Pregnancy Due Date: When will you give Birth?

Accurate Due Date Calculation

Some moms like to know their exact pregnancy due date. Generally speaking, the whole pregnancy process takes around ten months. But to be exact, the entire duration from fertilization to delivery is 280 days. Hence, if you do a 280-day countdown from the first day of your last menstruation period, you will be able to predict accurately your pregnancy due date.

Predicting your Delivery Date (Pregnancy Due Date)

Your Last Menstrual Period

pregnancy due date

When pregnancy is said to take ten months, it is calculated based on a 28-day months or 4-week months. If you are unsure of the fertilization date, it is also possible to predict an accurate due date if you are aware of the ovulation date. Typically, menstrual cycles repeat every 28 days and ovulation occurs 14 days after the start of the last menstrual period.

The pregnancy due date can be calculated by counting down 280 days from the first day of the last menstrual cycle, which adds up to about 40 weeks. Alternatively, you can determine the date of delivery by taking the numerical date of the first day of the last menstrual cycle and add 7. As for the birth month, take the numerical number of the month and subtract 3. For instance, if the first day of the last menstrual cycle were 1 April 2000, the expected due date would be 1 + 7 = 8 and the month of delivery would be 4 – 3 = 1. Hence, the estimated due date would be 8 January 2001. Another way of calculating the due date would be adding 9 to the numerical number of the last menstrual month and adding 7 to the numerical number of the first day of the last menstrual cycle. For example, if the first day of the last menstrual cycle were 1 March 2000, the month of delivery would be 3 + 9 = 12 and the day of delivery would be 1 + 7 = 8. Hence, the expected due date, in this case, would be 8 December 2001.

In reality, most women deliver between 37-42 weeks of pregnancy and hardly on the predicted due date. Approximately 10% of the women experience ‘prolonged pregnancy’ meaning they experience no labor cramps or pain even after two weeks from the predicted due date.

Fetal Size

If you are unable to recall the date of the last menstrual period or experience irregular menstrual cycles, the expected due date may be accurately predicted via ultrasound examination based on the fetal size and development.

For an accurate prediction of the due date, the ultrasound examination must be conducted within 12 weeks of the pregnancy. This is because, after 12 weeks, growth and development of the fetus tend to vary, causing the prediction to be challenging and inaccurate.

Fundal Symphysis Distance (FSD)

Fundal Symphysis Distance is a measure of the size of the uterus used to assess fetal growth and development during pregnancy. It is measured from the top of the mother's uterus to the top of the mother's pubic symphysis. Fundal height, when expressed in centimeters, roughly corresponds to gestational age in weeks between 16 to 36 weeks for a vertex fetus. However, fundal height is only one way of estimating pregnancy stage. It is recommended to factor in the results from ultrasound, fetal movement, etc. to better predict the due date.

Length of Uterus Protrusion

This one is according to the number of months of pregnancy:

4 months – 12 cm

5 months – 15 cm

6 months – 21 cm

7 months – 24 cm

8 months – 27 cm

9 months – 30 cm

10 months – 33 cm

Every woman’s pregnancy due date differ. However, a lot of women give birth on the same day but different times of the day.

Sandra Henderson

Editor-in-chief at Babiology and a proud mother of four passionate about sharing pregnancy and baby growth knowledges

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