Do dating scans measure from conception

Pregnancy can be measured in two different ways. The most common and most often used in clinical obstetrics is the measurement of the gestational age of the pregnancy. The gestational age of the pregnancy is measured from the first day of the last menstrual period.

Calculating Conception Date

In this way of dating the pregnancy, the pregnancy is 40 weeks in duration on average instead of the actual 38 weeks. In other words, it dates the pregnancy, on average, two weeks longer than it is. The other way of measuring the dates of the pregnancy is to measure the fetal age. The fetal age of the pregnancy is measured from the time of conception or the estimated time of conception ETC.

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When measuring the pregnancy in this fashion, it will be 38 weeks long or two weeks shorter than the gestational age dates. The fetal age, of course, is the actual age of the pregnancy. Historically, the obstetrician has focused on the first day of the last menstrual period for two reasons. First of all, the menstrual flow itself is a fairly dramatic symptom which the woman can be expected to remember. In addition, it is easy to teach her to record the first day of the last menstrual period so that when that information is elicited by the physician, at a later time, it is available.

How can I know when I conceived?

However, in the midst of all of this, the obstetrician and many women have missed the point that the cervical mucus discharge is very much a flow in the same fashion as the menstrual flow. In some countries, they refer to menstruation as the red flow and the mucus discharge as the white flow. Unfortunately, modern obstetrics has paid little attention to the white flow. Therefore, one can date the pregnancy according to its true date or true beginning or in fetal age terms.

This is measured by evaluating the acts of intercourse that occur during the time of fertility and establishing an estimated time of conception through this approach.

Calculating Conception - American Pregnancy Association

Then at the week scan I got an EDD of 15 march, so that early scan was completely out. Well, you'd think so, wouldn't you. At around 12 weeks you can get more accurate measurements. By talking to the health care professionals you should get a clearer picture as to what is happening. Thanks so much for your post — we always welcome feedback, positive or negative, as we always aim to make our articles as accurate and as helpful as possible. We spent a lot of time talking to sonographers before writing this article, so we're surprised that you think what they're saying is not in line with what you have studied.

We'd be really keen to know more about your studies — and what you have learned. You're right that we did include 'anecdotal stories' in our article. We used them to illustrate the key points we were making in the articles but the quotes we used were all centred on the real experiences of pregnant women posting in our forum.

We are confident that we are not using these quotes to 'misinform women', as the key points in our article were all sourced from expert monographers. It's interesting that you say that ultrasounds between 8 and 10 weeks are the most accurate. In the UK, most pregnant women don't have an ultrasound until they are at least 12 weeks pregnant.


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Perhaps you are based in the US, or another country, where ultrasound practice is a bit different? We use cookies to improve your experience of our website. Skip to main content. Find us on YouTube Twitter Pinterest.

Can your pregnancy scan give the wrong due date? Some of the information in this article disagrees with everything we have studied so far regarding dating pregnancies and ultrasound accuracy. An ultrasound between weeks is the most accurate, not Please do not misinform women on anectodal stories.

Do drop us a line a bout your studies, please. We'd be really interested to hear more.

How do they work out due date from dating scan

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