From a completely biological standpoint, nature "knows" when populations of flora or fauna are getting out of control and enacts measures to attempt to control that population, so I can buy that their body is telling them that they "shouldn't" have a baby. That said...
...it's my personal opinion that I would much rather see a child born to a parent or parents who wanted that child so much that they were willing to put that amount of dedication and effort into bringing them into the world, than to see another unwanted product of "natural" teen pregnancy shipped through the system. Of course, spending a fortune and months or years to have a baby is no guarantee that the child is loved and cared for properly just as not all teen pregnancies end in a child that is unloved and uncared for, but when weighing the odds...
I have a
much bigger problem with people who have severe, known diseases/deformities that are known to be inheritable (for example, Neurofibromatosis, Cystic Fibrosis, or Schizophrenia just to name a few) having children, but that's another can of worms.