Prenatal care and healthcare providers
Whether you choose a gynecologist/obstetrician for your prenatal care, or opt to receive care from a midwife, your healthcare provider will keep a close watch on your health and your developing baby. Through routine checks that normally include measuring blood pressure, doing urine and blood tests, keeping track of your weight, you know whether you are healthy and whether all is fine with your health or if any special care is needed. And with ultrasounds, listening to the fetal heartbeat, checking the baby's weight and possibly doing prenatal screening or diagnostic tests, healthcare providers keep an eye on your baby and his or her development in the womb.
What you can do
Of course, while prenatal care gives you important information, the things you do in between those appointments have the largest impact on your health. Eating healthily and exercising regularly are the best things you can do for yourself and your baby. It is best if pregnant women make sure they have as little stress as possible (though life can mess with that goal!). Listen to your body and prevent overdoing things if you can. It is perhaps best to attempt to gain your relevant vitamins and minerals through nutrition alone, but if for whatever reason you have concluded that you won't be able to do so, taking a good multivitamin and mineral supplement is fine too. You can ask your doctor or midwife to recommend a good one. You can also consider taking omega 3 fatty acids, something that has been shown to be extremely beneficial in recent years.