Answer:
   
   Technically, no.
   
   It is not a bris that makes a child Jewish, it is the circumstances of
   birth. In traditional Judaism, if the child is born of a Jewish
   mother, the child is nominally Jewish. For religious reasons, both
   Conservative and Orthodox Jews view it as a terrible mistake to avoid
   giving your Jewish child a brit milah (hebrew) (Note that a medical
   circumcision does not count in halakha (Jewish law) as a brit).
   Nonetheless, a Jew is a Jew, and he can join a synagogue and
   participate just as fully as any other Jew.
   
   Note that adults can choose to have a circumcision later in life
   (although medical involvement is necessary, along with religious
   involvement). Should a medical circumcision take place, your son could
   always get the full religious benefit of a second circumcision: the
   procedure is called hatafat dam brit, "the drawing of a tiny drop of
   blood in the name of the covenant". This action and ceremony can be
   done by a mohel (Hebrew)/moyel (Yiddish) nearly painlessly (surprise!)
   either when your child is still an infant, a child or even as an
   adult.
   
   Lastly, note that in Reform Judaism, under the Patrilineal Descent
   decision, either parent being Jewish gives the presumption of the
   child being Jewish. However, Reform Judaism requires that this
   presumption be confirmed by the child being raised with appropriate
   Jewish lifecycle and yearcycle events (i.e., observing holidays, home
   pratices, religious education)... and one of the specifically
   recommended events is a circumcision!