This ultrasound is incredibly detailed and is designed to assess all appreciable fetal structures at 18-20 weeks gestation. At this point in the pregnancy, details of the fetal organ systems (skeletal, cardiovascular, genitourinary, gastrointestinal, etc) can be imaged by ultrasound. Many structural or genetic concerns can be identified at this stage in the pregnancy. There are some structures (ex. the fetal brain), however, which are in constant development and cannot be fully assessed in one visit and may need to be imaged over a series of ultrasounds, especially if there is a concerning finding.
If a patient has a risk factor for a chromosomal difference, aneuploidy markers (or “soft signs”) can be assessed by ultrasound. These “markers” are not abnormalities but rather raise concern for a possible genetic difference. If no markers are seen, then the patient’s risk can be reduced. Indications for aneuploidy screening by ultrasound include an increased risk of a genetic difference but are not limited to: maternal age > 35, abnormal maternal serum screening or abnormal NIPT/ cell free DNA screening, and increased nuchal thickness > 3-3.5 mm in the first trimester.
3D/4D surface rendering of the fetus can better demonstrate abnormalities previously detected with 2D sonography, especially facial, skeletal, and central nervous system abnormalities. Since ultrasound imaging requires skill to interpret, not all patients “connect” with the 2D image of the fetal face. If possible, we can always try to obtain a 3D/4D image for the patient so the baby’s face can be “seen” more clearly to the patient. 3D/4D imaging requires adequate space between the fetus and the uterine wall, amniotic fluid, and the fetal position “face up” and is therefore is not guaranteed.
3D/4D imaging is available and performed as a courtesy to our patients when the fetus is in a position that allows for the images to be obtained. Unfortunately, 3D/4D ultrasound is extremely position dependent, so it is not always possible to obtain these images for entertainment purposes. In the event we are able to, there is no additional charge for this complimentary service.
Unfortunately, even with the best technology and skill, not all fetal structural abnormalities or conditions can be diagnosed antenatally. As the fetus grows and develops, structural differences may become more readily apparent and sometimes they only become apparent after birth.
A fetal echocardiogram may be performed to evaluate the structure and function of the fetal heart. Family history of congenital heart disease, obesity, abnormal screening tests, and IVF are just a few of the clinical indications or reasons for a fetal echo. We are able to evaluate the fetal heart for any problems with the heart walls, valves, vessels leading to and from the heart, and the heart’s function overall or pumping strength. This study includes assessment of fetal cardiac structure and function. Doppler studies are also performed to visualize blood flow and turbulence.
Transvaginal ultrasound (performed through the vagina) is safe during pregnancy for both mother and baby. There are no known risk factors associated with transvaginal ultrasound. This method is commonly used to evaluate fetal anatomy in the first trimester, cervical length, and placental location.
Transvaginal ultrasound may be offered for a number of reasons. The most common is to visualize and measure the maternal cervix. The cervix should be long and closed early in the pregnancy and this finding reduces the chance of a preterm delivery. Other times, transvaginal ultrasound may be indicated to assess the fetal structure, since early in the pregnancy the fetus can be too small to adequately visualize through the maternal abdomen. Or later in pregnancy, fetal structures in the lower uterus can sometimes be best imaged by transvaginal scanning; for example, if the fetal head is down, this is an excellent way to image intracranial anatomy and brain structure, or if the fetal bottom is down, then imaging of the lower spine and kidneys is enhanced. Occasionally, transvaginal ultrasound is used due to limitations experienced during the transabdominal ultrasound including fetal position, maternal body habitus, and overlying bowel gas that obscures the view of the sonographer.
If your doctor has a concern about the placental location and is worried the placenta may be blocking delivery (complete placenta previa), transvaginal ultrasound is the best way to accurately assess the location of the placenta in relation to the cervix.
Transvaginal ultrasound measurement of cervical length is useful for supporting or excluding the diagnosis of cervical insufficiency or preterm labor when the diagnosis is unclear. The maternal cervix is measured by ultrasound as a screening tool, since a short cervix is often detected on ultrasound examination before it can be appreciated on physical examination.
All patients have a cervical length measurement at their anatomical survey, most of the time by transabdominal imaging. If there are other risk factors for preterm birth, if the cervix cannot be adequately imaged, or the cervix appears short on transabdominal scanning, then a transvaginal ultrasound will be done for a more detailed assessment.
“Cervical shortening” is one of the earliest signs of preterm labor and can precede labor by several weeks. The cause is often unclear. A short cervical length before 24 weeks can be predictive of preterm birth and is most predictive in women with early and significant cervical shortening.
A long cervix (≥30 mm) before 34 weeks of gestation has a high negative predictive value for preterm birth, meaning preterm birth is unlikely to occur.
Doppler ultrasound is used for assessment of fetal circulation and wellbeing. It can also be used to assess placental resistance in cases of poor fetal growth.
The fetal biophysical profile (BPP) is a noninvasive, ultrasound test for evaluating the fetus for signs of compromise. Ultrasound is used to assess four discrete biophysical parameters: fetal movement, fetal tone, fetal breathing motion, and amniotic fluid volume. The fetus has 30 minutes to perform these activities and points are assigned for each activity appreciated. The most points a fetus can obtain with ultrasound is 8. A score of 8 is reassuring. A score of 6 may require a second BPP within 12 to 24 hours. A score of 4 or less may mean you need additional tests or that your baby might need to be delivered. Sometimes a non-stress test will be added for additional assessment.
A number of fetal measurements are taken by ultrasound and placed in a formula to create an estimated fetal weight (EFW). The main fetal measurements taken for a growth scan include: head, abdomen, femur, and the humerus. The EFW can be used to help determine whether the fetus is average, larger or smaller in size for its gestational age. These measurements are most precise early in pregnancy with up to 15% error later in gestation due to difficulties with late pregnancy imaging and acoustic shadowing. If a fetus is at less than the 10th percentile for its gestational age, you may need further fetal assessment by ultrasound and wellbeing studies.
If you have had prior uterine surgeries (myomectomy, cesarean section, operative hysteroscopy, dilation and curettage) it is possible that the placenta can invade deeper into the uterine muscle than normal (instead of just the inner uterine surface or mucosa). Fortunately, this is a relatively rare occurrence. It would be important to let your physician know if you had any prior uterine procedures.
If you have a chronic medical condition (hypertension, obesity, hypothyroidism, diabetes, autoimmune condition) or have developed a pregnancy related complication (preeclampisa, vaginal bleeding), your obstetrician may recommend you see a MFM physician for consultation and pregnancy care planning.
If your obstetric physician finds a fetal concern (structural, screening blood test, or diminished fetal growth) then you may be referred to a MFM physician for a detailed ultrasound assessment.
Chorionic Villus Sampling (CVS) and amniocentesis are diagnostic tests you may be offered to check if your baby has a genetic or chromosomal condition. These tests are not a screening tool but rather give complete and final information regarding the genetic makeup of the fetus.
A CVS is typically performed within the 10th to 13th week of pregnancy, earlier than amniocentesis. This procedure involves testing a small sample of cells from the placenta, which is the organ that links the mother's blood supply with her fetus and contains fetal genetic information. The sample can be easily taken through the cervix (trans-cervical) or the abdomen (transabdominal) without entering the amniotic sac or disrupting the membrane or the fetus.
Amniocentesis is a procedure that is performed after the 15th week of pregnancy in order to determine if the fetus has a genetic/chromosomal difference or an open neural tube defect (ONTD
If you have undergone a prenatal screening test that has indicated a heightened concern about your pregnancy, you may decide you would like to have a CVS or amniocentesis to alleviate anxiety and to understand the baby’s condition more clearly or to find relief that “everything is ok”.
This is a non-ultrasound test for fetal health. The fetal heart rate is detected by a Doppler placed on the maternal abdomen with an elastic belt and the fetal heart rate is “traced” on a grid paper over time. The fetus is usually given 20 minutes on the monitor and the goal (after 32 weeks) is to find heart rate accelerations (15 bpm over baseline) that last over 15 seconds. This is generally a sign of good fetal health and the absence of fetal distress or poor oxygenation.
Prenatal screening tests can identify if your baby is higher risk for a structural or genetic concern. These tests are not invasive (therefore do not place your pregnancy at risk) and can include a combination of a blood test (prenatal cell-free DNA screening) and a detailed ultrasound (looking for genetic markers). However, prenatal screening tests are limited and do not provide a definitive, clear diagnosis. If a screening result points to an increased risk for a genetic disorder or structural difference, you may decide you would like a definitive test to confirm the diagnosis.
First trimester ultrasound for fetal structure
This ultrasound is done early in the pregnancy at 11-13 6/7 weeks to assess for major or serious fetal structural abnormalities. Many patients would like to know if their pregnancy is “healthy” as soon as possible, especially before making announcements to friends, family, or their employer. While this ultrasound cannot always detect subtle differences in fetal structure, it is able to detect major issues which may be lethal or have adverse effects on the mother’s health.
The detailed obstetric ultrasound examination in the late first trimester is an indication- driven examination for women at increased risk for fetal or placental abnormalities. Approximately 50% of major anomalies are detected in this gestational age window.
First trimester ultrasound anatomical survey does not replace a second trimester detailed exam. All structures imaged will need to be reevaluated during future studies.
These early anatomical surveys are helpful to assess global issues or obvious problems but if a structure is felt to be "normal" at this gestational age, it will need more detailed evaluation later and new findings may appear.
The first trimester ultrasound is done to rule out major lethal anomalies as early as possible in the gestation.