In the name of Allah the Greatest
The second Nikah is invalid. The two are not and never were husband and wife, because the girl is already married to someone else. It is forbidden for them to be together! (Al-Hidayaa)
However, It is not deemed as Zina (Fornication, Adultery) for the groom because he was unaware the girl who he married was already married. Because of his lack of knowledge of this fact it does not constitute as Zina (Shami Vol.2 Pg 380). For the girl it is Zina because she knew what she was doing, that is she was marrying while being in wedlock with another.
You say that the girl in question is expecting from her second marriage. Before one is able to answer the reminder of your enquiry can you please reply to the following questions.
? How long has she being in this invalid second marriage?
? Why do you assume it is the child of the deceived and mislead second groom?
We look forward to your reply
And Allah knows best
26th September 2005
Shami Vol.2 Pg 380
Badaeus Sanae?e Vol.2 Pg 550