As you have read, there are many risks linked to extended ultrasound and sonogram exposure while pregnant. I wanted to take a moment to explain the differences between the sonograms out there, and everything you will learn if you elect to have one performed. Your midwife or doctor may recommend one or more of the following:
- Dating Scan: A dating scan is an ultrasound examination which is performed in order to establish the gestational age of the pregnancy. If you or your doctor/midwife is unsure of the date of your last menstrual cycle, if you have had any bleeding, are unsure of when you conceived or your estimated due date, you will receive a dating sonogram. This ultrasound will show you exactly how far along you are, and can see the start of a pregnancy as early as 4 weeks and 3 days along (but some pregnancy cannot be seen until 5 weeks). You will see the beginnings of a gestational sac, but no heartbeat or further fetal development yet at this stage. An embryo and fetal heartbeat can be detected as early as 6 weeks and 3 days, but may not be picked up until further along. You will also know the location of your pregnancy. If there is a chance that it is ectopic, you will find out now. At this stage of pregnancy, the dating scan will be done transvaginally, meaning the ultrasound wand will be inserted into the vagina to see the pregnancy. A dating scan can determine the number of gestational sacs present (which may decrease by the end of the 1st trimester, if there is more than one). Your cervix, uterus position, and ovaries will also be seen, and you will learn if there is any clotting or fibroids. A sonogram done before 9 weeks will be the most accurate to use for dating the pregnancy.
- Breakdown of what can be seen:
- at 5 ½ weeks gestation a tiny sac can be seen in the uterus, but the baby and its heart beat may not be detected yet. 5 ½ weeks gestation means 5 ½ weeks from the first day of the last menstrual period, which is usually about 3 ½ weeks from the date of conception (confusing, isn’t it!)
- By 6 to 7 weeks gestation, the fetus is clearly seen on trans-vaginal ultrasound and the heart beat can be seen at this early stage (90 to 110 beats per minute under 6 to 7 weeks, then 110 to 200 beats per minute as the baby matures).
- By 8 weeks gestation the baby and its heart beat can be detected relatively easily with trans-abdominal and trans-vaginal examination.
- 1st Trimester Scan (Also known as a NT Scan): Having a transabdominal sonogram between 12-13 weeks is performed to confirm your baby’s heartbeat and conclude first trimester screening for chromosomal abnormalities. The screening is optional for one or all of the following: Down’s syndrome, Edwards’ syndrome and Patau’s syndrome. Down’s syndrome is also called Trisomy 21 or T21. Edwards’ syndrome is also called Trisomy 18 or T18, and Patau’s syndrome is also called Trisomy 13 or T13. The screening test offered at 11-14 weeks is called the combined test. It involves a blood test and an ultrasound scan. If a screening test shows that you have a higher risk of having a baby with Down’s, Edwards’ or Patau’s syndromes, you will be offered diagnostic tests to find out for certain if your baby has the condition. In addition to screening for these abnormalities, a portion of the test (known as the nuchal translucency) can assist in identifying other significant fetal abnormalities, such as cardiac disorders. The screening test does not detect neural tube defects. The combined accuracy rate for the screen to detect the chromosomal abnormalities mentioned above is approximately 85% with a false positive rate of 5%. A positive test means you have a 1/100 to 1/300 chance of experiencing one of the abnormalities. http://www.isuog.org/nr/rdonlyres/9225e408-c904-4a7f-84ae-812e456fbddd/0/isuog1sttguidelines2013.pdf and http://www.nhs.uk/Conditions/pregnancy-and-baby/pages/screening-amniocentesis-downs-syndrome.aspx#close
- Anatomy Scan: Between 18-21 weeks, you will have a more in-depth ultrasound done to determine the baby’s size, weight and to measure growth ensuring the fetus is developing according to plan. In addition, the anatomic ultrasound looks at and takes measurements of many different anatomic parts of the fetus. The technician or the doctor will be looking for any signs of slower than normal development. The skeleton should be hardening at this point and the sex of the baby may be visible. In many cases, the baby may have their legs crossed or be facing away from the abdomen and thus the sexual organs will not be visible during the anatomic ultrasound. But fingers crossed, you will learn the gender! You will receive many pictures of you your little one during this scan! The following fetal parts are checked during the anatomy ultrasound:
- Face: Depending on the positioning of your baby, the technician may or may not be able to detect if your baby has a cleft lip. Rarely are they able to detect if there is a cleft of the palate.
- Brain: The technician will be assessing the fluid-filled spaces inside the brain and the shape of the cerebellum, which is in the back of the brain. He or she will also be able to identify if any cysts are in the choroid plexus, which is a tissue in the brain that produces cerebrospinal fluid. Fetal cysts may indicate an increased risk for a chromosome abnormality; however, the majority of these cysts disappear by the 28th week of pregnancy with no effect on the baby.
- Skull (shape, integrity, BPD and HC measurements)
- Neck (nuchal fold thickness)
- Spine: Your baby’s spine will be evaluated in the long view and in a cross section. The technician will be looking to make sure that the vertebrae are in alignment and that the skin covers the spine at the back.
- Heart (rate, rhythm, 4-chamber views, outflow tract): Congenital Heart Defects are one of the leading causes of birth defects and infant death. A prenatal diagnosis can prepare you and your medical team to provide your infant with the best medical care possible throughout your pregnancy and after birth.
- Thorax (shape, lungs, diaphragm)
- Abdomen (stomach, kidneys, liver, bladder, wall, umbilicus, cord, abdominal circumference AC)
- Limbs (femur, tibia, fibia, humerus, radius, ulna, hands, feet femur length FL)
- Genitals (gender, abnormality)
- Cervix (length and opening)
Based upon the results of the measurements, the gestational age of the baby will be predicted based upon the average size of other babies scanned during the 20th week of pregnancy. If any abnormalities are found, additional examinations are indicated. http://nationalwomenshealth.adhb.govt.nz/Portals/0/A%20to%20Z/T%20to%20Z/U/Ultrasound%20-%20What%20is%20a%20fetal%20anatomy%20scan.pdf
- Level II Scan: While technically the anatomy scan is a Level II scan, there are other reasons to come in for a Level II sonogram. During your anatomy sonogram, you will learn if another Level II scan is needed. Level II scans are reserved for higher-risk mothers, but may be used to rule you out of the high-risk category. Common indications for a Level 2 ultrasound include family history of birth defects, maternal medical problems associated with birth defects (poorly controlled diabetes, for example), exposure to medications associated with birth defects, a maternal age of 35 or older, abnormal serum screening results, and birth defects suspected on a Level 1 ultrasound. While there is no ultrasound that can detect 100 percent of serious birth defects, most birth defects that are undetected with a Level 2 ultrasound usually are clinically less significant (such as a small hole in the heart which commonly closes on its own after birth or an isolated cleft palate with intact upper lip which can be fixed surgically after birth without any long-term complications). A survey of your baby’s internal organs will be conducted, as well as
- The umbilical cord
- Amniotic fluid
- Location of the placenta
- Fetal heart rate
- Bpp Scan (Biophsyical Profile): This sonogram combines an ultrasound evaluation with a non-stress test (NST) and is intended to determine fetal health during the third trimester. This test is performed if there is a question about fetal health and well-being resulting from either an earlier examination, maternal/fetal symptoms, or if the pregnancy is considered high risk. There are two parts to the BPP, a Non-stress Test (NST) and an ultrasound evaluation. The NST involves attaching one belt to the mother’s abdomen to measure fetal heart rate, and another belt to measure contractions. Movement, heart rate and “reactivity” of heart rate to movement are measured for 20-30 minutes. The ultrasound portion may take up to an hour, and the technician will watch for a variety of signs that are important in measuring the health of your baby. Usually, five specific fetal attributes are studied and “scored” during the BPP:
|Breathing||1 breathing episode within 30 minutes||No breathing episodes within 30 minutes|
|Movement||2 or more movements within 30 minutes||less than 2 movements within 30 minutes|
|Muscle Tone||1 or more episodes of active extension/flexion of limbs, etc. (i.e. opening and closing a hand).||Slow extension/flexion of limbs, partially open fetal hand, etc|
|Heart Rate||2 or more episodes of reactive heart rate acceleration within 20 min||1 or more episodes of unreactive heart rate acceleration|
|Amniotic Fluid||1 or more adequate pockets of fluid||Either no pockets or inadequate pockets of fluid|
The total score will help decide the overall health and well-being of your baby and help your doctor or midwife determine if your baby should be delivered sooner than planned.
- NST Scan: The Fetal Non-Stress Test is a simple, non-invasive test performed in pregnancies over 28 weeks gestation. As mentioned above, The NST involves attaching a belt to the mother’s abdomen to measure fetal heart rate, and another belt to measure contractions. Movement, heart rate and “reactivity” of heart rate to movement are measured for 20-30 minutes. A NST may be performed if:
- You sense the baby is not moving as frequently as usual
- You are overdue
- There is any reason to suspect the placenta is not functioning adequately
- You are high risk for any other reason
The test can indicate if the baby is not receiving enough oxygen because of placental or umbilical cord problems; it can also indicate other types of fetal distress. The primary goal of the test is to measure the heart rate of the fetus in response to its own movements. Healthy babies will respond with an increased heart rate during times of movement, and the heart rate will decrease at rest. The concept behind a non-stress test is that adequate oxygen is required for fetal activity and heart rate to be within normal ranges. When oxygen levels are low, the fetus may not respond normally. Low oxygen levels can often be caused by problems with the placenta or umbilical cord.