Also known as the fetal screening sacan, this detailed scan is offered to all women between the 18th and 22nd week of pregnancy.  At this stage of gestation, your baby has well developed limbs and facial features, and all its major organs and body systems are in place and ready to be assessed.  The scan involves transimitting high-frequency sound waves through your uterus that bounces off the baby, and the returning sounds are converted into an image.  The biggest echoes are from hard tissues, such as bones, which will appear white on the image of the screen, while the soft tissues will appear grey-flecked.  Fluid filled spaces such as the stomach, bladder, blood vessels, and amniotic fluid surrounding the baby will not return sound waves so these are the black spaces in the picture.  It is the difference between echoes and colors that enamble the ultrasonographer to interpret the images.  The Ultrasound starts by checking the fetal heartbeat and then counts the babies-in the case of twins.  Usually it takes about 20 weeks to identify twins.  The head will be measured by circumfrence and diameter.  The abdominal circumfrence and femur are measured as well to make sure the baby is developing in a healthy way.  Any abnormalities of the brain, face, lips, spine abdomen, heart, stomach, kidneys, bladder, and hands and feet will be checked for.  Lastly, the umbilical cord and amniotic fluids will be examined.  You may be able to find out the sex of your baby at this 18-22 week scan, or you can keep it a surprise!  The 18-22 week screening scan can provide a expecting mother with so much information on the progress of her developing fetus.

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