The Third Trimester of Pregnancy

Published on: October 10, 2021

The final leg of the journey, the third trimester, is perhaps the most exciting and challenging time during pregnancy. But while you are waiting for your little bundle of joy, there are some things you should know. Emma McNerlin talks to us about these things.

By Emma McNerlin

The third trimester of pregnancy is defined as week 29 to week 40 (and beyond, in some cases). While preparing to meet your baby, there is often an urge to “nest”, to prepare a space for the baby. This is not based on biology but rather a psychological need to exert control over the birth environment (Anderson and Rutherford, 2013). Nesting is a vital part of preparing for birth. During this time, focusing on being as informed and prepared as possible for your labour, birth and beyond with some good quality local childbirth education to ensure the information is relevant to Thailand, is a healthy practice. Around 32 weeks is a great time to attend classes. There are lots of approaches available such as hypnobirthing and traditional childbirth education, both online and in person. You may have hired a doula who will support you and help you to prepare a birth plan, which your OB/GYN will discuss with you formally around your 36th week.

The third trimester is the most physically challenging time in pregnancy. As your body changes to accommodate your growing baby, your organs are put under increased pressure. Breathlessness can be caused by decreased lung capacity; gastric symptoms such as heartburn are due to hormonal changes driven by the pregnancy. By the third trimester, you should also be sleeping on your side to avoid the weight of the baby from pressing on the artery carrying blood to the placenta. Sleeping on your side will also encourage baby into a good position for birth.

You may need to urinate more often and even find yourself experiencing some sporadic leaking of urine. The weight of pregnancy also puts extra strain on your pelvic floor muscles. Hence, it is important to get into the habit of doing your pelvic floor exercises, or Kegels, regularly throughout pregnancy to avoid stress incontinence later. It is never too late to start them, and much like motherhood, you may find yourself doing them for life! 

Weight gain in the latter part of pregnancy changes your gait and increases the curve at the base of the spine. Known as lordosis, this can cause back pain and pain around the hips and buttocks. If you experience constant pain in your pelvic region (especially at the front), this can be an indicator of pelvic girdle pain (PGP). This is caused by an increase in the hormone ‘relaxin’ as the ligaments supporting the pelvis become softer in preparation for birth. Your doctor may refer you for physiotherapy and prescribe a pregnancy support belt to lift the weight of the bump off your pelvis (NHS, 2019).

 By 29 weeks you should be aware of your baby’s pattern of movements throughout the day. Any reduction of movements or change in the pattern should be reported to your doctor and investigated. If you are concerned at all about movements, always have it checked out. Some doctors will advise counting a discrete number of kicks in a day (between 10 and 20), but the best evidence indicates that it is the pattern of movement that is most reliable (

In the third trimester you can also expect to see your doctor more often. From around 32 weeks you will see your OB/GYN every two weeks, and from 37 weeks they will see you every week until your baby arrives. Most OBs will offer an ultrasound scan at each appointment. You can discuss the clinical need for any interventions with your doctor at these appointments. At 32 weeks, a scan will confirm your baby’s position, hopefully head down, the amniotic fluid levels, and the location of the placenta. The doctor may also check placental function if they are concerned about the baby’s size.

 Braxton Hicks Contractions (BHC) increase in frequency and strength in the third trimester. This is  completely normal and a healthy sign that your body is preparing for birth. Oestrogen is developing oxytocin receptors in the uterus and the Braxton Hicks help indicate where the receptors should be. They also help baby to prepare for the stress of labour. BHC are localized and uncoordinated, and do not cause any changes to your cervix. Dehydration can cause increased BHC so make sure to maintain healthy fluid levels.

 Ever wondered why your doctor asks for a urine sample at each appointment? They are screening for protein, which, when accompanied with high blood pressure, indicates pre-eclampsia (PET). This is a serious pregnancy condition that affects 2–8% of pregnancies worldwide (March of Dimes, 2021). PET usually manifests in the last month of pregnancy, but in severe cases can happen from 20 weeks. Using blood tests, doctors can now measure Placental Growth Factor (PlGF) from 20 weeks onwards to help deduce increased risk of developing pre-eclampsia. This helps in providing early treatment if needed. If you develop PET, your doctor will discuss your treatment with you. For more information on PET, see:

 Your doctor may also repeat some blood tests in the third trimester at around 36 weeks. A complete blood count (CBC) will indicate if you are anemic. In the last weeks of pregnancy, babies take the iron they need for their first six months of life from their mother. Anemia can cause dizziness and breathlessness, and extreme fatigue. It can also increase the risk of post-partum haemorrhage. Anemia is treated with iron tablets or, in severe cases, an iron infusion.

At 36 weeks you will also be offered a test to screen for Group B Strep (GBS), a bacterial colonization carried by around 25% of women which is usually harmless. However, 1 in 200 babies born to GBS positive mothers will go on to develop a potentially fatal GBS infection. Detecting GBS in late pregnancy means that you can receive antibiotics during labour to cut the chance of your baby getting the infection to 1 in 40,000 (

 There is a lot of local support available if you have questions about birthing in Bangkok, including BAMBI’s Bumps Team and the Doulas of Bangkok, who can help to signpost you to relevant help should you need it.

***The contents of this article are intended for informational use only and should not be considered as medical advice. If you are concerned about any aspect of your pregnancy, please consult your OB/GYN. ***

Photos from Canva.


Anderson, M. and Rutherford M.D. 2013.  Evidence of a nesting psychology during human pregnancy in Evolution and Human Behaviour Vol 34 (6) available online at: 2021. Pelvic pain in pregnancy. [online] Available at: <> [Accessed 6 September 2021].

Kicks Count. 2021. How often should I feel my baby move?. [online] Available at: <> [Accessed 6 September 2021].

McEvoy, A. and Sabir, S., 2021. Physiology, Pregnancy Contractions. [online] Available at: <> [Accessed 6 September 2021].

Action on Pre-eclampsia. 2021. What is pre-eclampsia – Action on Pre-eclampsia Information. [online] Available at: <> [Accessed 6 September 2021].

Hypertension. 2021. PlGF (Placental Growth Factor) Testing in Clinical Practice: Evidence From a Canadian Tertiary Maternity Referral Center. [online] Available at: <,pregnancy%2C%20or%20fetal%20growth%20restriction.> [Accessed 6 September 2021].

Group B Strep Support, 2021. [online] Available at: [Accessed 6 September 2021].

March of Dimes, 2021. Preeclampsia. [online] Available at: [Accessed 6 September 2021].

About the Author

Emma McNerlin is a UK-trained and registered Midwife, First Aid Instructor and owner of Bumpsy Daisy Café and Community; a cafe and parenting community centre for new and expecting parents offering birthing classes, hypnobirthing, First Aid workshops and baby classes.

The views expressed in the articles in this magazine are not necessarily those of BAMBI committee members and we assume no responsibility for them or their effects. BAMBI welcomes volunteer contributors to our magazine. Please contact