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5 Reasons behind the Timing for Ultrasounds

Everyone, young and old, seems to find joy in seeing the waving hand of a fetus inside the uterus. There’s something magical about being able to see inside the private quarters of a developing human being. But, as fascinating as it can be, we get a lot of questions about ultrasound from our patients.

Patients often ask if their doctors are recommending too many ultrasounds. Ultrasound technology does not use radiation and no risks have surfaced in over 40 years of use in obstetrics. The information you can get from an ultrasound has revolutionized obstetrical medicine, and those who use it daily can’t imagine an era without it. But, ultrasound in the wrong hands is dangerous.

Highly trained professionals know how to operate the equipment safely so that doing the ultrasound doesn’t pose any harm to the developing baby. You may have heard of celebrities who buy their own (very costly) ultrasound machine to use at home throughout their pregnancy so that they can see their baby whenever they want. Don't even think about it! Using this technology without training and with the wrong settings could cause harm to the pregnancy; especially if repeated frequently.

Most providers of prenatal care have their own preferences for when and how many ultrasounds to order for their patients. They also have a rationale for their preferences.

Not all of these scans are done everywhere, and practices vary throughout the country. Also, some insurance companies will only cover a set number of ultrasounds, so your doctor will have to choose which ones are most important for you.

Confirming viability

An ultrasound at 6–10 weeks is helpful to confirm the viability of the pregnancy. This is the most accurate time to date the pregnancy — plus or minus three days from the actual date of conception.

Testing for early issues

The first trimester screen for chromosomal problems is done between 11 and 13-1/2 weeks. It is done at that time because the nuchal translucency, part of the screen, can be most accurately measured.

Scanning for birth defects

An “early anatomy” scan is sometimes done around 16–18 weeks. Many obvious and serious birth defects can be seen at that time, but the detail of the ultrasound, or resolution, is not as good as it is a few weeks later. The reason some providers do this early scan is so that patients can find out early if they have a significant problem, in time to make some decisions about how to manage the rest their pregnancy.

Conducting an anatomy scan

The routine anatomy scan is typically done around 20–22 weeks. The level of detail that can be seen with modern equipment is amazing. Most serious birth defects can be diagnosed at this time by experienced sonographers. If, however, you do find out that your baby has a serious birth defect, you have less time to make decisions about continuing the pregnancy. It is also emotionally more difficult to deal with because the pregnancy is half over by then, and most women have developed a significant bond with their baby.

Planning for delivery

Finally, many providers will recommend an ultrasound in the third trimester, around 32–36 weeks, to get an estimate of the size of the baby so that they can plan for delivery appropriately. If the baby is too large or too small, or if the amount of amniotic fluid is too high or too low, your provider will likely do additional testing and may move your delivery date up.

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