Trying to get pregnant? Make sure you know the bottom line on baby-making—what you don't understand can affect your bub-to-be's health.
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Despite how foreign they can look on your body, stretch marks (or striae) are a normal part of pregnancy: Half of all moms-to-be can expect to find these rippled stripes on their skin.
What's the cause?
"Stretch marks are an odd entity," says dermatologist Alan Rosenbach, M.D., a clinical assistant professor at Keck School of Medicine, University of Southern California in Los Angeles. "Considering how common they are, we don't know much about their cause, though some suspect the reasons are at least partly hormonal."