For starters, I would focus on Indian recipes. Curated list of traditional Indian recipes to cater to the nutritional, and emotional needs of the mother. Traditional Indian cooking has a host of such proven recipes. Mapping them to modern day nutritional and allergen information, would be a logical next step.
Allied to this would be effective and proven home remedies for common concerns like morning sickness, cough, cold, constipation etc. While several allopathic remedies exist, I believe that it is critical to be drug free during this important time and hence would tend towards natural or even ayurvedic solutions. This however is a personal opinion.
Beyond the physical, it is critical to cater to the emotional and mental well being of the expectant mother. Meditation, yoga and other such aspects, mapped to the specific trimesters , would be the next component I would include. Again, I would not limit this to mere asanas, but would try to compile or curate a holistic well being regimen.
I'm still debating the need to include cultural aspects. In all parts of India, various traditions exist for the celebration and well being of the expectant mother. Unfortunately we have list out on the scientific basis for many of these traditions and merely follow them from a superstitious/religious angle today. If those with more knowledge about this could chip in, I may want to include some of these aspects.
Finally, a directory of service providers (medical and otherwise) relevant to the care and aid of pregnant women.
Apart from this existing apps cover pretty much everything else in a comprehensive manner.