There is nothing wrong with you. It’s common for a vertical line during pregnancy, which seems to divide the bump, to appear. That line was there well before you got pregnant. Still, with elevated levels of pigmentation triggered by hormonal changes, the line becomes more brown-ish – and therefore, visible – as soon as the second trimester of pregnancy begins. It’s called the linea nigra, which is very common, while not all pregnant women have it.
The linea nigra can measure up to 1 cm wide and stretch from the lower abdomen up to the belly button. It draws attention for obvious reasons: it’s positioned right on the abdominal musculature that distends to accommodate the baby. The more the bump grows, the more evident the line becomes.
After birth, the line disappears in a couple of weeks. Until then, if you’re headed to the beach or the pool, don’t forget the sunscreen to avoid getting new spots on your skin.