The answer may come as a surprise to you. It did to me during my first pregnancy. Many obstetricians/gynecologists will tell you far little about healthy eating habits, calories, and minerals and vitamins than you will have expected. During your first prenatal appointment, your OB or a nurse may ask you questions about your nutrition, and you will probably also be weighed. Your OBGYN is extremely likely to bring up the importance of prenatal supplements containing vitamins and minerals, and especially the B vitamin folic acid which has been scientifically proven to prevent birth defects.
Once that's off their list, your healthcare provider may take care to look at your pregnancy weight gain, but may not talk about nutrition much at all. Make sure to discuss any specific concerns you have about nutrition, especially if you have food allergies, are a diabetic, or a vegetarian do not wait for your OBGYN to bring this issue up themselves. If you have unusual concerns or just want more information, it is good to remember that an OBGYN specializes in gynecology, prenatal care, and labor and delivery. That means that you may want to see a nutritionist for specific questions about eating habits.
A nutritionist, particularly one that specializes in pregnant women, is far more likely to help you adequately address any specific worries or questions you may have. If you are totally healthy and have no concerns, eating well and taking care to consume foods from all major food groups is the best approach. Eating well does you a much better service than regularly taking prenatal supplements. Also read: What vitamins do you need during pregnancy?