How Is Your Due Date Determined?

Dr. Barra O'Briain, MD, discusses How Is Your Due Date Determined?

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Dr. Barra O'Briain, MD, discusses How Is Your Due Date Determined?
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Video transcript

Featuring Dr. Barra O'Briain, MD
Duration: 2 minutes, 23 seconds

The due date is determined most commonly by using the first day of your last menstrual period.

And the due date is exactly 40 weeks from that time or 280 days from that time. We also use ultrasounds to determine the due date because sometimes the due dates do vary between the two and the causes of that most commonly is the implantation bleed when the baby or the little fetus is implanting into the wall of the uterus can cause a bleed and that can be misinterpreted as your last menstrual period.

Long or short periods or irregular periods are also a cause of discrepancies between the last menstrual period from ultrasound and from dating. Bleeding of any kind that is not necessarily menstrual can confuse the dates.

Dating scans are often done between 8 and 11, 12 weeks. And if there's a discrepancy more than 5, 7 days, we would use the ultrasound dating as opposed to the due date, uh, determined by dating.

Due dates are important not directly with regards to the due date itself because very few women will actually deliver on their due date.

We define term, that period of time where women are expected or often have their pregnancies where the pregnancy is basically ready to be delivered, the baby is ready to be delivered. Term is defined between 37 and 42 weeks of pregnancy.

And so that five-week period is put on a calendar that we all know and use by the due date itself. And so it's more important for us as clinicians to know when 37 weeks and 42 weeks of pregnancy is rather than when the actual due date occurs.

And so that block of time is what we need to know. If you have any concerns with regards to what is your due date and which date to use, or if you're pregnant and gone past your due date and have concerns, contact your obstetrician, family doctor, or midwife that is caring for you during the pregnancy.

Presenter: Dr. Barra O'Briain, Family Doctor, Vancouver, BC

Local Practitioners: Family Doctor

This content is for informational purposes only, and is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified healthcare professional with any questions you may have regarding a medical condition.