Ultrasound

What is an ultrasound?

An ultrasound (also called a sonogram) is a noninvasive diagnostic test that uses sound waves to create a visual image of your baby, placenta, and uterus, as well as other pelvic organs.

It allows your healthcare practitioner to gather valuable information about the progress of your pregnancy and your baby's health.During the test, an ultrasound technician (sonographer) transmits high-frequency sound waves through your uterus that bounce off your baby. A computer then translates the echoing sounds into video images that reveal your baby's shape, position, and movements. The series of television-monitor images is called a sonogram.

The words ultrasound and sonogram are often used interchangeably. (Ultrasound waves are also used in the handheld instrument called a Doppler that your practitioner uses during your prenatal visits to listen to your baby's heartbeat.)

Most moms-to-be have a standard ultrasound when they're between 16 and 20 weeks pregnant. But you may have one as early as 4 or 5 weeks or any time after that if there are signs of a problem. Most people look forward to the midpregnancy ultrasound because it gives them a first glimpse of their baby. The technician will probably present you with a grainy printout of the sonogram as a keepsake. And you may be able to find out your child's sex, if you want to. But the main purpose of the ultrasound is to provide you and your practitioner with important information about your baby's health and development.

If you're having a low-risk pregnancy, however, you might not be offered an ultrasound at all. In fact, the American College of Obstetricians and Gynecologists recommends ultrasounds only when there's a specific medical reason.

When will I have my first ultrasound scan?

All women are offered ultrasound scans in pregnancy, but the number and the timing seems to vary considerably between different areas. As a general guide they include:
• an early scan at 6-10 weeks, sometimes using vaginal scanning techniques
• dating scans at about 10-14 weeks
• nuchal translucency scans at around 11-14 weeks
• mid-trimester scans at 18-21 weeks

Some hospitals will also offer private scans for a fee to women who live both locally or outside their area.

Early scan - if you have previously miscarried or you have had bleeding in the first few weeks of this pregnancy, you may be offered an early scan between 6-10 weeks. This is to reassure you and end the uncertainty of not knowing if your pregnancy is OK. This scan may be done using a probe placed inside the vagina, instead of the usual abdominal scanning equipment. This is called "transvaginal ultrasonography". Many hospitals now have early pregnancy clinics which run daily so your midwife can refer you straight away. It's natural to feel a little anxious about having a vaginal scan. If you do feel anxious, you should discuss it with the nurse or sonographer beforehand. It's also a good idea to take someone else along with you. If it helps, you could also ask for a woman to carry out the scan. The vaginal scan will give a clearer picture of your baby earlier in pregnancy than an abdominal scan.

Dating scan - it is now recommended that all pregnant women have a dating scan, ideally at about 10 to 14 weeks of pregnancy. This is needed if you are planning to have blood screening tests for Down's syndrome and/or spina bifida. (It is important to know the exact number of weeks and days of pregnancy at the time the blood test is taken so that the results of the test can be accurately interpreted.) This scan is also a more accurate way of establishing your due date than counting from your last monthly period (LMP). It can also find out if you are having more than one baby.

Nuchal translucency (marker) scans - all women should now be offered a nuchal translucency scan between 11 and 14 weeks of pregnancy which can estimate the likelihood that your baby has Down's syndrome. It's usually offered as part of the "combined test", which includes the nuchal translucency scan and a blood test to detect the levels of the pregnancy hormone human chorionic gonadotrophin (hCG)and pregnancy-associated plasma protein-A. For a definite diagnosis a diagnostic test, such as amniocentesis, is needed. Not all hospitals have staff trained for this particular skill at present, but it is fast becoming more available in NHS hospitals as an alternative to blood screening tests.

Mid-trimester scan - this scan is offered to all pregnant mums between 18 and 21 weeks. The main purpose of this scan is to examine your baby closely and check for abnormalities. The scan can show your baby in fine detail. You will be able to see movements and some hospitals will tell you the sex of your baby if you wish to know. So when is the best time to have a scan? This is going to depend on your own individual situation and on what's available in your local area.

If you have reason to be worried about your pregnancy in the early weeks, then an early scan may be a good idea. If you are not sure of your due date, or you are planning to have blood screening tests, you may need to have a dating scan. If nuchal scans are available near you (either on the NHS or privately), you may choose to have one of these at around 12 weeks. It may be that the only scan you need or want during your pregnancy is the mid-trimester scan at around 20 weeks.