What Is Happening to Your Baby This Week?

How does your baby develop throughout pregnancy, from a tiny embryo to a full-term newborn?

18/08/2026

What Is Happening to Your Baby This Week?

Weeks 1–4: A New Life Begins

At conception, a single fertilised egg (zygote) begins to divide rapidly as it travels from the fallopian tube to the uterus. By day 6–10, the cluster of cells (now called a blastocyst) implants into the lining of the uterus. This implantation triggers the hormonal changes — including rising hCG levels — that cause a pregnancy test to show positive.

By the end of week 4, the foundation of the neural tube (which will become the brain and spinal cord) has begun to form. This is why folic acid supplementation is so critical from the very beginning — neural tube defects form in weeks 3–4, often before most women even know they are pregnant.

Weeks 5–8: Organs Begin to Form

Between weeks 5 and 8, your baby is called an embryo and is developing at an extraordinary pace. The heart begins to beat by week 6 and can be detected on an early ultrasound. By week 8, all the major organ systems — brain, heart, lungs, kidneys, liver, and limbs — have begun forming, though they are still very immature.

Your baby at 8 weeks is approximately 1.6 cm long — about the size of a grape — and has distinct facial features beginning to emerge, including early eye structures and a forming mouth and nose. Arms and legs, once paddle-shaped buds, are developing recognisable fingers and toes.

Weeks 9–13: From Embryo to Fetus

From week 9 onwards, your baby is called a fetus. Fingers and toes separate, the external genitalia begin to differentiate, and your baby begins to make small spontaneous movements — though you will not feel these yet. The kidneys begin producing urine. The intestines, which were temporarily located in the umbilical cord, migrate back into the abdomen.

By the end of the first trimester (week 13), your baby is fully formed in miniature — approximately 7–8 cm long and weighing about 23 grams. The risk of miscarriage drops significantly after week 12, as the most critical phase of organ formation is complete.

Weeks 14–26: Growth, Senses, and Movement

During the second trimester, your baby undergoes dramatic growth and sensory development. By weeks 18–20, most mothers feel their baby's movements for the first time — gentle fluttering sensations that become stronger and more frequent over time. By week 22, your baby can hear sounds including your heartbeat, your voice, and sounds from outside the womb.

By week 24, your baby has a realistic chance of survival if born very prematurely, due to continuing lung maturation. By week 26, the baby weighs approximately 900 grams and its eyes begin to open. This is a critical period for brain development — severe malnutrition or infection during this time can affect your baby's cognitive development.

Weeks 27–40: Preparing for Birth

In the third trimester, your baby's primary task is growth and final organ maturation. Fat stores accumulate, providing insulation and energy reserves for birth and breastfeeding. By week 32, the lungs are approaching maturity, though they continue developing until birth. By week 36, most babies settle into a head-down (cephalic) position in preparation for delivery.

Your baby's brain grows rapidly throughout the third trimester, nearly doubling in size. From week 28, you should feel clear, regular movements every day. A significant reduction in movement is a warning sign — go to your nearest hospital or health facility the same day. By week 40, your baby weighs on average 3.3–3.5 kg and measures approximately 50 cm.

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