An IV (intravenous therapy, when fluids, medicine, or nutrients are delivered directly into your veins) is generally used whether you have a vaginal birth or a C-section.
An IV is a source for hydration since you won’t likely be able to eat during labor, especially since labor can sometimes last for more than a day. An IV is also a source of access for life-saving measures, like blood transfusions in the event of significant blood loss and hemorrhaging.
If you have preeclampsia, your care team will administer the antihypertensive medicine and magnesium infusion via IV to help keep your blood pressure down during labor.
Even if you have no existing complications prior to going into labor, the delivery process can sometimes result in unexpected complications, like needing an emergency C-section if you’re in prolonged labor or if the baby’s heart rate drops. Not having an IV only delays the ability to care for you in a safe and quick manner.
Doctors generally discourage refusing an IV, but if you have strong feelings about not having one during labor, you should consult with your delivery provider ahead of time.