All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
If one did not specify a certain time for fulfilling the vow and he cannot immediately execute it due to some reasons, it is permissible to delay it until fulfilling it becomes possible. Consequently, you should delay the fast of these two days until you give birth. You are not required to give money. If you will never be able to fulfill it, then you are required to offer expiation like for a broken oath. It was narrated that the Prophet said: "The expiation for (breaching) a vow is the same as the expiation for (breaking) an oath." [Muslim]
It was also narrated through a Mawqoof and Marfoo‘ Hadeeth on the authority of Ibn ‘Abbaas that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever made a vow that is beyond his ability, its expiation is the same as that of an oath." [Abu Daawood and Al-Bayhaqi. The Marfoo‘ narration is ranked as weak by Al-Albani]
In Al-Mughni, Ibn Qudaamah said:
"If one is unable to fulfill a vow due to a temporary reason, such as sickness or similar reasons, then he should wait until the reason disappears, and no expiation is due in this case. This is so because the time of fulfillment has not yet expired. This is similar to the case in which one gets sick during Ramadan. But if he is unable to fulfill the vow due to a permanent reason, then the expiation becomes due."
We ask Allaah to help you to be constantly obedient and to Grant you a good end of life. If Allaah decrees death for you, it is recommended that someone of your close relatives fast the two days on your behalf.
In Al-Mughni, Ibn Qudaamah said: "Whoever vowed to fast and then died (before its fulfillment), a close relative of his should fast on his behalf."
This opinion is supported by the following Ahadeeth:
• It was narrated on the authority of Ibn ‘Abbaas that he said:
"A woman came to the Prophet and said, "My mother died, and she had vowed to fast but she did not do so. Shall I fast on her behalf?" He, sallallaahu ‘alayhi wa sallam, said, "If your mother had died in debt and you paid it off on her behalf, would that not clear her of liability?" She replied in the affirmative. He then said, "Then fast on behalf of your mother." [Al-Bukhari and Muslim]
• It was also narrated on the authority of Ibn ‘Abbaas that Sa‘d ibn ‘Ubadah consulted the Prophet regarding a vow that his mother made; she died before fulfilling it, and he (the Prophet, sallallaahu ‘alayhi wa sallam) ordered him to fast on her behalf. This action became a Sunnah (a followed practice) from that time onwards. [Al-Bukhari]
• It was narrated on the authority of ‘Aa‘ishah that the Prophet said: "Whoever died and he ought to have fasted, then his relative (who is entitled to inherit him) must fast on his behalf." [Al-Bukhari and Muslim]
Allaah Knows best.