Baby Size
Week 5

Your Baby is the Size of a Sesame Seed

Week 5

Sesame Seed

Length

0.2 cm / 0.1 in

Weight

< 1 g

Your baby's heart begins to beat this week as the neural tube — the foundation of the brain and spinal cord — starts to form.

Development at Week 5

At 5 weeks, three distinct layers of cells are forming that will become all of your baby's organs and body structures. The primitive heart is beginning to beat, even though it is not yet fully formed. The neural tube, which will develop into the brain, spinal cord, and nerves, is also starting to close.

Next week

At week 6, your baby will be the size of a Lentil.
See Week 6

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