There are two issues here. One is you are getting tired of having to respond politely to people who want to help. You would probably prefer it if people would simply stop asking. However, that's probably not going to happen. Put the shoe on the other foot. If you knew someone in your position, would you not like to offer help? So getting individuals to stop asking probably isn't going to happen.
That said, you say, "My neighbors have refused to allow me to mow my lawn." Whoa, these are NEIGHBORS. There is no way they can mow your lawn without your permission. When you say, "I've been polite," you indicate that your "No, thank you" may be so weak as to be ineffective. This is your house, your life, your pregnancy. You do not have to accept others' generosity if you don't want to.
Let's say someone says, "I'd like to make some dinners for you to have in your freezer."
"I appreciate your intention, but no thank you."
"Oh, but really, it's no trouble. I'd like to do it."
"Thank you but no."
"How about if I just make up one or two."
"Thank you but no."
Get the idea? Hopefully the helpful person will as well.
It's really difficult to say "No" without giving an explanation and also mean it. I think we teach people how to treat us and your neighbors at least, have learned that when you say No, you don't mean it. If you really don't want people doing things to help, then you need to stand up and just keep saying "No," until they get it.
Another thing to think about though is giving a bit. For instance, are there things you might want help with once the baby is born? Maybe you'd like help with laundry or babysitting or fresh veggies from someone's garden. Offering an alternative to anyone who would like to help creates a win-win situation.
My guess is that you will come to a place where you can use some help and by thanking people for their generous offer but adding something like, I'll bet I will be able to use some help once the baby comes, so I'll call you, will be useful.
Finally, I think that all this needs to be said in a tone of real appreciation. I have many clients who would be grateful for ANYONE to step forward and offer a hand. Reciprocate someone's generous offer in a way that is clear, confident, yet kind.
Hope some of this helps.
Warmly,
L.
www.CoachWithLynn.com