Pregnancy – A Tale of Three Trimesters: Part One

Published on: June 08, 2021

In a three-part series, midwife Emma discusses what to expect in your pregnancy and typical obstetric healthcare in Bangkok. This month focuses on the first trimester of pregnancy.

By Emma McNerlin

Congratulations! You’re pregnant! One of the first things to establish is when your baby is due. Pregnancy is traditionally dated from the first day of the last menstrual period. Your due date is provisionally confirmed 280 days (or 40 weeks) from this date. Commonly referred to as Naegelé’s rule, this was the main method of dating pregnancies before obstetric ultrasound (Myles, 2020). However, Naegelé’s rule is problematic as it assumes a 28-day cycle, but only 13% of women experience this (Hutchon and Ahmed, 2003). Assisted conceptions are dated 38 weeks from implantation. 

Between 10 and 12 weeks, your doctor will conduct a dating ultrasound scan to give you an official due date. This is calculated from the crown-rump length, a measurement from the crown of the head to the bottom of the buttocks. In the first trimester, growth is standardized, so the due date should not be adjusted later in pregnancy when growth is affected by maternal diet and lifestyle factors. We know that only 4% of babies arrive on their due date (Mongelli, 2016), and in an uncomplicated pregnancy, labour can safely start anytime from week 37 to week 42.

Choosing your obstetrician can be daunting, especially if you are not familiar with the private obstetric-led model of care followed here in Thailand. Seeking advice in social media groups on “the best” obstetrician is tempting; however, it is incredibly subjective. Knowing the type of birth you want can help to narrow the search. You can change doctors and even hospitals at any point in your pregnancy should you want to. For impartial help and advice on choosing a doctor, contact The Doulas of Bangkok through Facebook. If you have not already started to take pregnancy vitamin supplements, your obstetrician can provide them. Folate or folic acid are important to help prevent neural tube defects such as spina bifida (Pitkin 2007).

You will be offered blood tests around week 10, including: CBC (complete blood count), blood group and antibody screen, serology tests for hepatitis B, syphilis, HIV, and for immunity to rubella. Although rare, these conditions can impact care plans for your pregnancy, so it is advised to rule them out. Most hospitals also offer NIPT (noninvasive prenatal screening), a simple maternal blood test to screen for chromosomal abnormality. The NIPT does not provide a diagnosis, rather an individualized risk of your baby having a trisomy condition. If you screen as high risk, you will be offered further diagnostic testing. This screening will also confirm the sex of your baby, so if you are choosing not to find out, please ensure this is not disclosed on the report. The cost of the NIPT can be prohibitive, especially if you are uninsured. A lower-cost option is a slightly less sensitive screening test (78% vs avg. 95% for NIPT: NHS 2021) known as the triple test.  If you have questions about screening tests, discuss them with your doctor. 

Traditionally, pregnancies have been kept secret by the expectant parents in the first 12 weeks because of the increased risk of pregnancy loss, with 80% of all miscarriages occurring during this period (Cohain 2017). Pregnant couples may carry anxiety and worry about the pregnancy that they do not share with friends and family. Pregnancy symptoms including nausea and sickness, breast tenderness and fatigue can be debilitating in the first trimester. Being unable to reach out for help can compound the worry and stress.  In truth, there is no right or wrong in this situation, and each person should be able to disclose their pregnancy at the time that is right for them. Should they suffer a miscarriage, they may find that support from the people they told will help them cope better with the loss, rather than trying to carry on in silence. 

Hormonal shifts which sustain the pregnancy are responsible for adverse and overwhelming pregnancy symptoms. Progesterone is responsible for tiredness, bloating and constipation, while oestrogen is responsible for the heightened sense of smell, and HCG causes breast tenderness and nausea/sickness. In most cases, nausea and tender breasts subside early in the second trimester. If symptoms are debilitating, you should consult your doctor, who can prescribe vitamin B6 and zinc. Acupressure bands and some herbal remedies can also help. Between 0.5 to 2% of women suffer from hyperemesis gravidarum, a severe form of pregnancy sickness which persists throughout pregnancy (Karger, 2017). These cases may require IV hydration and anti-sickness medication. 

In pregnancy, there are steps you can take to keep yourself healthy. Eat a healthy balanced diet, and avoid raw or undercooked meats, fish, and eggs, and unpasteurized dairy products. Avoid foods that are high in vitamin A, along with shellfish and deep-sea fish. You can continue to exercise throughout your pregnancy to alleviate some minor disorders. Time for rest is also important. 

In the first trimester, those unpleasant symptoms can be weirdly reassuring as physical proof that your baby is growing and thriving. Many pregnant couples welcome the 12-week milestone and the beginning of the second trimester of pregnancy with relief and excitement. Most see an improvement in symptoms, and the famed pregnancy bloom begins. 


Hutchon D.J.R. & Ahmed F. (2003) Naegele’s Rule: An Appraisal British Journal of Obstetrics and Gynaecology. [Online at:]  

Myles, M. (2020) A Textbook for Midwives. Elsevier Press.  Mongelli, M. (2016) Evaluation of Gestation. [Online at:]  

Pitkin, R. (2007) Folate and Neural Tube Defects. [Online at:]  Screening tests in Pregnancy (2021) NHS Choices Booklet  

Cohain, J. (2017) Spontaneous First Trimester Miscarriage Rates. [Online at:]

The information contained in this article is intended for informational purposes only and should not be considered as medical advice. If you have any concerns regarding your health or your pregnancy, please consult your doctor.

Photo from Canva

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. When she is not working she enjoys baking, aqua-aerobics and singing badly at karaoke.

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