At last the third and final trimester!  The third trimester is from weeks 28 – 40.  This last trimester can become uncomfortable for the mother as her baby continues to grow, in preparation for birth.

Body changes

Body changes mothers may experience during the third trimester include:

• disturbed sleep
• more obvious Braxton-Hicks contractions
• difficulty breathing
• standing with feet wider apart
• waddling when walking

Postural changes

For some women their posture will have changed from midway through their pregnancy and may stay the same through the third trimester.  For other women the third trimester will see an increase in the curve of their lower back (lumbar spine), or their body may adopt a ’swayback’ posture where their lower spine stays the same but they lean their shoulders back.  If the curve in the lower back increases the weight of the growing baby is carried on the pubic bones at the front of the pelvis and by the abdominal muscles.  For women whose bodies adopt the swayback posture, the weight from the baby, is carried behind the pubic bones and puts more pressure on the pelvic floor muscles and the pelvic ligaments. 

To counterbalance the weight of the expanding abdomen pulling them forwards, most women will move their head and neck backwards.  The middle of the spine (thoracic spine) will often flatten its usual curve.

It usually feels much more difficult to breathe deeply as the uterus is sitting just below the respiratory diaphragm (the main muscle that you use to breathe).  The lower ribs spread outwards to make some more room and this also tends to pull the diaphragm muscle fibres tighter as well as changing the amount the ribs are able to expand as you breathe.

It is quite common to feel as though you are waddling when walking during the third trimester (and sometimes earlier).  Your legs will turn outwards to allow space for your expanding abdomen.  You may notice you are standing and walking with your feet wider apart so that you feel balanced as your body adapts to your changing centre of gravity.  Some pregnant women may experience sciatica, a sharp pain down the back of the thigh, that is caused by one of the nerves of the thigh being squashed as it travels down the leg.  Osteopathic treatment may be beneficial in reducing discomfort from sciatica during pregnancy.

Your feet may feel sore and may also become wider due to the relaxin hormone in your system that loosens your ligaments in preparation for birth.  It is common to put more weight on the outer part of the feet during the third trimester as the legs turn outwards, and you might find it beneficial to relax with your feet up when you can.

Baby changes

During the third trimester your baby is preparing for being born.  The brain and nervous system are developing rapidly.  Your baby now breathes at the same rhythm they will breathe once born and the lungs become covered with special cells and fluid (surfactant) to prevent the air sacs in the lungs from collapsing when your baby breathes air for the first time. 

Your baby’s skin is now pink due to the layer of fat underneath it that will help to regulate body temperature and provide energy after birth.  The skin is covered in the waxy vernix caseosa that will protect your baby’s skin and provide lubrication during birth.  By 34 weeks your baby can focus their eyes and blink.

Your baby will have a lot less room to move about in now, and will gradually stop moving about as much (unless you happen to be in a position that doesn’t suit baby).  Some babies will move into a head down position (engage) around 34 weeks, most will engage after 36 weeks.  By 38 weeks your baby is fully developed and just waiting for the right time to be born.

By 40 weeks your baby will have grown to be about 35 – 37 cm long and will weigh 3 – 4 kg.

Feeling pain?

If you are feeling pain or discomfort during your pregnancy, osteopathic treatment may be of benefit.  Osteopathic treatment is gentle and safe throughout pregnancy, and may help the body to adapt to the changes that are occurring in the musculoskeletal system, so that you can feel more comfortable.

You may also be interested in "Body Changes During the 1st Trimester of Pregnancy" or "Body Changes During the 2nd Trimester of Pregnancy"

This articles was written by Dr. Alison Neilson B.App.Sc. (Comp.Med.), M.Ost. of Renew Osteopathy, Mornington 

If you are interested to learn more about Osteopathy read Alison's article in our Practitioner Profile section - Osteopathy

References

Stone C. Visceral and Obstetric Osteopathy. Philadelphia: Churchill Livingstone, Elsevier, 2007. Ch 10.

Bullock JE, Jull GA, Bullock MI. The Relationship of Low Back Pain to Postural Changes During Pregnancy. The Australian Journal of Physiotherapy. 1987;33(1):10-17.

Moore K, Dumas GA, Reid JG. Postural changes associated with pregnancy and their relationship with low-back pain. Clinical Biomechanics 1990;3:169-174.

Stoppard M. Conception, pregnancy and birth. Victoria: Dorling Kindersley, 2002.