Pregnancy Due Date
How To Calculate Your Baby's Delivery Date

estimating your due date

Estimating due date

Estimating Your Due Date


Calculation Based On Conception
Ovulation/Last Period
Problem of Irregular Periods
Using an Ultrasound Scan
Babies Not Born On Their Due Date
Keeping An Ovulation Calendar

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Pregnancy Guide

How To Calculate Due Date Based On Conception

On average, a pregnancy lasts 266 days (38 weeks) from the date of conception (see: pregnancy trimesters). If you know which day you conceived, then the calculation is straight forward. If for example you conceived on June 1, then your due date (266 days later) is February 22 the following year. An Aquarius baby! As few babies arrive on time however, a delivery date could stretch to 2 weeks either side of this date.

Based On Ovulation/Last Period

As it is not always possible to pinpoint the day of conception, another calculation is based on ovulation. With this method the due date is generally calculated as 40 weeks from the start of your last period. The assumption here is that ovulation took place roughly 2 weeks before your period, which is the most likely time for conception. Using the example of June 1 as the first day of your last period, this would give a due date of March 8. This calculation may be more accurate if you maintain an ovulation calendar for a few months beforehand.

How To Calculate With Irregular Periods

If your menstruation cycle is not regular, say you only get your period every 6 or 7 weeks, then you may find this calculation more suitable. You subtract 3 months from the first day of your last period and then add 7 days. So for example, if your last period began on June 1, subtract 3 months which leaves you at March 1. Then add 7 days, which leaves you at March 8. So your due date is March 8, the following year.

Calculating With An Ultrasound Scan

If these calculations do not appear like an exact science, you are right! Ultimately an abdominal examination and pregnancy ultrasound to measure the baby in the womb is a more accurate way to date your pregnancy. Some OB/GYNs perform early scans as part of routine prenatal visits, but others will only recommend one if the mother's periods are irregular and the due date cannot be estimated based on the last menstrual period (LMP). Some also offer scans if the woman has a history of miscarriages or pregnancy problems. Women experiencing a pregnancy after the age of 35 will also be screened more carefully.

Babies Not Born on Their Due Date

Most studies show that only one in 20 babies are born on their due date. This is further compounded by the fact that a normal pregnancy can last anywhere between 38 and 42 weeks – which means you will be kept guessing right up to the delivery day! This is the reason why the medical term for due date is EDD, or estimated delivery date. Consequently there is no need to panic if your baby does not arrive bang on schedule. Babies are considered full term after week 37 of pregnancy and not overdue until after week 42.

Other dates to keep in mind which are milestones of pregnancy progress include:
9-12 Weeks: First time the fetal heartbeat can be heard with a Doppler.
16-22 Weeks: First flutter, and first time you will feel life.

Keeping An Ovulation Calendar

If you are trying for a baby, it is helpful to track your ovulation dates in order to more accurately establish your due date when you do fall pregnant. You can do this by keeping an ovulation calendar and tracking your menstrual cycle. Other methods include keeping track of your basal body temperature and any changes in consistency of cervical mucus (the gooey stuff that gets in your panties). Or, you can use an ovulation predictor kit (OPK) which can pinpoint ovulation 12 to 24 hours in advance by measuring levels of luteinizing hormone (LH) in your urine.

  Related Articles on PREGNANCY

For more on planning for a new baby, see the following:

Pregnancy Tips: Advice on all aspects of pregnancy.
Prenatal Care Guidelines: Particularly useful for new moms to be.
Estimating Prenatal Care Costs: Adding all the expenses up.
Paternity Tests: If there is any doubt about paternity.

Return to homepage: Womens Health Advice

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