Determining who is halachically considered the mother of a child conceived through egg donation is a matter of debate. If the birth mother is the halachic mother, then the child would not require conversion. But if the egg donor is the halachic mother, then the child would need a conversion. It is not certain if this could be accomplished through immersion during pregnancy.
In practice, babies born from procedures involving non-Jewish surrogates or egg donors often undergo conversion in early infancy to ensure that they are considered Jewish according to all opinions.
If this is an actual practical situation, then we recommend arranging a personal consultation with a Nishmat Fertility Counselor, a Yoetzet Halacha who has completed additional specialized training in this area. Consultations are free and can take place in person, by phone, or via internet conference.
This response was updated on 13 April, 2021.