There’s multiple facets to this question. For example, a “healthy” pregnancy does not equal a healthy baby.
Obviously there’s the no-brainers: no alcohol, no drugs, no unpasteurized cheese, etc. However, what one dictates as a “healthy” pregnancy may not equate to another’s.
I would say it’s important to establish those prenatal well-visits with your health care provider. Any complications with a pregnancy can be faced directly with your physician. They will suggest diet changes, specific exercises, supplements, etc.
I believe the ultimate goal is to ensure a healthy fetus and, in turn, a healthy child. That will come from paying attention to your body cues and treating yourself with the uttermost respect. Eat healthy (but it’s okay to succumb to those cravings lol), drink lots of water, and if your doctor recommends any prenatal supplements, make sure you take them.
All in all, complications unfortunately happen. The only way you can ensure a healthy pregnancy is by paying attention to the signals your body gives you and seeing a doctor for checkups regularly. If something seems concerning, it’s best to tackle it head on. :)