Reference: Silsilah Kitaab ad-Da’wah (12), al-Fataawa – Volume 3, Page 126-127
Question: There is a woman who has been unable to conceive; the doctors carried out some tests and discovered the eggs [in the womb] are dead. So they carried out an operation to implant [more] eggs, and now she is pregnant with four [babies]. When the doctors discovered this, they informed her husband. He said that he does not want four, because his wife may become tired and overcome [by the pressure]. So he said remove two and leave [the other] two. The doctors said they will not do that without a fatwa from the noble Shaykh Muhammad ibn Saalih al-‘Uthaymeen; Keeping in mind that the duration of the pregnancy is three months, is it permissible for the doctors to carry out this operation, since they have put on hold [the operation] until they receive your verdict? [And] may Allaah reward you with good.
Response: Regarding the implanting of the eggs, we shall not discuss it because this [stage] has now passed. As for removing some of that which she is carrying in her womb, and whilst she has apprehensions [in proceeding with all four], then so long as the pregnancy has not passed four months there is no harm in this. However, if the period of four months has passed, then it is not permissible to abort under any circumstances.