Does the baby start to grow about an inch under belly button?

No. It is a common misconception that the belly button is the starting point for measuring the growth of a baby in the womb. The baby's growth is usually measured from the top of the head to the bottom of the spine, known as the crown-to-rump length (CRL). This is because the baby's legs are usually bent up during the early stages of pregnancy, making the CRL a more accurate measurement of growth during the first trimester. Once the baby reaches about 12 weeks of gestation, the legs start to straighten out, and the CRL is replaced by the measurement from the top of the head to the heel, which is known as the crown-heel length.