Human Development Before Birth: The Three Trimesters

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• Biology
• Secondary Education

Human Development Before Birth: The Three Trimesters

What do you already know about the stages of human development before birth?

Learning Objective

At the end of the lesson, you will be able to summarise the key developments that occur in each trimester of human development before birth.

Starter Activity

Discuss with a partner: What do you already know about how a baby grows before birth? Share one interesting fact with the class.

Introduction to Human Development Before Birth

Human development before birth happens in three distinct stages, or trimesters. Each trimester features unique and remarkable changes in the developing baby.

First Trimester: The Foundations

Key Developments

All tissues, organs, and organ systems begin developing. By 8 weeks, the embryo is called a foetus. Begins to move arms, fingers, and toes. Fingerprints appear.

Risks and Challenges

The embryo is very vulnerable to environmental influences (e.g. pollution). Poor nutrition, such as lack of folic acid, may lead to birth defects affecting the brain and spine.

Second Trimester: Growth and Development

This period is marked by significant growth. The foetal heartbeat can be heard. Hair grows, eyes open, and the foetus can suck its thumb or get hiccups.

Second Trimester: Challenges

Immune System

The foetus does not have a developed immune system, making infections risky.

A premature baby at this stage struggles to survive. Lacks ability to keep constant body temperature and is at risk for respiratory failure.

Survival Outside the Womb

Third Trimester: Rapid Growth

This is a period of very quick growth. The foetus responds to music and familiar voices. Fat builds up under the skin to provide warmth after birth.

Third Trimester: Brain Development

The brain develops rapidly during this trimester. Around 250,000 brain cells are formed each minute. Protein is vital for this process.

Getting Ready for Birth

Brain Growth

Foetus moves into a head-down position, ready for delivery. Organs and systems mature to function outside the womb.

Activity: Timeline Match-Up

Mind map on Canva

Plenary: Quick Quiz

1. At which stage are all organs developing? 2. When can a heartbeat be heard? 3. When does the baby gain fat for warmth? Answer these questions to recap the lesson.

Write down 3 things you learned in this lesson.

Write down 2 things you want to know more about.

Ask 1 question about something you haven't quite understood yet.