Ultrasound: Part 2

Although we no longer use X-Rays in the shoe store to check shoe size, it is still the best way to determine if a bone is broken. While ultrasound is not a toy, it is a tool with useful applications in obtaining medical information.

ULTRASOUND IN THE FIRST TRIMESTER

Ultrasound imaging done in the first trimester can determine:

1. the presence of more than one fetus
2. if a miscarriage is happening
3. if the pregnancy is ectopic
4. your due date, to an accuracy of +/- 3 days

If you are very unsure of your dates, you may wish to have a first trimester ultrasound. Dating a pregnancy can also be done as the pregnancy progresses by checking fundal measurement (the length from your pubic bone to the top of your uterus) or by later ultrasound (see below). You and your midwife/doc can discuss what you feel is best for you should any of these situations arise.

ULTRASOUND TESTING AT 18-20 WEEKS

Ultrasound testing done at this time can determine:

1. the presence of more that one fetus
2. the presence of physical abnormalities in the baby better than at any other time
3. cervical length (can be a sign of preterm labor)
4. placental placement (placentas that are across or near the cervix can be noted and monitored)
5. the gender of the baby
6. your due date, to an accuracy of +/- 7 days

If you would like to get one ultrasound during pregnancy to see that “all is well,” this is the best time to do it. All of the baby’s major physical structures have formed by this point. After this point, as the baby becomes more crowded, it becomes harder to view all the structures as well. If your placenta is found to be near or over the cervix, a follow-up ultrasound later in pregnancy will be indicated to make sure the placenta has “moved up” (they usually do). Please note that the accuracy of the due date at this time is +/- 7 days. That means there is a 2 week period in which your baby could be due.

ULTRASOUND TESTING IN THE 3RD TRIMESTER

Ultrasound testing done at this time can determine:

1. if the baby is head-down vs. breech, should that be a concern
2. if you are past your due date, it can confirm that the baby is still doing well and that there is enough amniotic fluid to wait for you to go into labor naturally
3. the presence of more that one fetus
4. the presence of some physical abnormalities in the baby
5. cervical length
6. placental placement and health (making sure it is still working well)
7. your due date, to an accuracy of +/- 3 weeks (a six week range!)

So, if you have one of these reasons listed above, the small risks of ultrasound may be outweighed by the valuable knowledge that can be gained by it.

Remember: Ultrasound is a tool. It is not absolute truth. You can have ultrasound to asure you that all is well, and still have a baby that has an anomoly not found by ultrasound. Conversely, ultrasound can indicate there is a problem when there is none. This is seen most often with estimated size of the baby: It may say the baby is significantly larger or smaller than it actually is.

Ultrasound information is a piece of the puzzle. It is not the whole picture.