In "Empire of the Summer Moon", S.C. Gwynne mentions that the Comanches had very low birth rates, due at least in part to a trend of horseback riding-induced miscarriages. Modern medicine does identify riding as a risk to the pregnancy... but how great was this risk for people like the Comanches, who could travel long distances on horseback almost daily, sometimes for weeks or even months? Do we have any knowledge of this same issue in other populations with similar reliance on the horse (such as other Plains tribes, or even Central Asian nomads like the Mongols or Turkic peoples)? Were there any cultures who had ways to mitigate this risk, or was it just accepted that some pregnancies would be lost?