4 Month old stopped cooing

My four month old daughter recently stopped cooing.  Previously, she made many sounds and often "talked" in a back and forth fashion (making sounds when we stopped talking to her).  However, she abruptly stopped making sounds.  Overall, she has been very quiet lately.  

She continues to have good eye contact and is smiling.  She sometimes turns towards our voice (although not consistently) and seems to respond to sounds.  However, even with repeated efforts to encourage cooing, she is not making sounds.  Should I be concerned?  Could this be a sign of hearing loss?  I should also report that her hearing was screened at birth and  was fine.  Thank you for your assistance.

[Kevin Kennedy, Ph.D.]

The behavior change is unusual for her age. Generally, children of that age very much like to make sounds, moreso if you are looking at them but at other times as well. Have you called this to the attention of the pediatrician? If so, what guidance did you receive? If not, please do so.