Critical Reasoning

Having some trouble comprehending the stimulus.
Question about answer choice B

Premise (These records also indicate that mothers who had received adequate prenatal care were less likely to have low birth weight babies than were mothers who had received inadequate prenatal care)addresses the relationship between mothers who receive prenatal care and the babies birth weight.

By selecting answer choice B, is the argument that now there are or could be more mothers giving birth to premature babies and therefore risk a low birth weight?

I still don't see how this answer attacks the causal relationship between Adequate prenatal care and low birth weight.

Thanks in advance!!