Stritzel H, et al. - Researchers investigate the hypothesis that the rates and odds of twinning increase with parity among teenage and young adult mothers who do not use assisted reproductive technologies (ART). A retrospective, population-based cohort study was conducted using 2009–2018 United States National Vital Statistics data on 11,383,370 (58.94% first, 41.06% repeat) births to women ages 15-24 years. The findings revealed that repeat young mothers, especially teenage mothers, are a high-risk group in terms of infant and maternal health outcomes; their higher rate of twinning puts them at additional risk for adverse birth outcomes. It has been considered that practitioners may counsel young mothers at risk of subsequent unintended pregnancy on elevated risk of twinning.