Although, I am not an authority on this as I am not a medical of science researcher. But given the role of United Nations and its agencies in the world and shaping the beautiful world that we have today, I would find UN resources really helpful.
Here is a link to World Health Organization, the WHO and related pages do not come up frequently in google searches as the WHO is non-commercial organization with only motive of improving global health and living standards - albeit not making economic gains.
Searching about anything on WHO is very simple, you have to just type in information you are looking for in the search-bar at the website and it would take you to the relevant papers and information (the database is also bilingual, i.e. papers in all official United Nations languages are normally there, this includes, German, French, Spanish, Dutch, English to name few)
The website is a great source of authoritative information for expectant mothers and language used is very simple (atleast I can understand it, despite of not being a doctor) - it gives a lot of information, which might be useful to discuss with your mid-wives or be generally aware of.
Stay health all