Third Trimester

The period between the 28th week to the 40th week (or the time of delivery) constitutes the third trimester of pregnancy. It is during these few months of the third trimester that a pregnant woman puts on quite some weight and also experiences many mood swings and myriad emotions. The foetus grows rapidly, and is fully developed during this period, as it prepares to function outside the mother’s womb, independently, post delivery.

Role of hormones during the third trimester of pregnancy
As the hormonal balance continues to fluctuate, a pregnant woman might suffer from an acne outbreak as the delivery time approaches. Due to hormonal changes and with the time of delivery nearing, the woman experiences a mixed feeling of excitement and anxiety. The third trimester is not only very tiring and uncomfortable for a woman but is also emotionally challenging.

During the third trimester, as the baby grows in the womb and the time of delivery approaches, a woman experiences a lot of changes.

  • Discomfort – The weight of the baby has increased substantially by now. The 50 gm uterus now holds the baby, placenta and around one litre of amniotic fluid. It is thus obvious that the lady experiences discomfort.
  • Heartburn – As the uterus stretches and grows in size, it exerts pressure on the intestines, which in turn exert pressure on the stomach. This often leads to heartburn.
  • Shortness of breath – The growing uterus also exerts some pressure on the diaphragm causing difficulty in breathing. But increase in the level of progesterone makes the woman to breathe deeply, thus maintaining the oxygen levels.
  • Leaking urine and frequent urination – The growing uterus exerts pressure on the urinary bladder as well. This results in urine leakage, and also a frequent need to urinate.
  • Difficulty in sleeping – As there is shortness of breath, increase in weight and discomfort it might become difficult to get a sound sleep during the third trimester.
  • Itchy skin – The skin over the abdomen stretches and tightens, thus causes itching during the third trimester.
  • Stretch marks – Stretch marks start to appear on the stomach and thighs, as the skin stretches to accommodate the growing foetus. They may also appear on the breasts, as breasts too enlarge and prepare for lactation.
  • Backache – Back pain may worsen during the third trimester, as the baby bump grows larger.

Role of placenta in the third trimester
During the third trimester the placenta allows maternal antibodies to pass through to the foetus. This helps the foetus develop a passive immunity against infections. The placenta also has a mechanism through which it prevents the mother’s body from attacking the foetus, which may be detected as a foreign body.

Changes during the third trimester of pregnancy- week by week

29th- 34th  week
The third trimester of pregnancy is the most crucial phase. During the initial part of this phase the baby grows to develop finer details like creases on the skin of the wrists and the palms. As a fat layer forms under the skin, the baby takes a more rounded form. During this period of the third trimester, testes in the male foetus descend down into the scrotum from the abdomen. Initially the heart of the foetus beats at the rate of 160 beats per minute. However, during this stage it decreases to 110 – 150 beats per minute. Lungs continue to develop and the cell lining of the lungs secretes a substance that helps the lungs to inflate when the baby breathes.

34th – 36th week
During this period of the third trimester the foetus is fully formed, as it prepares to live independently. The enzymes in the gut of the baby become active, thus enabling it to process food. The lanugo and the greasy vernix begin to disappear, and the skin is no more translucent. The baby now occupies all the space available in the womb, and wriggles inside, as it cannot make full fledged movements due to lack of space. Occasional hiccups and blinking of eyes by the baby is also possible.

37th – 40th week
This is the last phase of the third trimester and the baby now weighs around 3 kg and measures around 20 inches in length. At this stage the baby can blink, grasp with its tiny fists and turn its head. The baby can perform various activities and functions like breathing, swallowing, movements, etc. in a better way. The baby shows increased sensitivity towards touch from outside, sound, light, etc. The baby can also feel its mother’s emotions and anxiety. By the 40th week (as the end of the third trimester approaches) the baby’s growth is complete. It fills up the entire uterine space and positions itself in the mother’s lower abdomen. The foetus positions itself in such a way that the head is placed in the pelvic cavity as it prepares for birth. The labour phase starts during this week with uterine contractions and widening of the cervix after which the baby is born. In case the positioning is not as mentioned above a caesarian section becomes necessary.

Care during the third trimester of pregnancy

  • Continue the prenatal medications and vitamins as per your doctor’s prescriptions
  • Continue to avoid smoking, alcohol consumption or any other types of recreational drugs
  • Do not exert your body in any way
  • Keep yourself hydrated, and avoid hot baths and hot spa or saunas
  • Do not keep standing for too long
  • Make sure you take adequate rest
  • Continue with your healthy diet regimen of fibre rich foods. Have small, frequent meals
  • While you are sleeping, provide support to your legs with a foot rest or pillow
  • Avoid crossing your legs, or letting them hang while sitting
  • Do not try to lift heavy loads
  • Minor stretching and toning can be done to ease child birth

It is good to be prepared for the labour, which may begin any time during this phase. You need to assemble all the necessary things for your hospital stay, get your labour kit in place, and pack your hospital bag. Also start preparing for the baby’s arrival; you will have to buy all the post delivery necessities for you and your baby.

The weight of your brain is 2% of your total body weight. Brain uses 20-25% of the oxygen you breathe, and it needs around 15% of the total blood supply