Pregnancy is an incredible journey filled with remarkable changes, both seen and unseen. As your baby develops from a tiny cluster of cells into a fully-formed human being, each week brings about new milestones and fascinating changes. Here's a closer look at the week-by-week development of a foetus:
Weeks 1 to 4: The Beginning
The first few weeks of pregnancy are all about growth at the cellular level. During this time, the fertilised egg, or zygote, travels down the fallopian tube and implants itself into the uterine wall. This marks the beginning of the embryonic stage. By the end of the fourth week, the embryo is about the size of a poppy seed, and the early development of the brain, spinal cord, heart, and other organs begins.
Weeks 5 to 8: The Embryonic Stage
By week 5, the heart begins to beat, and the basic structures for the brain and spinal cord form. By week 8, the embryo is roughly half an inch long, and its arms and legs are developing. The major organs, including the brain and lungs, continue to grow, and facial features like eyes and ears start to become more defined. During this period, the embryo is still very small, but the foundations for all vital systems are being established.
Weeks 9 to 12: Transition to Foetal Stage
By week 9, the embryo is officially referred to as a foetus. The essential organs are formed, and facial features like eyelids and outer ears are beginning to take shape. By the end of week 12, the foetus is about 2 to 3 inches long, roughly the size of a plum. Its bones are hardening, muscles are forming, and the digestive system is beginning to practise movements that will later become functional swallowing and breathing-like actions. At this point, the risk of miscarriage decreases significantly
Weeks 13 to 16: Developmental Milestones
The second trimester begins, and many women find relief from early pregnancy symptoms. During these weeks, the foetus begins to show more defined movements such as sucking its thumb, yawning, or even making facial expressions. The foetus's bones continue to harden, and it starts growing tiny hairs called lanugo. By week 16, the foetus can hear external sounds, and its unique fingerprints have formed
Weeks 17 to 20: Moving and Sensing
By week 17, the foetus' skin is still thin but will soon thicken with the development of fat. Around week 18, the foetus may develop a sleep-wake cycle and start responding to sounds. This is also when many expectant mothers begin to feel their baby's first movements, often described as fluttering or "quickening." By week 20, the foetus is about 9 to 10 inches long, and its brain continues to develop, focusing on the senses such as sight, smell, and touch
Weeks 21 to 24: Building Strength and Preparing for Life Outside the Womb
During these weeks, the foetus’ body continues to grow, and its lungs are developing rapidly, preparing for breathing outside the womb. The foetus starts practising breathing movements, and the lungs produce surfactant, which helps keep the air sacs in the lungs open. The baby also begins to gain weight as fat stores develop under the skin, giving it a more defined shape. By week 24, the foetus is about 12 inches long and weighs around 1.5 to 2 pounds. This is also the point where the foetus reaches viability, meaning it could potentially survive outside the womb with intensive medical care if born prematurely
Weeks 25 to 28: Refining Senses and Movements
By the seventh month, the foetus' eyes are fully formed, and it can blink. It continues to practise breathing, and its movements become more coordinated. The nervous system is maturing, allowing the foetus to respond more effectively to stimuli, including sounds, light, and touch. The baby may start to move more frequently and change positions often, preparing for birth
Conclusion
Each week of foetal development is marked by incredible growth and transformation. From the earliest stages of cellular division to the complex preparation for life outside the womb, the journey from conception to birth is filled with wonder and amazement. Understanding these developmental milestones not only fosters a deeper connection with the growing baby but also helps in preparing for the changes that lie ahead.
References:
- https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth
- https://www.healthline.com/health/pregnancy/pregnancy-symptoms-week-8
- https://www.healthline.com/health/pregnancy/miscarriage-rates-by-week
- https://www.ncbi.nlm.nih.gov/books/NBK526092/
- https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/first-fetal-movement/
- https://www.whattoexpect.com/first-year/preemies/fetal-viability
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4460088/