Complex sentence: Isotretinoin is known to cause birth defects due to in utero exposure because of the molecule's close resemblance to retinoic acid, a natural vitamin A derivative which controls normal embryonic development.
Split into simpler sentences: Isotretinoin is known to cause birth defects due to in utero exposure. This is because of the molecule's close resemblance to retinoic acid, a natural vitamin A derivative which controls normal embryonic development.