Early ultrasound dating off

The images below will give you an idea of what can be seen and what they look for at each week; of the first trimester.The gestational sac first appears at about 4 weeks gestational age, and grows at a rate of about 1 mm a day through the 9th week of pregnancy.While your sonographer takes measurments they will explain what you are looking at.It may not be easy for you to make out what you are seeing on the screen in the early scans.

A common method is to measure the mean sac diameter (MSD), add 30 to the sac size in millimeters, to give gestational age in days.It is recommended that all pregnant women have a scan in the first trimester, to establish the date when the baby is due, check the number of babies also the position of the placenta.First trimester ultrasonic scans may show 'soft' markers for chromosomal abnormalities, such as the absence of fetal nasal bone or an increased fetal nuchal translucency (back of the neck) to enable detection of Down syndrome fetuses.Measurements taken at these early scans will help to; confirm a pregnancy, date the pregnancy and to see any problems that may occur in the pregnancy ( low lying placenta, twins etc.).Scans in early pregnancy are usually performed in the first trimester around 12 weeks.