How to Read Pregnancy Sonograms

Written by lauren farrelly
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Trying to read pregnancy sonograms can be tricky, depending on the stage of the pregnancy. The earlier the pregnancy is, the less defined many of the features will be. However, later in the pregnancy, you will be able to see specific features such as fingers, toes, mouth, ears and eyes. In addition, you will typically be able to determine the baby's sex after the 16th week of pregnancy on an ultrasound.

Skill level:
Moderately Challenging

Things you need

  • Sonogram printout/photo

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  1. 1

    Obtain an ultrasound from your OB/GYN office. They will have a sonogram technician skilled to conduct the sonogram and they will print out various photos and angles of the baby for you.

  2. 2

    Measure the crown-rump length (CRL). The top of the head to the bottom part of the foetus, or feet, will be measured in millimetres on the sonogram. This will determine gestational age of the foetus. It's useful when women are not able to remember their last menstrual period, which is a factor in determining the date of conception. Determining the crown-rump length will help determine an estimated due date for the baby.

  3. 3

    Measure the biparietal diameter, which is the diameter of the two sides of the head. This measurement is taken after the 13-week mark, and continually taken throughout pregnancy to be sure the baby is developing correctly. At 13 weeks, the biparietal diameter is typically around 2.4 cm, and it will end up around 9.5 cm at birth.

  4. 4

    Determine the length of the baby's femur. The femur is the longest bone in the body and will help determine how far along the pregnancy is. The femur is about 1.5 cm at 14 weeks and about 7.8 cm at birth.

  5. 5

    Measure the abdominal circumference. The abdominal circumference is a measurement taken on the ultrasound of the abdomen of the baby (around the belly button). This measurement is done much later in the pregnancy to predict the baby's length and weight. This measurement is used to determine not the age of the foetus, but rather the size of the baby, which differs from pregnancy to pregnancy.

  6. 6

    You may be able to detect malformations in the foetus before the 20-week mark. An absence of the fetal nasal bone (a distinct nasal feature on the foetus) or a large thickness at the back of the neck may signal Down Syndrome.

  7. 7

    Determine the baby's sex. This may be a little trickier depending on the foetus position when the ultrasound is taken. On the baby's genitalia, a girl will be signified by 3 faint lines. A boy will be signified by a penis, but on the ultrasound it will look more like a turtle - the penis will be rounded with a small tip on the end.

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