Ultrasound in Pregnancy
by Audrey Mendenhall , RT,RDMS,RDCS
Sound Health Imaging
It has been approximately 3 decades since the introduction of ultrasound to evaluate pregnancies. Initially, this type of imaging was quite limited in the information that it provided. The resolution of the ultrasound image in those early days only answered some basic questions regarding the pregnancy: Is there a pregnancy? Is it viable? What is the gestational age? Are there twins? Will the location of the placenta interfere with delivery?
Ultrasound technology has improved dramatically over the past thirty years with major advances in the amount and quality of information provided during an obstetrical ultrasound exam. Correspondingly, it’s use by medical practitioners has escalated. In some countries, as many as 90 to 100% of pregnant women will have at least one ultrasound during their pregnancy. In Scotland the average number of scans per pregnancy is 2.8. In Germany, three ultrasound scans (weeks 9-12, 19-22 and 29-32) are routinely performed during pregnancy. Here in the United States one ultrasound is considered the standard of care, and many insurance companies allow for two scans in a routine low-risk pregnancy.
With the introduction of endovaginal transducers, the resolution of first trimester imaging has greatly improved. In the first trimester, ultrasound exams are done to demonstrate viability of the pregnancy. A heartbeat can be detected at approximately 6 weeks menstrual age. This is also the most accurate time to date the pregnancy. A new genetic screen is now available called an Ultrascreen that is employed during weeks 11-14 of pregnancy. This test utilizes ultrasound in conjunction with a maternal blood sample and provides a risk assessment of the likelihood of the baby having a chromosomal abnormality. It has a detection rate of 91-95% in the hands of an experienced sonographer.
At approximately the half-way point in pregnancy, most women will undergo a second-trimester obstetrical ultrasound exam. This 18-22 week scan provides a wealth of information about the pregnancy. This is still a good time to date a pregnancy so measurements are done of the fetal head, abdomen and femur. The placenta location is noted as a placenta positioned over the cervix (placenta previa) is a life threatening condition for both mother and baby. The cervical length is measured. A shortened cervix during the second trimester may indicate pre-term labor.
The ability to visualize fetal anatomy during second-trimester ultrasound exams has improved dramatically thanks to major technological advances. Many aspects of the brain are evaluated in the fetal head. The fetal face, spine, arms, legs, hands, feet, stomach, kidneys, bladder and umbilical cord are imaged for proper development. With the latest high resolution ultrasound equipment, even subtle abnormalities such as cleft-lip or club- foot are apparent. In the early days of ultrasound, only fetal heart motion could be detected. Now virtually all major congenital heart defects are detected. Not only can the heart motion be seen and heard, but all 4 chambers of the heart are documented. It is now also possible to visualize the aorta arising from the left ventricle and the pulmonary artery from the right. The returning veins into the right and left atria are readily visualized as well as the aortic arch and its branches. Last but not least, this is the time when the fetal gender is easily determined for the parents wanting to know the sex of their baby!
Third trimester ultrasound exams are usually reserved for pregnancies where there is some type of concern. Either the healthcare provider questions the growth or well being of the baby or the mother develops a condition such as gestational diabetes or elevated blood pressure. Near delivery, an ultrasound may also be done to make sure the baby is not in breech position.
Ultrasound in pregnancy has become an invaluable tool to those providing obstetrical care. It also provides the pregnant woman with the opportunity to bond with her unborn baby. The ultrasound exam has a positive impact on the expectant mother’s feelings. Studies have shown that following an ultrasound, pregnant mothers will make positive lifestyle changes such as quitting smoking or eating more nutritiously.
Undoubtedly, the early pioneers of obstetrical ultrasound could not have foreseen the amazing technological advances now on the forefront of obstetrical ultrasound. The recent introduction of 3D/4D imaging is the latest ultrasound technology being employed. The future will undoubtedly unfold even greater advances in our ability to view life in the womb.
Ultrasound Timeline in Pregnancy
Early First Trimester: In the first trimester, ultrasound exams are done to demonstrate the viability of the pregnancy. A heartbeat can be detected at about 6 weeks menstrual age. This is also the most accurate time to date the pregnancy.
11-13 Weeks: A new genetic screen is now available called an Ultrascren that is used at 11 to 13 weeks to assess the likelihood of any chromosomal abnormalities. In the hands of an experienced sonographer, its detection rate is 91-95%.
19-20 Weeks: Most women will have a scan at the halfway point of their pregnancies, which is an ideal time to learn a wealth of information about the pregnancy. To date the pregnancy, measurements are taken of the fetal head, abdomen and femur.
The placenta location is noted, because a placenta positioned over the cervix (placenta previa) is a life-threatening condition for both mother and baby. The cervical length is measured, indicating the probability of pre-term labor.
Technological advancement has greatly improved the visibility of fetal anatomy during the second trimester. The fetal brain is evaluated for proper development, as well as the face, spine, arms, legs, hands, feet, stomach, kidney, bladder and umbilical cord. With the latest high-resolution equipment, even subtle abnormalities, such as cleft lip or club foot, ar apparent.
Virtually all congenital heart defects are detected now, with the heartbeat heard and all four chambers of the heart seen. It is now also possible to see the aorta rising from the left ventricle and the pulmonary artery from the right, as well as the returning veins into the right and left aorta with its branches.
Finally, this is the time when fetal gender is easily determined for parents who want to know.
26-30 Weeks: This is the optimal time during pregnancy to get a 3D/4D ultrasound of your baby. Plenty of fluid makes for good viewing, and the baby is big enough to show his or her unique physical features. The newest machines provide not only photos, but DVD’s of your baby living and moving in the womb.
Third Trimester: Ultrasound exams at this stage of pregnancy are usually reserved for those where there is a concern. The healthcare provider questions the growth or well-being of the baby, or the development of a condition in the mother, such as gestational diabetes or elevated blood pressure.