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How accurate are dating scans at 13 weeks

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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.

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Early viability scan This usually takes place at 6 to 10 weeks of pregnancy.Ultrasound imaging in pregnancy is widely used to evaluate the baby.It can determine if a baby is present, the position of the fetus and if there is a multiple pregnancy.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.The Royal College of Obstetricians & Gynaecologists (in their 2000 document on Ultrasound Screening), recommend an Early Pregnancy Scan, undertaken before 15 weeks, which can combine the functions of the Early Viability Scan, Nuchal Translucency Scan and dating scan. These two scans are the ‘minimum’ number of scans required during pregnancy and are offered by ¾ of ultrasound units in the UK.Measurements of the fetus will also be taken to ensure it is growing normally.

At this point, should you wish to know the sex of your baby, you can ask the sonographer to tell you.

Transvaginal scanning may also be used to obtain a better image of the womb.

Nuchal translucency scan This is a scan which is usually carried out at 11-13 weeks and is a method of screening for chromosomal abnormalities without having an invasive test such as an amniocentesis.

This is one of the best times to have an ultrasound done as most infants are the same size at this stage of development.

A thorough examination of the fetus’s brain, heart, spine, kidneys, organs and limbs will be carried out and the placenta checked for its position.

Although this is usually fairly accurate, it can not be taken as a guarantee of sex as ultrasound is not 100% accurate.