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Fetal development: The 2nd trimester

Week 13: Urine forms

Thirteen weeks into your pregnancy, or 11 weeks after conception, your baby is beginning to make urine and release it into the surrounding amniotic fluid. Your baby also swallows some amniotic fluid.

Bones are beginning to harden in your baby's skeleton, especially in the skull and long bones. Your baby's skin is still thin and transparent, but it will start to thicken soon.