Understanding Your Pregnancy’s First Trimester

Pregnancy is a beautiful journey lasting approximately 40 weeks, or a little over nine months when you count from the last menstrual period to delivery. This period of 40 weeks can be divided into three trimesters, each offering its own unique experiences and milestones.

Entering the first trimester, you may experience a whirlwind of emotions—ranging from pure joy to occasional bouts of apprehension. Let us understand more about what to expect during these initial weeks and how to navigate this transformative phase.

Duration of the First Trimester in Pregnancy

A woman's due date is typically calculated by adding 40 weeks to the first day of her last menstrual period. The first trimester spans approximately 12 weeks, beginning on the first day of the last menstrual period and continuing until the 12th week of pregnancy.

Foetus Development During the First Trimester

The first trimester is fundamental to the development of the foetus’ major organs and bodily systems.

1st to 4th week	For first-time pregnancies, your baby bump may not be visible until around week 12. If you have been pregnant before, your baby bump may show earlier because your uterus’ muscles may have already been stretched from your previous pregnancy. Your baby (embryonic stage) measures about 2mm in length, which is roughly the size of a poppy seed. An amniotic sac filled with fluid surrounds the embryo, keeping it safe and sound. A tiny yolk sac is attached to this sac, providing all the nourishment your baby needs to grow. As the embryo continues to develop, the outer layer of the sac transforms into the placenta, a vital organ that delivers oxygen and nutrients to your growing baby.
5th to 8th week	Facial features including a small nose and little eyes are beginning to develop. The eyes would stay closed until around week 28. Other rapid growth includes baby’s brain and spinal cord. A collection of the baby’s own network of blood vessels forms the umbilical cord that delivers essential nutrients and oxygen from the placenta to the baby, while also eliminating waste products. By the eighth week, the embryo measures approximately 16mm, comparable in size to a raspberry. The miniature head is beginning to straighten out slightly. The upper body undergoes more rapid growth compared to the lower body. The arms are elongating, and the legs are also extending. However, specific features like the knees, ankles, thighs, and toes have yet to form. The embryo now transitions into a “foetus” around this time.
9th to 12th week	The foetus now measures approximately 5.4 cm from head to bottom, comparable in size to a plum. Heartbeat is detectable through ultrasound scans. Internal organs and muscles have matured significantly, and the skeletal structure is transitioning from soft tissue to hardened bone. The sex organs have taken shape. However, it may still be challenging to determine the gender via ultrasound scans at this stage. Further development is needed before it becomes clearer.

Common Symptoms During the First Trimester

During the first trimester, you will experience a number of physical changes to your body. Hormonal changes during pregnancy may trigger specific symptoms, such as nausea or vomiting (morning sickness), which is pretty common, breast tenderness, frequent urination, headaches, lower back and pelvic pain, heartburn, weight gain or loss, constipation, food cravings, and mood swings.

Tips for Expectant Mothers

Schedule an initial prenatal visit with your obstetrician as soon as possible once you find out you are pregnant. During this first prenatal visit, your obstetrician will discuss about establishing your expected delivery date. An ultrasound, blood and urine tests may be conducted.

Ask your obstetrician about antenatal screening, which is vital in ensuring a healthy pregnancy.

If prenatal vitamins are recommended, do follow your obstetrician’s advice as prenatal vitamins are crucial for supporting your baby’s development.

Adjust your diet to ensure both you and your baby receive adequate nutrition during pregnancy, focusing on consuming a balanced and wholesome diet. Avoid raw fish (sushi), uncooked or undercooked meats, and unpasteurised milk, cheese, or juice.

Follow your obstetrician’s guidelines in terms of staying physically active during the first trimester. Safe, low-impact exercises are generally helpful to maintain your fitness during pregnancy while prioritising your baby’s well-being. Avoid contact sports and activities that put pressure on your abdomen.

Other than that, it is advisable to stop smoking, avoid alcohol or illegal drug use, reduce your daily caffeine intake, and avoid hot tubs and saunas.

For more information, read our comprehensive guide to prenatal care and find out what to expect in the second trimester and third trimester of your pregnancy journey.

Make an Appointment at Gleneagles Hospitals

If you have questions about prenatal care during your pregnancy, get in touch with us to book an appointment today for a consultation, or visit our Obstetrics and Gynaecology Department at your nearest Gleneagles Hospital

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