Marrying a Pregnant Woman from Zina
3-4-2001 | IslamWeb
Question:
I want to marry a pregnant Muslim girl. A girl who had relation with another boy and they got physically involved and now he (boy) is refusing her and avoiding her completely. And the girl is beautiful and good mannered & I like her and she likes me. Please reply in the light of Qur'an And Sunnah.
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
In principle, marrying an adulteress or fornicator is prohibited in the Sharee’ah. Allah Says (what means): {The fornicator does not marry except a [female] fornicator or polytheist, and none marries her except a fornicator or a polytheist, and that has been made unlawful to the believers.} [Quran 24:3]
'Amr ibn Shu'ayb narrated from his father, from his grandfather, who said: "There was a man named Marthad ibn Abu Marthad, and he was a man who would carry captives from Makkah to Al-Madeenah." He said: "And there was a prostitute woman in Makkah called 'Anaaq, who was a friend of his [...] I went to the Prophet and I said "O Prophet of Allah! May I marry 'Anaaq? He kept silent. Then the following verse was revealed: “The fornicator does not marry except a [female] fornicator or polytheist, and none marries her except a fornicator or a polytheist, and that has been made unlawful to the believers.} [Quran 24:3] He called me and recited this (verse) to me, and said: Do not marry her." [Abu Daawood, at-Tirmithi and an-Nasaa’i]
But if she makes a sincere repentance then marrying such a woman is permissible since repentance invalidates all the previous sins.
However, if she is pregnant then marrying her is not permissible till she gives birth; after that one can marry her. If she is not pregnant one can marry her after having passed one monthly period to make sure that she is not pregnant. This is because semen in the condition of marriage has its special rules and sanctity, so semen of marriage should not be mixed with the semen of illicit relations.
For more benefit, please refer to Fataawa 213442, and 122443.
Allah knows best.