An Embryo Forms: Weeks 4 to 8 of Pregnancy | Parents

Summary

In the early weeks of pregnancy, a tiny ball of cells develops rapidly into an embryo. By the fourth week, cells differentiate into layers that form the brain, heart, bones, and organs. As the baby grows, it progresses from the size of a poppy seed to a blueberry by week eight. Major developments include the formation of the neural tube, heart, and limbs, as well as the baby's first blood cells. Around week six, genetic factors from the father determine the baby’s sex. The script describes key stages of early fetal development, including rapid growth and organ formation.

Takeaways

• 🌱 The baby, at four weeks, is the size of a poppy seed, and the cells separate into three layers that will form organs and skin.
• 🧠 The outermost layer develops the brain, nervous system, and skin, while the middle layer forms the heart, bones, muscles, and reproductive system.
• 🫁 The innermost layer will develop the stomach, intestines, lungs, and other organs.
• 🩸 Blood cells are being produced in the yolk sac, with major changes expected by week five, when the baby is the size of a peppercorn.
• 👶 The neural tube, which will become the brain and spinal cord, starts closing, and the heart begins beating around 22 days after conception.
• 🤰 Signs of pregnancy, like nausea and fatigue, may begin during the fifth week.
• 💧 By week six, the baby is the size of a lentil and is protected by amniotic fluid, with facial features forming and the heart pumping fetal blood.
• 🧬 The baby's sex is determined by the sperm, and if a Y chromosome is delivered, the embryo will develop into a boy.
• 👂 By week seven, the baby is the size of a coffee bean, and features like mouth, nostrils, and ears are becoming visible.
• 🦶 By week eight, the baby is the size of a blueberry, with webbed fingers and toes that will soon separate into individual digits.

Q & A

What is the size of the developing baby in the fourth week of pregnancy?

In the fourth week, the developing baby is about the size of a poppy seed.

At what stage do the cells of the baby begin to form three distinct layers?

The cells begin to separate into three distinct layers in the fourth week of pregnancy.

What does the outermost layer of cells develop into?

The outermost layer forms the brain, nervous system, and skin.

What internal structures does the middle layer of cells form?

The middle layer forms the heart, blood vessels, bones, muscles, and reproductive system.

When does the baby's heart start beating, and how does it form?

The baby's heart starts beating around 22 days after conception, forming from an S-shaped loop.

What size is the baby by the fifth week, and what changes occur during this time?

By the fifth week, the baby is about the size of a peppercorn. The brain, spinal cord, heart, and blood vessels are well underway, and the neural tube starts closing.

How does the gender of the baby get determined?

The baby’s gender is determined by the sperm, which can carry either an X or Y chromosome. If the sperm carries an X chromosome, the baby will be a girl, and if it carries a Y, the baby will be a boy.

What is happening with the baby's limbs in the sixth and seventh weeks?

By the sixth week, little knobs of tissue have formed that will become the baby's arms and legs. By the seventh week, the arm buds look like paddles.

What major developments occur with the brain by the seventh week?

By the seventh week, the brain is growing rapidly, and the right and left sides of the brain become more defined, with the right side handling nonverbal and spatial tasks and the left side handling speaking and writing.

What significant change happens to the baby's fingers and toes by the eighth week?

By the eighth week, the hands and feet have webbed fingers and toes, and the extra tissue between them will soon be reabsorbed to reveal individual fingers and toes.