out of your pelvis by now and can be felt on palpation of your abdomen. The baby’s heart beat can also be obtained through a doptone machine placed on the womb.​ 

Second Trimester: Week 17 - 24

Baby development 

The baby continues to grow and mature. Hair on the head develops while fine hairs on the body (lanugo) appear. 



Your symptoms 

Your physical discomforts of the pregnancy will start to show. They may include the appearance of stretch marks, backaches and a sensation of shortness of breath and palpitations, owing to the enlarging womb. 

A screening scan should be performed at around 20–22 weeks to exclude any structural abnormalities. You may even begin to feel the baby’s movements —​ known as "quickening".

Second Trimester: Week 25 - 28

Baby development 

The eyelids open and the eye lens can be seen. After 24 weeks, the baby is considered by many to be potentially viable. With modern advanced neonatal care, the baby delivered prematurely between 24–28 weeks of pregnancy has a fairly good chance of survival. By the end of 28 weeks, the baby should weigh about 1 kg. 

Your symptoms 

Your physical discomforts, as described above, will continue to worsen and varicose veins may also begin to appear on your legs. Sleeping at night may start to trouble you. It is important to find your own sleeping position to make yourself comfortable. Having a support for your tummy as you lie on your side to prevent any compression on your major blood vessels may be a good idea.

Third Trimester​: Week 29 - 34

Baby development 

The lanugo hairs on the body start to disappear and the skin becomes more pinkish. Fat beneath the skin accumulates and the fetus appears rounder. The fetal movements are more varied now and may alternate between a state of rest and active moving. Babies born after 34 weeks have a very good prognosis.

​Your symptoms 

Your tummy feels taut and you may begin to feel irregular painless tightenings over your womb. These are also known as "Braxton-Hicks" contractions and are usually insignificant if there is no associated show or leaking liquor. Your baby becomes considerably heavier and your backache and fatigue may increase. 

You may also be experiencing shortness of breath as the enlarging womb presses against your rib cage. At times, the sudden movements of the baby may be painful and the moving limbs may be felt from the surface of your tummy. Contrary to what most mothers think, your baby is actually still very comfortable in the womb despite the increase in size. 

Heartburn may increase due to the enlarging womb and reduction in gastric movements. The milk glands in your breasts have started to produce colostrum. This provides nutrition to the baby in the breast milk​. At this stage, your breasts may even leak colostrum.

​Third Trimester: Week 35 - 40 

Baby development 

By now, the baby has fully formed and the head is more proportionate when compared to the size of his body. The lanugo hairs would have completely disappeared and the skin smoothened out. As the expected due date approaches, the head will begin to descend into the pelvis -- a phenomenon known as "engagement". The baby’s weight continues to increase such that it usually weighs more than 2.5 kg at the time of delivery. 

Your symptoms 

With the increasing weight of your baby, the aches and pains from the ligament stretch in your pelvis will increase. The lower abdominal aches and urination from the pressure on the bladder can be troubling. From 37 weeks onwards, your baby is considered fully matured (full term) and labour contractions can begin at any time. However, in 10% of women, preterm labour may happen before 37 weeks. 


Acknowledgement

Source: Dr TAN Thiam Chye, Dr TAN Kim Teng, Dr TAN Heng Hao, Dr TEE Chee Seng John, The New Art and Science of Pregnancy and Childbirth, World Scientific 2008. ​