How to Calculate Pregnancy Due Date with Irregular Periods

Feb 16, 2016

Pregnancy is connected with many signs and symptoms that are associated with the body adjusting to housing a fetus. These symptoms include morning sickness, putting on weight, cravings and food aversions among others. The very important symptom is a lack of menstrual periods. This is because this symptom can be used to estimate a pregnant mother’s due date.

The calculation of the due date from this symptom, however, depends on if you have regular or irregular menstrual cycles. It is easier to calculate a due date when you have regular cycles. A regular menstrual cycle is one where the duration between menstrual cycles is 28 days. But in case of irregular cycles, the following methods can be applied.

The pregnancy wheel

This is a prepared wheel that matches the dates of your last menstrual period with a due date. The estimates for the due date are done by locating the date of the last menstrual period on the wheel, which is in turn matched with a due date. If you have menstrual cycles that are longer than 28 days, which is considered to be an irregular cycle, you need to perform some simple calculations to come up with a proper last monthly period date.

You need to determine roughly how long it takes from the first day of a menstrual period to the start of the next one. The rule of thumb is the second half of a person’s ovulation always lasts for 14 days. The monthly period comes after the 14 days. With this in mind, you can estimate the date of your last menstrual period, hence determine your due date on the pregnancy wheel.

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Dating scan

This is commonly referred to as the ultrasound. It detects the expected due date by measuring the baby’s crown-rump length, which is the length from the baby’s head to its bottom. The crown-rump length is normally fully developed at the 31st week of pregnancy when the baby starts developing their senses. This kind of test is more appropriate during the earlier weeks of pregnancy – when most babies develop at the same rate. In the latter weeks, some babies develop faster than their counterparts.

Online due date calculators

These are found on the websites of various health organizations. They require you to plug in a date for the last menstrual period from which they determine the due date. The date of the last menstrual period can be determined as earlier explained.

It is important to note that none of the methods above is totally accurate. The doctor can at some point change expectant mothers’ due date. However, if the date of the last menstrual period was accurate, an allowance of a week before or after the due date is considered fairly accurate.

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Pregnancy brings joy and expectations. However, it can be a daunting task to determine your due date, especially if you have irregular menstrual cycles. The methods explained above can be applied to determine the due date and remove the worry from a period that is supposed to be exciting.

Although they may not be totally accurate, these methods help a great deal in having a rough due date in mind. This is much better than not having one at all as it enables you to plan and not be caught by surprise when the baby arrives. It also helps keep abreast with the baby’s development milestones as they are in the womb.

The author is a contributor. The opinions expressed are those of the author and do not necessarily reflect the views of Womanitely.