As my midwife explained to me, the baby is so well-protected, it would take the force of a severe car wreck to injure the baby. The presence of relaxin in the mother, however, loosens the joints and leaves the mother more prone to orthopedic injury. Gauge your level of comfort. How likely are you to fall on a road bike. Of course, if you're going to be a nervous wreck out on the road, a trainer is your best bet.