Hey there, I am a nurse at a birth center. We only require a saline lock if the mom has a pretty strong history of post partum hemorrhage, if the mom is group b strep positive and wants antibiotics, or if the mom's hemoglobin levels are below 11.0 or so. Moms don't usually disagree with this, because it is discussed extensively during prenatals; it isn't something that is sprung upon them during labor. Alternatives are discussed as well (retesting for GBS, means of raising iron levels, etc).
I don't think that anyone actually does heparin locks any more. They are often still *called* heparin locks, but they actually don't use heparin in peripheral locks anymore, just saline.
Many people choose a saline lock in stead of a continually running IV so they don'e have to mess with the tubing and the IV pole, etc. BUT, if you aren't going to have fluids running, you need to make sure that you are able to drink fluids to keep yourself hydrated. Incidentally, if they say you "aren't allowed" simply be noncompliant. They can't physically wrestle the fluids from your grasp!
In defense of inserting a saline lock during labor.......if someone hemorrages drastically after birth, their vessels are constricted and it is very difficult to insert an IV. Time is of the essence, and if it takes several attempts, that can make the difference between life and death, literally. And while no one wants to be treated like a medical problem, if someone has a history of hemorrhaging after their first three births, doesn't it seem prudent to hope for the best (no hemorrhage) but be prepared for the worst? Healthy women with good nutrition don't usually need an IV or even a saline lock unless something goes awry during labor (like, they vomit for several hours, can't keep fluids down, and are showing signs of dehydration). But, with out of hospital birth appealing to more and more types of people, sometimes we at our facility feel that a saline lock during labor is prudent.
I think one of the main differences between how it is done with us verusu how it is done in the hospital is that you are still treated like an individual. We don't come in and say "We are inserting a saline lock." Prenatally, your previous births are discussed with you. *You* collaborate with the nurse and midwife, and the decision becomes yours. It isn't something that is randomly done to you. Being a major part of the decision making process certainly makes all the difference, don't you think?!?!
Anyhow, just wanted to give a little info!!!
Hope that helps! Lori