Ultrasound in the First Trimester and Earlier: How to Keep It Safe

Abstract

1"Ultrasound is safe. Ultrasound is not X-rays. Our machines are FDA-approved." These are the statements most commonly made when initiating a conversation on safety of ultrasound. This is one of the reasons cited for its becoming an essential tool in medicine (together with its relatively low cost and immediate results availability). Diagnostic ultrasound (DUS) has been in use for over half a century in obstetrics and gynecology [1] and the benefits of this technology are multiple [2]. Most pregnant women have 2-3 ultrasound examinations (and many more in certain countries) during their pregnancies. In early pregnancy and before (i.e., in Artificial Reproductive Technologies [(ART]), these include serial scans of the developing follicles during ovulation induction [3] and in the earliest stages of gestation [4], first-trimester ultrasound for viability and/or aneuploidy screening (nuchal translucency, NT) and, more and more, early anatomy survey [5]. Such is the widespread enthusiasm and the generally accepted notion of safety that its use has spilled into the commercial world with mall stores offering non-medical ultrasound or "souvenir" scans. The record of safety of DUS is excellent: there are no epidemiological studies demonstrating harmful effects in human fetuses [6]. Most human epidemiological studies, however, published so far are based on information obtained with pre-1991/1992 machines. Around that time, the US Federal Drug Administration (FDA) allowed the acoustic output of ultrasound machines for fetal use to be increased from 94 to 720 mW/cm 2 , a factor of almost 8 [7,8]. Is there enough evidence to validate the use of ultrasound imaging in general and Doppler in particular in the first trimester [9] and could ultrasound have detrimental effects on the fetus in the first trimester, a time of maximal susceptibility to external factors? If there are clinical indications to perform these scans (and if there were none, there would be no raison-d'être for this book) safety must be guaranteed by educating the end-users on ways to limit the possible hazards of exposure of the follicles/ova and the fetus at early stages of gestation [2].

Is Excessive Prenatal Ultrasonography a Risk Factor for Autism? A Literature Review

“…The highest exposure intensity within the beam (i.e., spatial peak) is averaged over the time of exposure (i.e., temporal average) and is named the spatial peak temporal average. [6][7][8][9][10] After ultrasound manufacturers developed output display standard (ODS) biosafety measures by displaying their levels on the ultrasonic screens, the Food and Drug Agency (FDA) in 1992 deregulated the acoustic output levels of clinical ultrasound systems, which produced better images and therefore improved diagnosis for patients. Ultrasonic acoustic output levels, emitted by the transducer, for fetal, neonatal, and pediatric imaging were augmented from 94 mW/cm 2 in 1986 11 to 720 mW/cm 2 in 1992, 12 including the peak exposure through the mechanical index, which enhanced potential biophysical effects exerted on the embryo and fetus.…”

“…Ultrasonic acoustic output levels, emitted by the transducer, for fetal, neonatal, and pediatric imaging were augmented from 94 mW/cm 2 in 1986 11 to 720 mW/cm 2 in 1992, 12 including the peak exposure through the mechanical index, which enhanced potential biophysical effects exerted on the embryo and fetus. 4,6,10,13 The ODS is composed of two indices to alert the end-user of temperature rise and mechanical impact. The soft tissue thermal index depends on three factors: transducer opening i.e.…”

“…beam width, beam direction, and scanning mode. The ultrasonic beam can produce heat 6,7,10 and cause hyperthermia 6,[9][10][11] to an embryo/fetus. The mechanical or cavitation index occurs because of an intense beam forming bubbles in soft tissue; if severe, mechanical injury causes cavitation in tissues.…”

“…[67][68][69][70] Brightness modulation (B-mode) scanners, used in the mid-1990s, are the source of the prevalent safety verification of PUS. 10,65,79,81 The new devices such as pulsed Doppler, color flow, or scanners produce 10-to 15-fold higher acoustic outputs than those of the earlier 1990s scanners;…”

“…[86][87][88][89] The current clinical practice is to scan all pregnant women who have low-or high-risk pregnancies at every prenatal clinic visit, which may amount to 10 scans per pregnancy. 10,76,77 Souvenir or keepsake fetal ultrasounds has expanded into a major industry and are conducted by nonmedical personnel. [90][91][92][93] The FDA 94…”