Question - In the United States what % of babies are born:

On their due date?
Due Date +1 Day? Due Date +2 Days? etc. up to 7 days after the due date.
Due Date - 1 Day? Due Date -2 Days? etc. up to 7 days before the due date.

This information can be presented in a table or bell curve format.

The reason I am asking - My wife is pregnant and we are trying to
coordinate travel schedules for out of town family members who will be
visiting us and who have a limited number of vacation days available.
We do not know if it is better for them to arrive earlier or later and
how best to maximize the chances that they will be present for the
birth.  I am sure there are statistics that track the percentage of
babies who are born on their due date, or a day late, two days early,
etc.

Once I have the data I can select the best travel dates for relatives
who have 4 days to visit us and for others who have more days
available.
Thank you.

I did not find the exact information you need; however here is some
material that might interest you:

"Actually, the percentage of babies born exactly on their predicted
due date is so small it's a wonder we bother with due dates at all.
It's perfectly normal for 80 percent of healthy babies to have
anywhere from a 38- to 42-week gestation."

"Robert Mittendord of the University of Chicago Medical Center has
isolated 16 factors that can influence the accuracy of a predicted due
date. Ethnicity may play a role; African-American women, for instance,
often have pregnancies that are, on average, three to eight days
shorter than those of other women. First-time mothers can almost be
counted on to deliver ten days or more after their due date. The
length of gestation seems to peak for babies of mothers who are around
29 years of age, so maternal age may be a factor. Caffeine consumption
makes pregnancies shorter. Taking The Pill up to two months before
conception can cause havoc with due dates. Finally, because biologic
variation in fetal size increases throughout gestation, ultrasound
dating can be deemed somewhat reliable only in the first trimestre."
http://www.mothering.com/articles/pregnancy_birth/birth_preparation/inducing.html


"Most babies are born a week either side of the estimated due date,
but are more likely to come the week after the due date, rather than
the week before."
http://www.birth.com.au/class.asp?class=66&page=4


"However, going over your due date is extremely common. In fact, seven
out of ten babies are born after their due date."
http://www.pregnancy-info.net/labor_inducing_labor.html


"Only five percent of babies decide to greet the world on their due date"
Parents.com 
http://www.parents.com/articles/pregnancy/1037.jsp


"Only 5% of babies are born on their due dates"
The Center for Unhindered Living 
http://www.unhinderedliving.com/downside.html

We faced the same dilemma as you about 2 1/2 years ago. I even posted
the same question as you:
http://answers.google.com/answers/threadview?id=110577

The conclusion we came to is that there is really no way to predict
the birth date. However, any family member travelling to see you would
much rather see a new born then a very pregnant mother to be.  So, we
had people start coming 1 week after the due date so they would almost
definitely have a baby to see even if they weren't there for the
actual birth.  As it turned out, our daughter was born 90 minutes
before her due date!

Your wife probably shouldn't be traveling when she's 9 months
pregnant, anyway. Who wants to be caught in another city, without the
doctor (or midwife) they have grown comfortable with?

Kriswrite

Kriswrite - I believe you have misunderstood the dilemma. He is not
asking about when he and his wife should be travelling, he is asking
when he should have people come to visit him.

You're right, research_help. Would you pass me some coffee, please? :)

Kriswrite

Thank you to everyone who has added comments. I appreciate the assistance.

I may just be that this data does not exist. Though since it should be
as easy to collect as polling 100 or 1000 mothers and asking when they
delivered in relation to their due dates.

I would assume the data would be helpful to hospitals from a
operational planning perspective once they knew who was planning on
delivering at the hospital and when these prospective mother's due
dates might be.

Of course, I'm looking for the data for a much simpler reason.
Traveling dates for relatives who will be visiting us to share in our
child's birthday.

Once again, thank you to everyone who has responded so far, and I'll
leave the question open on the off chance someone can locate this
data.

Greetings Stabo-ga,
It seems apparent that your wife is presently all in favor of having
the greater family near when the baby is born, but I wonder if that
will be the case the day after she delivers.  It's been a long time
since I became a father, so I can't remember, but maybe some of the
ladies here can (recalling the vagaries associated with natural
birth).  If she is still in hospital, it's going to be crowded  - and
in my day, only the father and siblings were allowed to visit.

Personally, as an expectant father, I wouldn't want to have to play
host while my wife was a day or two "overdue" and waiting, and that
could be uncomfortable for the rest of the family too.
Except for the potential grandmothers, I would set a safe date a
couple of weeks later for the family gathering, the christening or
equivalent (or just keeping them waiting till then to learn the
child's name).

Bobbie7-ga, you are the GAR on this question, any personal opinions?

Stabo, take care!
Myoarin

If my relatives were coming to visit me from out of town, I would ask
them to arrive between 2 and 3 weeks after the baby is born. That way,
I would have time to settle in with the baby and I?d be able to enjoy
their visit much more.

This message board about ?Visitors after the baby is born? might interest you.
http://bbs.babycenter.com/board/birthclubs2005/1379764/thread/2054449

I am thoroughly amused by the comments and concede that they have much merit.

Actually I'm of like mind and would prefer fewer relatives in town for
the birth, but on this point I'm conceding to my wife's wishes. All
the relatives who will be visiting will be immediate family as well as
her best girlfriend whose birth my wife attended a couple years ago.

Being a married man, I've learned to pick my battles carefully and in
this case since she's doing all the work, on this point I surrendered
without a whimper. My only stipulation was that I won?t be playing
host. Everyone visiting will have to be somewhat self sufficient since
my wife (and baby) will be getting all my attention.

Back to my original post. I've been tasked with scheduling travel
dates with the expressed goal of maximizing the likelihood that our
guests will be in town (at the hospital, not the delivery room) for
the birth.

I assumed I?d tackle it like a simple math problem. Start with her due
date, find a probability distribution, and then match it up with the
number of days each visitor can stay. Viola, travel dates determined.

It appears that my initial assumption that this data existed may be in
error.  Either it doesn?t, or it appears that it is not something that
is easy to find.

I?ll give it another week and see if anyone can locate an answer. At
that point I have to start booking airline tickets.

Thanks again to everyone who?s contributed

As I mentioned in an earlier comment, I did the same research as you
about 2 1/2 years ago.  It seems that this information doesn't exist. 
The conclusion I found was that "due dates" are not really a
scientific term, just a guess, that can change based on the doctor and
can be changed during the term based on new information learned from
an ultrasound, etc.  A mother may also have more than one due date by
visiting different specialists during the term.

http://www.dogfish.org/chris/fun/delivery.html
Hopefully, you are satisfied with the information the site provides.
Although the sample is from 1986 or even older, I do not think that it
could change recently.
Congratulations for the baby!
minger