Week-by-Week Foetal Development: What to Expect at Each Stage

Pregnancy is an incredible journey filled with rapid changes happening to the mother’s body as well as the baby’s. Each week brings new developments, with the baby progressing from a tiny embryo to a fully formed newborn. This blog will guide you through the foetal development week by week, highlighting what to expect at each stage. Understanding what happens in the womb can help expectant mothers feel more informed and confident about the changes taking place.

First Trimester

Weeks 1-4

The first weeks of pregnancy begin with conception, when the sperm fertilises the egg. The fertilised egg, now called a zygote, travels down the fallopian tube and implants itself into the lining of the uterus. During this time, the baby’s cells begin dividing rapidly. At the end of week 4, the embryo is only about the size of a poppy seed. Early symptoms like fatigue, nausea, and frequent urination may begin as the body starts adjusting to hormonal changes.

Weeks 5-8

In these weeks, the baby’s organs start forming. The heart begins to beat, and the brain, spinal cord, and other vital organs begin developing. The baby’s limbs start to take shape, with tiny arm and leg buds visible. By week 8, the embryo is now referred to as a foetus, and major facial features, including the eyes and mouth, begin to form. Many women experience more pronounced pregnancy symptoms, such as morning sickness and mood swings, during this stage.

Weeks 9-12

By week 9, the baby’s organs, including the liver and kidneys, start functioning. The baby’s face becomes more defined, with eyelids, ears, and nose developing further. Fingernails and toenails also start to form. As the first trimester nears its end, the risk of miscarriage decreases significantly, and many women begin to feel a bit better as nausea and fatigue start to subside. The baby is now fully recognisable as a tiny human, with limbs, eyes, and a rapidly developing nervous system.

Second Trimester

Weeks 13-26

During these weeks, the baby grows quickly. The tiny features are becoming more pronounced, and fine hair, called lanugo, starts covering the baby’s body. The baby’s ability to swallow and taste develops, and their movements, although still small, become more coordinated. The mother may start noticing a slight bump as the uterus grows, and she may feel more energetic as symptoms like morning sickness start to ease.

Weeks 17-20

By week 17, the baby’s hearing begins to develop, and they can start responding to sounds from the outside world. The mother may start feeling the baby move, which is known as "quickening." By week 20, the baby’s facial features become more recognisable, and the eyes start to open and blink. The baby is also developing a layer of fat under the skin, which will help them regulate body temperature. This is also when many expectant mothers undergo their mid-pregnancy scan, which checks the baby’s development.

Weeks 21-24

The baby continues to grow rapidly, with more noticeable growth spurts. Their bones become stronger, and they develop more muscle tone. Baby’s sleep-wake cycles also begin, and they may be more active at certain times of the day. The skin, still wrinkled, becomes less translucent as fat builds up beneath it. The mother may notice more back pain and leg cramps due to the increased weight and changes in posture.

Weeks 25-26

At this stage, the baby is continuing to gain weight and develop the fat layers needed for birth. The lungs and respiratory system are maturing, although they are not fully developed yet. The baby starts to practice breathing movements, which will be crucial after birth. The mother may experience more frequent, mild contractions known as Braxton Hicks, as the body starts preparing for the final stretch of pregnancy. Swelling in the feet and hands may also occur due to the increased pressure on the circulatory system.

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Third Trimester

Weeks 27-30

The baby’s brain continues to develop rapidly, and the nervous system becomes more refined. By week 28, the baby’s eyes can open and close, and they can even detect light. The baby’s movements become stronger and more pronounced, and they start to show more regular sleep-wake patterns. The lungs are developing, though they are still immature. The mother may feel more physical discomfort as the baby grows and the body adjusts, with increased back pain and swelling in the legs and feet.

Weeks 31-34

During this period, the baby’s lungs and immune system continue to mature, making it better prepared for life outside the womb. The baby is gaining weight, with the accumulation of fat making their skin smoother and plumper. The baby is more active, and the mother may feel stronger, more frequent movements. The uterus expands, causing more pressure on the mother’s organs, which can lead to shortness of breath and frequent urination. Braxton Hicks contractions may become more noticeable as the body prepares for labour.

Weeks 35-37

At this stage, the baby moves into the head-down position, preparing for birth. The baby’s body is filling out, with fat deposits increasing around the face, thighs, and arms. The baby’s kidneys are fully functional, and they begin to pass meconium (their first stool). The mother may experience increased pelvic pressure as the baby drops lower in the abdomen. The body begins to prepare for labour, and some mothers may notice an increase in Braxton Hicks contractions or the loss of their mucus plug, a sign that labour could begin soon.

Weeks 38-40

In the final weeks of pregnancy, the baby’s lungs are fully developed, and their organs are ready for life outside the womb. In the final weeks of pregnancy, the baby continues to gain weight, with the average baby weighing around 2.5 to 3.6 kg by the end of week 40. The mother’s body is fully prepared for childbirth, with the cervix softening and dilating in preparation for labour. Many women experience more frequent contractions and increased pressure in the lower abdomen as they approach their due date. At this point, the baby is considered full term and ready to be born.

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Consult Today

Pregnancy is an incredible journey, and as an expecting parent, it’s natural to have questions and uncertainties. Understanding what to expect at each stage can help you feel more confident and prepared. If concerns arise or you simply want reassurance, consulting with an experienced OB-GYN can provide the clarity you need. Contact Max Hospital to discuss any questions or schedule an appointment. Our team is here to offer the guidance and support you need to navigate your pregnancy with confidence.

Frequently Asked Questions

What are the most critical weeks of foetal development?

The most critical weeks of foetal development are between weeks 3 and 8, during the first trimester. This is when the baby’s major organs and systems begin to form. These early weeks are crucial for the foundational development of the heart, brain, and spinal cord, making them the most sensitive period for foetal development.

How can I tell if I'm having a healthy pregnancy?

Signs of a healthy pregnancy include consistent weight gain, regular foetal movements, a normal heart rate, and the absence of unusual pain or bleeding. Regular prenatal visits are crucial for monitoring your health and the baby’s development. If you experience symptoms like severe headaches, swelling, or vision changes, consult our OB-GYN at Max Hospital for a thorough analysis.

When should I start prenatal classes, and why are they important?

It’s recommended to start prenatal classes around the 20th week of pregnancy. These classes provide essential information about labour, delivery, and postpartum care, helping you prepare mentally and physically. They also offer guidance on breathing techniques, relaxation methods, and what to expect during childbirth.

Can I travel during pregnancy?

In most cases, it’s safe to travel during pregnancy, especially during the second trimester when the risk of complications is lower. However, it’s important to check with your doctor, especially if you have any health concerns. Avoid long periods of sitting, and take breaks to stretch your legs. After 36 weeks, it’s advisable to avoid travel, as labour could begin at any time.

What should I know about prenatal vitamins?

Prenatal vitamins are essential in supporting both the mother’s health and the baby’s development. They contain higher levels of folic acid, iron, and calcium, which help prevent birth defects, support the baby’s growth, and reduce the risk of complications. It’s important to start taking them before pregnancy, if possible, and continue throughout the pregnancy.

What should I expect in the days immediately after childbirth?

After childbirth, you’ll experience physical changes, including bleeding (lochia), cramping, and breast engorgement as your body adjusts. Emotionally, it’s common to feel a mix of joy and exhaustion. Some women may experience "baby blues" due to hormonal changes, which usually resolve within a couple of weeks. Adequate rest, help from loved ones, and self-care are essential during this time.

What are the signs of a pregnancy complication I should look out for?

Look out for symptoms like severe abdominal pain, heavy bleeding, severe headaches, sudden swelling in the hands, feet, or face, and vision changes. These could indicate conditions like preeclampsia or gestational diabetes. If you notice any of these signs, contact your doctor immediately for further assessment.