English term (edited): with more uncounted stillborn or miscarried pregnancies

I would recommended splitting this into two sentences in order to facilitate readability and maintain coherence.

What the text appears to mean is that, in addition to living children affected by whatever is being referred to (a medication, toxic agent, etc. - you have not supplied this vital information in your posting), there were cases of stillbirths and miscarriages resulting from exposure to/use of the medication, agent, etc.

“Un número adicional” makes it sound like perhaps “only a few” additinal cases resulting in stillbirths or miscarriages were involved, and this does not appear to be the intended meaning of the original (which, while vague, suggests that perhaps the number of involuntarily terminated pregnancies was not small).

--------------------------------------------------
Note added at 1 hr (2018-06-29 18:06:04 GMT)
--------------------------------------------------

Typo:
“additional”