I was cast upon thee from the womb: thou art my God from my mother's belly.
From the womb. The reference is to the parent receiving the child at birth (Genesis 30:3). 'I fell as it were into thy lap, stretched out to receive at my birth, when otherwise I should have died' (Hengstenberg).
Thou art my God - i:e., thou hast shown thyself to be "my God," by acts of love, from my conception and birth. God was His God "from the mother's belly;" God was His Father from everlasting. The "my God" at the close of the first part returns to the very point with which He opened in Psalms 22:1.