Congratulations on your pregnancy. You're in the 75% of women that will experience the linea nigra during pregnancy. A natural pregnancy phenomenon is nothing to worry about, but rather should be embraced. It’s just a sign that your pregnancy hormones are kicked in gear. For most women, the linea nigra starts to be noticeable at the end of the first trimester (from about 12 weeks) but If you're a first-time mum, you could begin developing a baby bump any time between 12 and 16 weeks hence linea nigra
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