Transvaginal Cervical Length Assessment
Preterm birth (delivery of the baby before 37 weeks into the pregnancy) occurs in about 1 in 7 pregnancies. The rate is much higher with twins, where more than 50 percent of women deliver before 36 weeks, and even higher with triplets, where more than 50 percent of women deliver before 33 weeks.
Assessment of the cervical length by ultrasound can be very helpful in assessing women for preterm delivery risk. For example, all women with prior cervical surgery may be at increased risk to have weakness of the cervix due to the surgery, which can result in very premature delivery. We can assess for this with transvaginal cervical length assessment.
A woman who has had a prior premature baby is typically seen every couple of weeks, starting several weeks before the preterm baby was born, to make sure that the cervical length is staying normal. A drop in cervical length, or an abnormal appearance to the internal contours of the cervix, can be an early warning system for threatened preterm labor, and, oftentimes, we can recommend interventions to reduce the chance that the baby delivers early.
Umbilical Cord Doppler Velocity Studies
Research has shown that the pattern of blood flow within the umbilical cord can be an important predictor of babies who are heading for growth problems, or for babies with growth problems who are getting sick in utero. Situations in which umbilical cord Doppler studies may be recommended include women who have had a prior baby with growth problems, who have a baby in the current pregnancy who is falling behind the normal growth curve, or who have conditions, such as high blood pressure, asthma, or heart disease, which place the baby at risk for growth difficulties.
Middle Cerebral Artery Doppler Studies
Some pregnancies are at risk for the baby developing anemia before birth. The most common reason for this is women who have blood group isoimmunization.
The only direct way to know that the baby is or is not anemic is by means of placing a needle into the umbilical cord to obtain a blood sample and measure the baby’s blood count. This carries a significant risk to the pregnancy, but is very, very accurate. Studies have shown that sonography can be used as an excellent screening test for fetal anemia. The concept is that the baby with anemia will have a lower viscosity of the blood than a baby with a normal blood count. The lower viscosity blood flows more quickly through baby’s blood vessels, in much the same way as water flows through a funnel faster than oil.
Years ago, researchers measured the blood flow in many different arteries of the baby, including vessels within the heart, spleen, or within the brain. It turns out that the middle cerebral artery is a very easy place to measure baby’s blood flow, and gives reproducible results that correlate very well with a baby who is anemic. A normal middle cerebral artery blood flow study is typically repeated at intervals of one or two weeks, since a baby who is not anemic today might become anemic within a couple of weeks.
Ultrasound can also be used as a means of ongoing assessment of baby’s good health in utero. There are certain conditions that place the pregnancy at increased risk for stillbirth. These include maternal age 40 or older, twin gestation, and maternal health conditions, including high blood pressure and diabetes. The risk of stillbirth in the general obstetric population is about 1 in 200 pregnancies. This risk is reduced by having all moms do daily “kick counts” from 26 weeks in the pregnancy onward.
For women at increased risk, a twice-a-week assessment of the baby by means of an ultrasound scan to check baby’s activity pattern and fluid volume, as well as fetal monitoring, is often recommended. The combination of a normal fetal heart rate tracing and normal ultrasound evaluation of activity and fluid volume places the pregnancy at very low risk for stillbirth. In fact, this type of surveillance can reduce the chance for a high-risk pregnancy to result in stillbirth to a risk figure on par with that of low-risk pregnancies.
Mechanical PR Interval
An amazing application of ultrasound technology is that it can be used to predict, and in concert with medical treatment, oftentimes prevent the development of conduction system abnormalities within the baby’s heart. Women with Sjögren antibodies (which can occur in systemic lupus and in Sjögren syndrome) are at increased risk to have babies with congenital heart block. By making a very precise measurement of conduction within the baby’s heart — the mechanical PR interval — we can detect subtle abnormalities of the conducting system of the heart, and then treat with medications to prevent, in many cases, progression to complete heart block, a very serious problem for the baby.