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Your Second Month of Pregnancy Has Begun!
By Week 5 of pregnancy, your baby is made up of three distinct cell layers, each of which develops into different organs and body systems.
The outer layer (ectoderm) forms the brain, nervous system, skin, hair, nails, the lenses of the eyes, inner ear tissues, nose and sinuses, tongue, mouth, anus, tooth enamel, pituitary gland, and mammary glands.
The middle layer (mesoderm) develops into the bones, muscles, blood vessels, heart, and reproductive organs.
The inner layer (endoderm) forms the stomach, liver, intestines, lungs, and urinary system.
At this stage, the eyes and facial features begin to develop. The heart also starts to form, and approximately 25 days after conception, it begins to beat, although the heartbeat is not yet detectable.
During the fifth week, your baby's reproductive system also begins to develop. Depending on the baby's sex, the ovaries (in girls) or the testes (in boys) start to form.
Your baby now measures approximately 7–8 mm in length and weighs about 0.01 g—roughly the weight of your lower eyelid.
