by Elizabeth MacDonald
This post made possible by the generous support of My Baby’s Heartbeat Bear
This article originally published on mybabysheartbeatbear.com on November 10, 2015.
In the article “Pregnancy Sonograms and What You Will Learn, Part 1” we talked about the different kinds of ultrasounds and their purpose, ending with more detail about the general anatomy scan common around 20 weeks of pregnancy. In this article, we’re taking a deeper look at the types of scans done prenatally and the reasons why your healthcare provider may recommend them as a diagnostic tool. These scans can provide valuable information on the health of your baby when necessary.
Your doctor or midwife may recommend one or more of the following sonograms throughout your pregnancy, for various reasons. You may not know when you conceived or may have suffered previous miscarriages. You may be over the age of 35 and your doctor requires extra screening. There may be genetic reasons for extra scans, or a low lying placenta that could threaten a vaginal delivery. Your little fetus may stubbornly decide to lay transverse and a late sonogram is needed to see position. There are numerous reasons to receive sonograms other than the 20 week anatomy scan.
- 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 an 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 visible 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 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 gestationthe baby and its heart beat can be detected relatively easily with trans-abdominal and trans-vaginal examination.
- This is presuming that the pregnancy is actually at this stage of development.
- Sometimes a trans-vaginal examination shows that your pregnancy is less advanced than expected.
- 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, Edward’s 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.
- 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
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.
- Bpp Scan (Biophysical 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:
- 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.
Many pregnancies progress just fine without ever having an ultrasound and health care providers use a wide array of skills and tests to ensure the safety and health of both the mother and the baby through pregnancy and birth. Having any of these scans done isn’t immediately an indication of a problem, it is just an opportunity to check. It is a gift to hear your baby’s heartbeat and see them developing, one to treasure. While it can be exciting to hear your baby’s heartbeat and to see them on the screen, the purpose of ultrasounds is to be an important tool in your prenatal care, not an entertainment experience. They may provide some answers to questions and concerns, reveal a potential problem or that everything is developing normally, and provide reassurance. Be sure you are using a reputable ultrasound technician to perform your scans, your healthcare provider should refer you to one they trust and use regularly if it is out of office. If you feel that a scan is unnecessary and are unsure you want to go through with it, be sure to speak with your healthcare provider about your concerns to better understand the purpose of the scan. If at any point there is something you don’t understand, speak up and let your healthcare provider know you have questions.