What is us obstetric dating scan

It can also help to diagnose abnormalities or problems, help determine the age of the pregnancy and subsequent due date as well as showing the position of the placenta in relation to the birth canal. There is also then a routine scan at 20 weeks.

Obstetric (Pregnancy) | BMUS

Individual circumstances may dictate that more scans may be offered and a breakdown of what you could receive is detailed below. This usually takes place at 6 to 10 weeks of pregnancy. The scan can confirm the number of babies in the uterus, the embryo can be observed and measured by about five and a half weeks and a heartbeat usually detected by 6 weeks.

Introduction to Transvaginal Ultrasound Scanning-Part II

Scans at this stage in pregnancy are reassuring for women experiencing bleeding, pain or who have had previous miscarriages. Transvaginal scanning may also be used to obtain a better image of the womb. This is a scan which is usually carried out at weeks and is a method of screening for chromosomal abnormalities without having an invasive test such as an amniocentesis. Gestational age is usually determined by the date of the woman's last menstrual period - assuming ovulation occurred on day fourteen of the menstrual cycle.


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Ultrasound scans offer an alternative method of estimating gestational age. The most accurate measurement for dating is the crown-rump length of the fetus, which can be done between 7 and 13 weeks of gestation. After 13 weeks gestation, the fetal age may be estimated by the diameter of the head and the length of the femur.

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Dating is more accurate when done early in the pregnancy. When a later scan gives a different estimate of gestational age, the estimated age is not normally changed but rather it is assumed the fetus is not growing at the expected rate. This scan is a routine scan in the UK which takes place at around 20 weeks. This is one of the best times to have an ultrasound done as most infants are the same size at this stage of development. We like you to have a full bladder as it makes it easier for us to see your uterus and ovaries from across your tummy.

7 Week Ultrasound

We also have a look at your kidneys as occasionally the baby can lie on your ureter which drains the urine from your kidneys causing you some problems later in the pregnancy. So we like to know your kidneys are normal at the start of your pregnancy so if a problem arises later we know it is your baby causing the issue! After we scan across your tummy we will then send you to empty your bladder.

We like to do a vaginal scan as this gives us better visualization of your developing baby and where the pregnancy is developing in your uterus. You will be able to see the difference in the clarity of the scan across your tummy compared to a vaginal scan on our wall-mounted monitors. After your scan the sonographer will leave the room to discuss the images with the radiologist or obstetrician who may require more images to be performed.

This is normal practice and nothing to be alarmed about.

Why would I have a dating scan?

Once you have been given your expected due date at your dating scan, the next scan will be the week scan. Log in to view your images online Search. Home What we do Obstetrics Dating Scan. This is an ultrasound scan that is performed early in the pregnancy. What to expect on the day? The scan takes 30 minutes to perform.

You will be called by the sonographer who will take you to the scanning room. Please come with a full bladder which will make it easier to obtain images of the uterus. Risks Ultrasound is safe to use throughout your pregnancy.

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Benefits You will be able to get your expected due date of your baby on the day. You will be made aware if there is anything of concern on the day. If you have any questions you will be able to ask our on-site radiologist. Common questions about this scan What is an Ultrasound scan? Will my baby be ok during the scan? Do I need to do anything before I have this scan?


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  • Obstetric (Pregnancy)?
  • Your pregnancy and baby guide.
  • How long will the scan take? The scan will take up to 30 minutes on the day. What happens on the day? You will lie down with your tummy exposed and a towel tucked into your pants. The images of the examination will be provided on a USB stick for you to take away with you. Other obstetric scans Once you have been given your expected due date at your dating scan, the next scan will be the week scan.

    How is a dating scan performed?

    Important things to know The scan takes up to 30 minutes to perform. You will be told your expected due date before leaving.