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.
There is no harm if a woman gives up her right of maintenance and right of equal share in overnight stay of her husband provided the husband accepts it. It is reported in Saheeh al-Bukhaari and Muslim that ‘Aa’ishah said: “Sawdah Bint Zam'a gave up her turn to me, and so, the Prophet used to give me both my day and the day of Sawdah .”
Also, these are one's rights and it is permissible for one to give up his rights. The approval of the husband is made a condition since he has the right of enjoying his wife.
If the husband agrees to delay pregnancy then he has to abide by this condition since the Prophet said: “From among all the conditions which you have to fulfill, the conditions which make it lawful for you to have sexual relations (i.e. the marriage contract) have the greatest right to be fulfilled.” [Al-Bukhari and Muslim]
Know that delaying pregnancy should be through the legal ways such as using condoms, etc.
Allah knows best.