The problem with the due date is that it sounds like there will be consequences if something doesn't happen by then. Everything else with a due date comes with some sort of penalty if we fail to deliver the required materials on time. If you don't return your library books by the due date, you will have to pay a fine. If you don't pay your bills by the due date, there is a late fee, or if it goes long enough, you risk losing the service. If you don't turn in your homework by the due date, you lose credit. If your baby isn't born by the due date... What then?
At your first appointment once you are pregnant, your doctor will ask you what the first day of your last period was. From this date, they add 40 weeks or 280 days. The average gestation of a baby is 38 weeks. This method assumes that everyone ovulates about 2 weeks after the start of their period, around day 12 of their cycles. The first problem with this method is that every woman is different. While many women ovulate around day 12 or 13, not all women do. I, for example, consistently ovulate on day 18 of my cycle, meaning that using this method of calculation would put my due date an entire week off. That is quite significant when you consider how many care providers "won't let" their patients go beyond what they believe to be week 40 or 41.
The second problem with this method is that it is based on averages. Very few people are "average". An average is just taking information from a bunch of people and figuring out the middle of that range. This means that not only could your due date be calculated incorrectly if you ovulate earlier or later in your cycle, but when we say an average gestation is 38 weeks, it just that; an average. Some babies gestate for 36 weeks, or even 40 weeks. In fact, the average gestation for a first baby is 39.5 weeks, not 38. There is about a 5 week range where it is perfectly normal for you to deliver your baby. The due date falls right in the middle because it is an average. By giving a specific date for delivery, we are causing great amounts of anxiety in many women when it doesn't happen on that day.
So, what does happen if we don't deliver on our due date? Most of it is psychological. We are told that our baby will be born on or around this date. Even when doctors say "around" many women take it to mean "on", mainly because it is presented as a "due date". This leads many women to make plans that may or may not work out. Some women are assuming they have time to get things done because "My baby isn't due for another week", but baby decides to come before the due date.
More seriously, we see women who pass their due date and develop anxiety because now "My baby is over due". Psychologically, we are taught that being over due is a bad thing, because now there will be consequences. Perhaps her doctor is putting pressure on her to induce, or her friends and family are hounding her daily asking if she has had her baby yet. This can only serve to increase anxiety and is in no way helpful. If you know someone who is pregnant, try not to pester them if the baby doesn't come "on time".
I have worked with mamas who want their mother to be present at the birth, but she lives out of state, so they arrange for her to be there on the due date. But if baby comes "early", grandma misses it, if the baby comes "late" they sit around for a few days with mama still pregnant until grandma has to leave and misses out meeting her grand baby. I would say, that if you want your mother to be there, but she can't stay for a month, have her come a week or so after the due date you are given. That way if she misses the birth, there is a better chance that she will still get to meet the baby, and help out afterward.
So, if not for a due date, how would you know when to expect your baby? As I stated above, there is about a 5 week range where it is perfectly normal to give birth. Instead of asking for a due date, I would ask for a due month. For example, instead of saying your due date is August 25th, you could say that your baby is due sometime between mid-August and mid-September. This narrows it down to basically the same amount of time that you may be considered "full term". What the date range does, is take away the anxiety if your baby isn't born when you are told to expect them.
I also think that there needs to be a change in vocabulary. Instead of calling it a due date, I prefer terms like estimated time of delivery. That makes it sound less like a bill, and more like a package that will be delivered, and as we all know, sometimes packages arrive ahead of schedule, and sometimes they come late. There is generally less worry over a late package than an overdue bill.