Pregnancy

Due Date Calculations

After the excitement of knowing you are pregnant, and all those emotions and eventful journeys throughout the different trimesters of your pregnancy, labor and delivery is approaching and your early questions about your due date are coming back.

There are a number of handy tools online and through printed media to calculate your due date, more often based on the date of the first day of your last period. However, because some women's cycles are not 28 days and those tools are made for a 28-days cycle, you will need to make a few adjustments before you can calculate if your cycle is longer or shorter.

Although the calculation is not an exact science, you can get an approximated date, because about 96% of babies do not arrive on the calculated due date, regardless which method you use to calculate, and not even the due date given to you by a physician or health care practitioner.

Someone once said that the due date is not the moms or the doctors business because it is up to the baby... and he was probably right, although there are a number of simple calculations that can be used to give you an idea of when the arrival day might occur.

One of those methods is the popular "Count-Back Method", estimating the birth date following a basic mathematical process in which you take the date of the first day of your last menstrual period as the base point, and from that point your add 7 days., and then subtracting 3 months you have the due date.

Another method is the "40-Week method" in which calculation is fairly straightforward as well. Here the base point date is the start of the last menstruation cycle and then the due date is obtained by simply adding 40 weeks from that point. This method is simpler but less accurate because it does not consider that just a few women have a 28-day exact cycle.

With the "266-Day Method", those women with longer or shorter menstrual cycles can receive a more certain degree of accuracy knowing their due date. This is in fact the method used by most physicians, health care practitioners and certified midwives.

Getting the due date consists of an estimation made of the conception date, observing the number of days in a cycle different than 28 days, then adding a count of 266 days projected forward from that point, with lenience of plus or minus 3 days. This number of days is the average gestation period in humans, from conception to birth.

However, all of these calculation methods do not guarantee accuracy and must be amended throughout pregnancy. From week 6 to 10 an ultrasound scan can reveal the size of the baby and other information that will help your physician to find the approximately correct due date.