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

Dear Brothers & Sisters,
As-Salaamu-Alaikum wa Rahmatullahi wa Barakatuh. (May Allah's Peace, Mercy and Blessings be upon all of you)
One of our brothers/sisters has asked this 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.
(There may be some grammatical and spelling errors in the above statement. The forum does not change anything from questions, comments and statements received from our readers for circulation in confidentiality.)
Check below answers in case you are looking for other related questions:
If he gives his second wife the cost of tuition fees, is he obliged to give the same amount to his first wife?
The first wife’s approval is not a condition for marrying a second wife

Answer:
Praise be to Allaah.

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.

Whatever written of Truth and benefit is only due to Allah's Assistance and Guidance, and whatever of error is of me. Allah Alone Knows Best and He is the Only Source of Strength.
Your brother and well wisher in Islam

Related Answers:
How can he treat his two wives fairly?
He has two wives and he does not allow one of them go out or to receive visits from her family except with his permission
The reason why plural marriage is permitted for men but not for women
If he gives his second wife the cost of tuition fees, is he obliged to give the same amount to his first wife?
The first wife’s approval is not a condition for marrying a second wife

Recommended answers for you:
Rings and chains for men
Black Magic and Satanic Possession
A list of brief Islamic sayings for sending to one’s friends
Fasting is not accepted if one doesn’t pray
Praying at graves and the conditions of intercession