I’m not sure that there are “best” foods. Following a healthy diet that consists of lean proteins, fruits, veggies, whole grains, dairy and low in processed foods and added sugars is key for optimal health.
During the first trimester a mother can often suffer from morning sickness, so eating frequent meals and finding foods that help to settle a disagreeable tummy is key. Those foods will be different for each woman and different for each pregnancy, as I found out. For most women, morning sickness will subside by the end of the first trimester. Thankfully!
A doctor should prescribe a pre-natal that should also be taken throughout pregnancy and even while a woman is thinking about getting pregnant. You can also discuss your diet with your physician if there are areas you’re concerned about or if your morning sickness is severe, there are supplements and medications your doctor can prescribe to help you lessen those symptoms.
I hope that helped provide some light on the area.