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Second Trimester Ultrasound

An ultrasound examination to assess the fetal anatomy is often recommended by your doctor. This ultrasound has become routine, and almost all women would have this ultrasound performed.

What is the best time to do the second trimester ultrasound?

This ultrasound is best performed at approximately 19 to 20 weeks of pregnancy. Although the examination has in the past been recommended at 18 weeks, the best views are obtained between 19 and 21 weeks.

Do I need a full bladder?

A full bladder is not required for the ultrasound, but some urine in the bladder is often helpful.

What can be detected at the second trimester ultrasound?

An ultrasound at this stage can determine a number of features about your pregnancy.

  1. Demonstrate that the fetus is alive with a normal heartbeat.
  2. Confirm the correct number of weeks of pregnancy by measuring the size of the fetus. This can confirm the due date.
  3. Detect multiple pregnancies (twins, triplets).
  4. Identify the position of the placenta.
  5. Ensure there is a normal amount of amniotic fluid surrounding the baby.
  6. Detect problems within the mother’s ovaries; uterus; or other pelvic structures.
  7. Assess the structure of the fetus, looking for fetal abnormalities.

Will the ultrasound confirm that my baby is “normal”?

Unfortunately, not all fetal abnormalities can be detected by ultrasound. Ultrasound is quite good at detecting a range of structural abnormalities such as spina bifida, limb abnormalities and hydrocephalus (fluid on the brain). Unfortunately conditions such as cerebral palsy and autism cannot be detected before birth as these conditions are related to brain development, rather than structure.

People often ask if the ultrasound will detect cystic fibrosis. Cystic Fibrosis is a common genetic abnormality. It occurs when both parents carry the gene for cystic fibrosis and each parent passes the gene on to their child. Your doctor can perform a simple mouth swab on you and your husband or partner to see if you both carry the cystic fibrosis gene. If you are both carriers then chorionic villous sampling or amniocentesis can be performed to see if your fetus has Cystic Fibrosis. Even if you both carry the Cystic Fibrosis gene there is only a ¼ chance of your baby having the disease.

What will happen if something is found at my ultrasound?

If a problem is detected at the ultrasound then you and your doctor will be informed. Occasionally, another ultrasound in a day or two is required to confirm the diagnosis. With some conditions further testing such as blood tests or an amniocentesis may be required.