First of all, let me pray to Allah to give you and your wife patience and strength to endure the trials and challenges that He sends your way, and blesses you to come out of it with enhanced faith. May He inspire you to make the right decision: a decision that would be pleasing to Him.

Now coming directly to your question, let me state: This is an issue the world Muslim council of jurists has discussed in detail; they have concluded after due deliberations that if the fetus has passed hundred and twenty days, abortion is not permissible, unless the continuation of pregnancy will have serious adverse effects on the health of the mother. For details, I am citing here from one of my earlier answers, which summarizes the views of eminent jurists in regard to this issue.

"Abortion or termination of pregnancy is generally considered abominable, and therefore as Haraam since it involves interfering with life-process once it has started. There are, however, differences of opinion about the permissibility of abortion in special circumstances depending on the stage or stages of pregnancy.

1) There is a unanimous consensus among scholars that abortion is considered as absolutely forbidden after twelve weeks of conception (i.e. one hundred and twenty days); this is the point when ensoulment (breathing of soul into the embryo) takes place. To abort pregnancy from this point onwards is akin to committing infanticide, which has been condemned in the Qur'an. Scholars, however, have made a single exception to this rule: If continuation of pregnancy and carrying it through full term proves to be risking mother's life, abortion shall be considered as permissible.
2) Abortion after the expiry of the first forty days of conception is considered as Haraam except in the following exceptional cases: 1) If carrying the pregnancy to the full term exposes the mother to unbearable health problems during or after delivery; 2) if, as determined by the reliable medical practitioners, the child shall be borne with such physical and mental deformity as would deprive him/her a normal life. This decision must be based on the opinion of at least two reliable medical experts in the field.
3) While many scholars consider abortion before expiry of the first forty days of conception as Haraam, a number of them, however, consider it as either permissible or at least not as Haraam.

In conclusion, as Imam Ghazzali has observed, one is discouraged from tampering with the life-process once it has started; the intensity of sin, however, varies according to how advanced the pregnancy is. Thus while it may be considered as less sinful in the very early days, it is considered as absolutely haraam after the ensoulment.

Coming to your specific case, if there is no medical necessity that compels you to seek an abortion, you are best advised to carry it through to full term. Meanwhile, turn earnestly and sincerely to Allah to ease your burden and pain and grant you patience and strength to surrender to His will. Allah has certainly promised to bring relief to all those who turn to Him for assistance. "Whoever remains conscious of Allah, He will grant him/her ease/relief in his affair." (Q.65: 4) The Prophet, peace be upon him, said, "Whoever consistently asks forgiveness of Allah, Allah will appoint for him/her a way out of every conceivable trouble and provide for him/her sustenance in ways he or she can never foresee."