Prenatal Care 3 Reasons Why a Fetal Ultrasound May Be Wrong By Robin Elise Weiss, PhD, MPH Robin Elise Weiss, PhD, MPH LinkedIn Twitter Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor. Learn about our editorial process Updated on June 14, 2021 Medically reviewed by Brian Levine, MD, MS, FACOG Medically reviewed by Brian Levine, MD, MS, FACOG Brian Levine, MD, MS, FACOG, is board-certified in obstetrics-gynecology, as well as reproductive endocrinology and infertility (REI). He is the director and founding partner of CCRM New York and was named a rising star by Super Doctors from 2017 to 2019. Learn about our Medical Review Board Print The Image Bank / Getty Images Table of Contents View All Table of Contents Incorrect Pregnancy Date Technician Error Obesity The use of ultrasound in pregnancy is fairly commonplace. It was originally designed to help monitor the status of complicated or high-risk pregnancies. Today, ultrasounds are considered a standard facet of prenatal care. While ultrasounds can provide doctors and midwives with valuable insights into how a pregnancy is progressing, there are times when the results may either be misleading or inaccurate. An Incorrect Pregnancy Date An ultrasound technician, known as a sonographer, will look for certain features during the different stages of a pregnancy to determine if things are proceeding as they should. If the technician is unable to find that feature, it may be the sign of a problem. Or not. For example, if a woman is seven weeks pregnant and the ultrasound does not reveal a fetal heartbeat, there may be a moment of panic but the explanation could actually be quite simple. It's possible, that the dating of the pregnancy is off, and you're not nearly as far along as you thought. In such case, the doctor or midwife may order another ultrasound in a week. In the end, the pregnancy could be just fine, and all that is really needed a simple recalibration of the date. Technician Error Ultrasound technology has been greatly simplified in the past decade but still requires skill to obtain an accurate result. While most technicians have the necessary training to perform an exam, some, quite simply, are better or more experienced than others. While there has been no actual research into this effect in obstetrics, a study into the use of ultrasound in an emergency setting showed that errors or missed diagnoses occurred in anywhere from eight to 10% of cases. Similar results were seen other techniques such as chest X-rays (where the "miss rate" was over 20%) and mammography (where the "miss rate" was as high as 75%). If there is ever any uncertainty about the competency of a sonographer, you should ask for the attending physician to be present during the exam. Obesity Being overweight can make it difficult—and, in some cases, impossible—for a technician to get a clear ultrasound image. This is especially concerning since obesity is associated with an increased risk of fetal birth defects (including heart and gastrointestinal abnormalities) and such pregnancy complications as pre-eclampsia and postpartum hemorrhage. Studies have shown that obesity (defined as a body mass index of over 30kg/m2) reduces the likelihood of an accurate reading by nearly 50% (37% versus 19%) compared to women of normal weight. To overcome this, sonographers will often perform a transvaginal ultrasound (a device inserted into the vagina) at 12 to 15 weeks of gestation. This is the period during which defects can more often be spotted. In all other cases, the technician should be experienced in knowing how to "work around" areas of excess fat when performing an external, abdominal ultrasound. Ultrasound Accuracy for Predicting Due Dates 2 Sources Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Pinto A, Pinto F, Faggian A, et al. Sources of error in emergency ultrasonography. Crit Ultrasound J. 2013;5 Suppl 1:S1. doi:10.1186/2036-7902-5-S1-S1 Paladini D. Sonography in obese and overweight pregnant women: clinical, medicolegal and technical issues. Ultrasound Obstet Gynecol. 2009;33(6):720-9. doi:10.1002/uog.6393 By Robin Elise Weiss, PhD, MPH Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor. See Our Editorial Process Meet Our Review Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit