His wife is pregnant and he wants to marry a second wife; should he delay the marriage contract?
Question

                I am married and have a wonderful family. I was contacted by a sister whom I was intended to marry prior to this current situation. The question of polygamy was raised and thru futher conversation began plans to expand my family. We have coorespond for sometime by way of the internet and phone. Sometime as pasted an due to the fact that my current wife is pregnant. I delayed any chance of actually marring. I want to write a marriage contract in order to not sin. What would you advise? She wishes to marry and not wait. I pray that I am asking my question in the best manner. Can we write the contract and delay consumating after the arrival of the child. Or should I wait and repent to Allah.
Praise be to Allah.
    It is permissible for a man to marry a second wife and as 
    many as four wives, because Allaah says (interpretation of the meaning): 

    “then marry (other) women of your choice, two or three, or 
    four; but if you fear that you shall not be able to deal justly (with them), 
    then only one”

    [al-Nisa 4:3]

    This is subject to the condition that he be financially and 
    physically able for it, and able to treat them fairly. 

    Secondly: 

    You can do the marriage contract now, and delay consummation 
    until your first wife gives birth, or you can do the marriage contract and 
    consummate the marriage straight away, because there is no connection 
    between your wife’s pregnancy and your taking a second wife. 

    Undoubtedly in a case such as yours it is better to do the 
    marriage contract so that you will not do anything haraam. By doing the 
    marriage contract, the woman will become your wife and it will be 
    permissible for you to talk to her, be alone with her and touch her, and 
    everything that it is permissible for a man to do with his wife. 

    But you have to fear Allaah and treat your wives fairly, and 
    it is not permissible for you to favour one of them at the expense of the 
    other. 

    And it is not permissible for you to form a relationship with 
    a non-mahram woman. If any such thing has happened then what you must do is 
    repent to Allaah and put an end to this relationship until the marriage 
    contract is done. 

    And Allaah knows best.