What are ultrasounds?
Ultrasounds are sound waves used in medicine to image various internal organs and have been used for the past 30 years. So far, there is no evidence that ultrasounds can cause harm to the fetus.
Why should we have an ultrasound during pregnancy?
How many ultrasounds are needed?
Most babies are healthy; however, about 1–2 babies are born with a serious abnormality or intellectual disability. With ultrasound, we can diagnose approximately 90% of severe abnormalities. Ultrasound also provides information about fetal growth and the position of the placenta.
The 11–14 week ultrasound (Nuchal translucency, nasal bone, PAPP-A). One of the most common causes of intellectual disability is Down syndrome. Babies with Down syndrome always have some degree of intellectual disability and often have heart problems. Any woman can give birth to a baby with Down syndrome, but the likelihood increases as maternal age increases.
The only way to be certain that the fetus does not have Down syndrome is to perform a diagnostic test (amniocentesis or chorionic villus sampling), in which genetic material from the amniotic fluid (amniocentesis) or placenta (chorionic villus sampling) is examined. This material is identical to the fetus’s genetic material (chromosomes). However, these procedures carry a small risk of miscarriage (0.5–1%).
For this reason, the decision to undergo such a procedure is best based on a test that estimates the probability that the fetus has Down syndrome. This test is the 11–14 week ultrasound, focusing on the presence of the nasal bone (the fetal nasal bone).
When these findings are combined with the measurement of two maternal blood hormones, we can predict at least 9 out of 10 babies with Down syndrome (sensitivity 95%).
ALPHA-FETOPROTEIN TEST, TRIPLE TEST: the A test
This test is performed between the 15th and 18th weeks of pregnancy to measure the levels of alpha-fetoprotein (AFP) in your blood. This protein is produced by your baby and passes into your bloodstream during pregnancy. High levels of this protein are associated with spina bifida, and you will therefore be advised to have an ultrasound and an amniocentesis to confirm the diagnosis.
The triple test is a term used for a blood test performed on the mother to detect Down syndrome. It combines the AFP result (which also provides information about the risk of spina bifida) with the measurement of other blood chemicals to estimate the risk of giving birth to a baby with Down syndrome.
The triple test is not useful in the case of twins or multiple pregnancy. Some maternity clinics provide results as “low risk/screen negative” or “high risk/screen positive.” A negative result means that the risk of having a baby with Down syndrome is low. A positive result means that you have a high risk of giving birth to a baby with Down syndrome. For example, any level above 1:250 is considered “high risk.” This is usually the cutoff point. However, a risk of 1:100 still means a 1% chance of the baby having Down syndrome and a 99% chance of being born healthy. You will be advised to undergo an amniocentesis to obtain a definitive diagnosis. You may compare this risk with your age-related risk (approximately 1:700 at age 30) or the risk of miscarriage from amniocentesis (about 1:100).
Amniocentesis / Chorionic Villus Sampling (CVS)
Amniocentesis (collection of amniotic fluid) and chorionic villus sampling (collection of a biopsy from the placenta) are invasive methods used to examine the chromosomes of the fetus. Chorionic villus sampling is performed from the 11th week of pregnancy. Under ultrasound guidance, a thin needle is inserted into the placenta to obtain tissue (chorionic villi).
Similarly, amniocentesis is performed from the 16th week. Under ultrasound guidance, a thin needle is inserted into the amniotic sac to collect amniotic fluid. With both methods, the number and integrity of the chromosomes are examined, allowing major abnormalities — such as Down syndrome — to be ruled out.
However, this testing cannot exclude all abnormalities, and a normal result does not guarantee the birth of a healthy baby. Both amniocentesis and chorionic villus sampling carry a small risk of miscarriage (0.5–1%).
The 21–24 week ultrasound and the 4D ultrasound
(Second-trimester anatomy scan)
The second-trimester anatomy scan is performed between the 21st and 24th week of pregnancy and includes a series of measurements to assess fetal growth, evaluate the placenta, estimate the amniotic fluid, and conduct a detailed examination of the fetal organs for congenital abnormalities.
The scan evaluates the skull, brain, face, spine, chest, heart, abdomen, kidneys, bladder, arms, and legs. With this detailed ultrasound, approximately 70% of severe abnormalities, about 45% of milder abnormalities, and overall around 55% of congenital anomalies can be detected. Some abnormalities develop during pregnancy or may appear late in pregnancy or after birth. Unfortunately, no ultrasound — no matter how detailed or comprehensive — can exclude all abnormalities or guarantee the birth of a completely healthy child.
The fetus is also examined for markers (signs) of chromosomal abnormalities. About half of fetuses with Down syndrome have one or more markers, although most fetuses with markers are healthy. The results of the 11–14 week scan are considered together with the first-trimester combined test and the second-trimester anatomy scan when calculating the final probability of Down syndrome. Using color Doppler ultrasound, the blood flow in the uterine arteries is assessed. If the resistance in the uterine arteries is increased, the likelihood of the mother developing preeclampsia or the fetus having low birth weight is higher.
About 1 in 4 women with increased resistance will experience such complications, while the remaining pregnancies will progress normally. If increased resistance is identified in the anatomy scan, regular monitoring of the mother's blood pressure and monthly fetal ultrasound examinations are recommended.
Finally, the length of the cervix can be measured. The cervix is the lower part of the uterus that opens (dilates) during labor. Its measurement is reliably performed via transvaginal ultrasound. If the cervix has significantly shortened (less than 15 mm), the risk of preterm birth increases. In such cases, your doctor will suggest appropriate treatment to reduce the likelihood of this serious complication. Recent studies have shown that such measures can reduce the incidence of very preterm birth by up to 40%.
The 4D ultrasound provides a three-dimensional, live (real-time) image of your baby.
Growth ultrasound and Doppler
The growth ultrasound is performed from 24 weeks until the end of pregnancy, usually every four weeks. It assesses the fetus’s growth, its weight, the quality of the amniotic fluid, and the position of the placenta. The Doppler examination evaluates blood flow in the vessels of the fetus and the placenta (usually the umbilical artery and the middle cerebral artery). It provides information about placental function and the condition of the fetus. These findings are particularly important for growth-restricted babies and help us determine whether a small-for-gestational-age fetus is receiving enough oxygen and nutrients from the placenta. When blood flow in these vessels is not normal, more detailed and frequent monitoring is required.
- Obstetrics
- High-Risk Pregnancy
- Multiple Pregnancy
- General Gynecology
- Gynecological Endocrinology
- Infertility
- In Vitro Fertilization (IVF)
- Endometriosis and laser treatment
- Diagnostic and Operative Hysteroscopy
- Diagnostic and Operative Hysteroscopy
- Endometrial Ablation
- Colposcopy
- Urogynecology
- Laparoscopic Pelvic Floor Reconstruction
- TVT
- TOT
- Vaginal Reconstruction
- Gynecologic Oncology
- Ultrasound
