Why do I have a brown line down my tummy?

This is called the linea nigra. The linea nigra is dark vertical brown line down the middle of the abdomen. It is common and due to the hormone changes of pregnancy.

There can also be associated increased pigmentation of the breast areola (area around the nipples), of  the nipples and occasionally on the face (called cloasma).

These pigmentation changes can also happen while taking the oral contraceptive pill.

What can be done?

Nothing. Be reassured the increased pigmentation usually resolves after pregnancy, though this may not be until after you cease breastfeeding.

Such pigmentation can sometimes occur when woman takes the combined oral contraceptive pill and occasionally even with hormone replacement therapy and will disappear usually if such hormone treatments are ceased.