First trimester ultrasound dating.

 

Correct measurements in the first trimester are crucial to have an accurate due date, so here I will explain all you need to know about First trimester ultrasound, measurements, dating and guidelines.

As you probably know accurate pregnancy dating is important for diagnostic and management during pregnancy. Sometimes dating by last menstrual period is less reliable than dating by ultrasound. Basically Dating by first trimester ultrasound, via the crown-rump length, has a 95% confidence range of ±5 days, slightly better than the ±8 days for dating by second trimester ultrasound at 14–20 weeks. This small difference appears to be too small to justify a routine first trimester scan for the purpose of dating the pregnancy.

First trimester ultrasound, measurements, dating and guidelines.

In the previous post I explained more in deep about HCG levels in the first trimester and when are you expected to see an intrauterine pregnancy, HCG is also important on the process of dating your pregnancy and provide an accurate due date as well.

So assuming that on your first scan only the Gestational SAC was seen which is normal at a 5 week ultrasound, then the gestational sac dimensions are taken and that will give us an idea of how far the pregnancy is.

First trimester ultrasound measurements.

However is not until we measure the Crown rump length (CRL) that the DUE DATE is set, here is why…

The most accurate sonographic measurement correlating with menstrual dates is the CRL, this measurement (the crown rump length or CRL) is the maximum visible length of the embryo, care must be taken not to include the umbilical cord or yolk sac in the CRL measurement.

Embryonic CRL measurement is more accurate than using Last menstrual period dates or physical exam in dating a pregnancy, remember if you suffer from Irregular periods due to PCOS or any other conditions then more likely Ultrasounds measurement are going to be different from your gestational age.

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The guidelines for dating your pregnancy consist in comparing Crown rump length ( CRL )  and the menstrual age. Basically if there is a discrepancy of 5 days between the CRL and the gestational age, and you are 8 weeks or less, the Due date will be set with the CRL Measurement, take a look on the table below.

Remember as soon as we see an embryo we can measure a heartbeat. Normal ranges are from 115 to 160 beats per minute. Varies thought out the pregnancy. It increases at around 10 weeks to 150 to 175 beats per minute and, decreases again approaching to term to 130 beats per minute.

Related posts.

Pregnancy diet. What to eat or what to avoid during pregnancy.

First trimester must do’s to achieve a healthy pregnancy.

Ways to relieve morning sickness during pregnancy.

Final thoughts about First trimester ultrasound dating.

This is the most important information about Dating your pregnancy. Next post will be about Abnormal first trimester ultrasound, I will talk about Anembryonic pregnancy or Blighted ovum, Embryonic demise, and a quick review about Ectopic pregnancy and more, I’ll see you next time.

Zadi, xo.

Disclaimer: Due to HIPPA compliance and regulations all patient information is protected on this site. Also the information provided on my blog is designed to provide helpful information about the topic and are made with the best of my knowledge therefore is not intended to diagnose or treat any medical condition, For diagnosis or treatments on any medical problems consult your own physician. The author is not responsible or liable for any mistreated pathologies or wrong treatments.