Dating ultrasound procedure

WHAT IS A FIRST TRIMESTER ULTRASOUND? First trimester ultrasound is performed in the first months of a pregnancy.
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Ultrasound: Sonogram

The transvaginal ultrasound probe is thin, about 2cm diameter. The probe is covered with a disposable protective sheath. A small amount of ultrasound gel is placed on the end of this probe. The probe is then gently inserted a short distance into the vagina. All transvaginal probes have been cleaned and sterilised according to recommended protocols.

Performing the transvaginal ultrasound usually causes less discomfort than a pap smear. No analgesia is required for this ultrasound. Your privacy will always be respected during your ultrasound, especially the transvaginal examination.


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You will have a large towel covering your lower body, in addition to wearing a gown during the transvaginal ultrasound. You will always have a choice about whether transvaginal ultrasound is performed. If you have concerns about transvaginal ultrasound, please discuss this with your sonographer before your ultrasound begins.

Dating ultrasound procedure

We usually get better images during transabdominal ultrasound if the bladder is partially filled, so to help your examination we ask you to drink water prior to the assessment. Please empty your bladder 1 hour before your appointment, drink 2 glasses of water and try not to empty your bladder again until after your appointment. A full bladder moves bowel out from the pelvis into the abdomen, helping visualisation of the pregnancy, uterus and ovaries.

Your bladder should not be so full that it causes pain. If your bladder is very full and painful, you should empty a small amount so you are more comfortable. You will be able to empty your bladder after the transabdominal ultrasound is completed and before the transvaginal ultrasound begins if transvaginal ultrasound is required. Sometimes the results of a first trimester scan may be inconclusive or uncertain, and need to be combined with your clinical history and blood tests serum BhCG. Some women need to return for another ultrasound scan a few weeks later to assess the progress of the pregnancy, or they may require another blood test serial serum BhCG.

We realise this is often an anxious time for parents, while they wait for the next ultrasound to check on their baby. We will do our best to answer your questions and minimise your anxiety. A first trimester ultrasound will usually include each of the following components however some ultrasounds may focus more on particular areas. Your ultrasound is always performed in the context of your clinical history and the results of previous ultrasounds and investigations.

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Before 5 weeks gestation, the developing pregnancy is too small to detect on ultrasound. The endometrium the lining of the uterus where the pregnancy will grow should appear thick and secretory. One of the ovaries will have an ovulation cyst called a haemorrhagic corpus luteum. This ovarian cyst is a normal part of getting pregnant, as the egg forming your baby was released from this cyst.

Dating ultrasound procedure - Single Pattern

The corpus luteum will gradually resolve get smaller as the pregnancy continues. At weeks gestation, a small gestation pregnancy sac is seen within the uterus. A transvaginal ultrasound is usually required to see the baby at this stage of the pregnancy. Your baby is just a tiny embryo. The sonographer will put gel on your abdomen and move a hand-held device called a transducer, back and forward over your skin.

In some situations, such as when the scan is completed before 10 weeks of gestation or you are overweight, you may also need a vaginal scan. Your sonographer will let you know if this is needed. For an abdominal dating ultrasound, you will need to have a full bladder. You may be asked to drink some water and not go to the toilet beforehand because a full bladder helps to push your womb up to give a better picture. For a vaginal scan, you can have an empty bladder. This will provide a fairly accurate estimate of how many weeks pregnant you are.

But it is important to remember that only a few women go into labour on their due date, so it can be more helpful to think about the month in which you are expecting your baby, rather than the exact day. Information on pregnancy ultrasound scans including when they are taken, what it can be used for, dating scans, anomaly scans, plus links to trusted resources. This Dads Guide to Pregnancy article covers early pregnancy scans and screening, plus normal fetal development and early miscarriage for men, by men.

In the second trimester of pregnancy, you may be offered to have an morphology scan anomaly scan. Learn about what it looks for and when it is performed.

How is a dating scan performed?

A nuchal translucency scan is part of the ultrasound scan that may give an indication of chromosomal abnormality. Learn more about how and when it is performed. During your pregnancy, you will be offered a number of tests and scans. The aim is always to check on the health of you and your baby, but it can sometimes be overwhelming and confusing. Handy infographic that shows what you can expect at each antenatal appointment during your pregnancy.

In the meantime, we will continue to update and add content to Pregnancy, Birth and Baby to meet your information needs. Your little one will also start to make involuntary movements, similar to a slight flicker or a jump. Join Huggies now to receive week by week pregnancy newsletters. Pregnancy Week by Week Take a look at each week of your pregnancy, from conception to birth, with our comprehensive email newsletters. You'll need to activate to enter promotions - find out more. Didn't get the email? What best describes you?

The very first ultrasound! :)

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