Ultrasound Monitoring in First Trimester of Pregnancy
Abstract: Why the Ultrasound Monitoring is Extremely Essential in the First Trimester of Pregnancy?
The article was designed as a retrospective overview of the main determinants of the early ultrasound monitoring with special emphasis given to the basic indicators, complexities and risks which are in close correlation with the early intrauterine pregnancy diagnosis, particularly, the occurrence of intrauterine or extrauterine Gestational Sacs prior to a visible embryo could be detected inside. Complications, interconnected with early pregnancy ultrasound management were inclusively represented. The perspectives of the further analysis, concerning ultrasound dimension, were outlined.
Introduction
The availability of high–resolution Transvaginal Ultrasound enables the visualization of very early pregnancies, particularly, the occurrence of intrauterine or extrauterine Gestational Sacs prior to a visible embryo could be detected inside. In other words, accuracy of Transvaginal Sonography enables to have an intrauterine sac visible when an intrauterine pregnancy is present, consequently, the diagnosis of intrauterine pregnancy can be established in very early embryo gestation, but the absolute determination of the further embryo viability, development into fetus and successful pregnancy outcome as a birth of a normal neonate cannot be predicted on the basis of early pregnancy diagnosis, therefore, early pregnancy necessitates periodical ultrasound monitoring with inclusive interpretation and documentation in the pregnancies’ histories of the received results.
1. Is it possible to predict the embryo viability in the early intrauterine pregnancy based on early ultrasound conclusions? What should be done if the early ultrasound scan’s conclusive interpretations indicate the diagnosis of uncertain pregnancy viability? Modalities of uncertain pregnancy viability: proposed clinically implemented model for prediction of the viability of early intrauterine pregnancy when no embryo is visible on ultrasound.
The strongest association with the first trimester of embryo life is excessive vulnerability, as the commonest early pregnancy complication of spontaneous miscarriage. At present, Transvaginal Ultrasound scanning enables the visualization of very early pregnancies prior to there being a visible embryo. Consequently, with a reasonable degree of accuracy, longitudinal assessment of early pregnancy development can be made in terms of viability and growth. Despite the significant advancements in Transvaginal three–dimensional (3D) Ultrasound techniques and tremendous improvements in the first trimester embryo’s visualization, it should be noted that Transvaginal Ultrasound scanning disables the visualization of absolute criteria, which can indicate embryo viability, therefore the clinicians should focus almost exclusively on identifying the determinants of early pregnancy signs and symptoms, what are supposed to be an imperative in predicting the further embryo viability and are thought to be essential for preventing early embryo loss and for establishing the accurate diagnosis of extrauterine pregnancy or failed intrauterine pregnancy.
When a small Gestational Sac with no visible embryo inside [embryo cardiac activity has never been previously identified] is seen at an early pregnancy ultrasound scan, the clinician cannot accurately distinguish a viable from a non–viable pregnancy. Detection of a small, apparently empty Gestational Sac on ultrasound scan is not enough to give the conclusive diagnosis of further pregnancy progress: for instance, 4th–5th week of Gestational Age is too early to identify an embryo, or it may be a failing pregnancy destined to miscarry.
In absence of a relevant diagnostic gold standard for making the prognosis of further embryo viability, the only inclusion criteria for diagnosis of intrauterine pregnancy are conception, Gestational Sac of <20 mm mean diameter (the Gestational Sac should be measured from the inner edges of trophoblast in three orthogonal planes), no visible embryo on Transvaginal Ultrasound scan and outcome data regarding the probability of embryo viability [Lautmann et al., 2011].
The diagnosis of an Intrauterine Pregnancy (IUP) is usually considered definitive only when a yolk sac or embryo is identified within an intrauterine Gestational Sac [Farquharson et al., 2005]. Unless the woman has a certain nonviable intrauterine gestation including an empty sac (an embryonic gestation), early fetal demise (embryonic demise), or retained trophoblast tissue (incomplete miscarriage), – all these adverse outcomes would be classified as miscarriage or Spontaneous Abortion (SAB) [Farquharson et al., 2005]. Bahceci and Ulug (2005) outlined additional modalities for clinical pregnancy diagnosis’ determination: ‘pregnancy is diagnosed as the presence of an intrauterine implanted embryo, defined as an intrauterine Gestational Sac as determined by Transvaginal Ultrasonogram following ICSI and Embryo Transfer. A Gestational Sac is defined by the presence of an intrauterine hypo–echoic area of ≥8 mm and covered by a double echogenic rim with a visible yolk sac (diameter >2 mm)’ [Bahceci and Ulug, 2005]. The other studies have implicated that the definition of Intrauterine Pregnancy (IUP) includes an identified intrauterine Gestational Sac regardless of the findings of a yolk sac or embryo, and regardless of viability.
Lautmann et al. (2011) defined 4th–5th week of embryo’s [embryo must be present into uterus] Gestational Age as ‘Early Intrauterine Pregnancies’ (EIUPs) [Lautmann et al., 2011]. Alternative term with more transparent interpretation used in some Early Pregnancy Units (EPUs) is ‘intrauterine pregnancy of uncertain viability’ [Royal College of Obstetricians and Gynaecologists, 2006]. It is noteworthy to mention that ‘uncertain viability’ is the condition, when it is possible to detect by the ultrasound scan the intrauterine sac (<20mm mean diameter) with no obvious yolk sac or fetus; or fetal echo <6mm crown–rump length with no obvious fetal heart activity [Lautmann et al., 2011].
It is highly recommended that a systematic re–evaluation of the current intrauterine pregnancy’s progress should be performed to confirm or refute viability, particularly, a repeat ultrasound scan should be done at a minimal interval of 1 week [Royal College of Obstetricians and Gynaecologists, 2006]. By this time, further growth in the intrauterine Gestational Sac or appearance of contents such as a yolk sac or embryo should have occurred if the pregnancy is ongoing.
Complications, interconnected with uncertain pregnancy viability are inclusively represented by the obstetric adverse complications’ rates and by the early pregnancy loss rates, which are currently high. In this respect, the scientific group under the management of the leading expert Lautmann K. established ‘a gold consensus’ of modalities, which can be used to predict the viability of early intrauterine pregnancies, when no embryo is visible on ultrasound, which is the combination of three parameters: maternal age, measurement of Gestational Sac Diameter (GSD) and measurement of progesterone levels, represent the estimation of the probability of a viable pregnancy [Lautmann et al., 2011].
The consensus was established in almost all controversies including the basic recommendations noted for implementation into clinical practice in the conclusion, particularly, it was revealed that the discrepancy between Gestational Age and Gestational Sac Diameter (GSD) could reflect early severe embryonic intrauterine growth restriction and was a predictor of subsequent miscarriage [Lautmann et al., 2011].
Additionally, it was established that an irregular Gestational Sac or abnormal placenta, an empty amniotic sac or a collapsed or dilated yolk sac are all markers of a failing pregnancy. However, with small Gestational Sacs <20 mm diameter, these markers cannot be taken in isolation to definitively diagnose miscarriage and the presence and absence of a yolk sac had no predictive value for pregnancy viability. The number of standard deviations from the expected mean Gestational Sac Diameter (GSD) has been suggested as the most powerful independent predictor of pregnancy failure [Lautmann et al., 2011].
2. Why the Ultrasound Monitoring is Extremely Essential in the First Trimester of Pregnancy? Ultrasound management of early pregnancy: four basic fetal biometric measurements, visualized by the ultrasound scan, which are used by the clinicians for concluding the embryo viability or intrauterine death.
Multivariate paradigm of the improved diagnostic accuracy in differentiation of intrauterine gestations from extrauterine gestations has vividly outlined the establishment of two integrative modalities: the implementation of advanced ultrasound technologies in pregnancy guidance and establishment of exclusion–inclusion criteria for distinguishing a normal intrauterine pregnancy from an extrauterine pregnancy and failed intrauterine pregnancy, based on ultrasound monitoring and accurate interpretation of received data, which can be validated systematically and periodically.
Previously, approximately two decades ago, the clinician’s ability to confirm the embryo’s viability or the embryo’s non–viability using the ultrasound scan, was significantly related to Gestational Age. Currently, the spectrum of advanced technologies, particularly, the introduction of virtual reality enables the clinicians to implement this technique widely into the ultrasound pregnancy monitoring by using all three dimensions in a high–quality three–dimensional ultrasound imaging, what would significantly reduce the number of inconclusive ultrasound scans (when the accuracy of diagnosis cannot be established).
The exclusiveness of ultrasound pregnancy management consists in accurate fetal growth visualization with special emphasis on early identification of growth abnormalities. Furthermore, the ultrasound dimension can give the visual representation of the intrauterine embryo (intrauterine) fetal biometric measurements in emergency cases, or determine the incidence of intrauterine embryo death or intrauterine fetal death, early diagnosis of which is excessively essential for the prevention of maternal morbidity and mortality.
First trimester Transvaginal Ultrasound scan is occasionally performed to confirm the pregnancy localization, the assessment of embryo viability and the embryo Gestational Age. The assessment of fetal biometry is usually based on the comparison of measured values with predicted values. Measurement of embryonic or fetal size using the greatest length of the embryo or fetal Crown–Rump Length (CRL) can be used to accurately determine the Gestational Age (GA) of a normal first trimester pregnancy to within three to five days. The correlation of four basic parameters, which are measured by the ultrasound scan, specifically: embryonic Crown–Rump Length (CRL), Heart Rate (HR), intrauterine Gestational Sac Diameter (GSD) and Yolk Sac Diameter (YSD) are closely associated with two controversial clinical scenarios: the initial scan can demonstrate alive embryo with cardiac pulsation, but subsequently intrauterine embryo death or intrauterine fetal death can be diagnosed, medically termed as ‘complete or incomplete miscarriage’. It is of vital importance for pregnancies at high risk of severe complications, such as early growth restriction, spontaneous embryo death, spontaneous embryo vanishing and recurrent late miscarriage.
Using the above–mentioned ultrasound measurements of an alive embryo/fetus, ultrasonographers can distinguish ongoing viable pregnancy or subsequent intrauterine fetal death with following miscarriage by determining the prognostic value of a yolk sac or fetal heart pulsation seen during an early Transvaginal Ultrasound.
Both gynecologists and ultrasonographers accept the ‘embryonic’ period by speaking about ‘fetal heart action’ and ‘fetal activity’ before the end of organogenesis (durability of embryonic period is the first 8 post–fertilization weeks, during which organogenesis takes place, thereafter, the fetal period is characterized primarily by growth). The term ‘fetus’ receives an ultrasound definition that includes fetal heart activity and/or a crown–rump length >10 mm [Farquharson et al., 2005]. The embryonic period (the first 10 weeks of pregnancy) is critical, since abnormal growth or abnormal development are likely to have a great impact on fetal growth in the second and third trimester of pregnancy and subsequent health of the neonate, that is why ultrasound monitoring of early pregnancy is the great diversity with many visualized criteria of viability, which are not absolute and should be systematically re–evaluated.
Recent advised conclusions recommend that a diagnosis of an empty sac (previously named ‘anembryonic pregnancy’, ‘early embryonic demise’ or ‘embryo loss’) should not be made if the visible crown–rump length is less than 6 mm, as only 65% of normal embryos will display cardiac activity. Repeat Transvaginal Ultrasound examination after at least a week, showing identical features and/or the presence of fetal bradycardia, is strongly suggestive of impending miscarriage [Farquharson et al., 2005].
In pregnancies at <7 weeks’ gestation the embryonic crown and rump cannot be visualized and therefore the embryonic crown–rump length is proposed to be measured as the greatest length of the embryo. From seven gestational weeks it is suggested to measure the embryonic crown–rump length in a sagittal section of the embryo with exclusion of the yolk sac. The heart rate can be calculated as beats per minute by the software of the ultrasound. The Gestational Sac diameter can be calculated as the average of three perpendicular diameters with the callipers placed at the inner edges of the trophoblast. The yolk sac diameter can be calculated as the average of three perpendicular diameters with the callipers placed at the centre of yolk sac wall [Papaioannou et al., 2011].
The configuration of embryonic crown–rump length, heart rate, intrauterine Gestational Sac diameter and yolk sac diameter reflects the most essential patterns for further embryo development. The inverse correlation between embryonic crown–rump length (if embryonic crown–rump length at the time of the early pregnancy scan is <12 mm it must be considered as a strong indicator of negative outcome) and miscarriages (most of all embryonic deaths, either resulting from lethal abnormalities (including the high occurrence of bradycardia as a leading or secondary factor) or placental failure, occur before the eighth week of pregnancy [Papaioannou et al., 2011].
Concluding the issue, concerning an early Transvaginal Ultrasound scan, it should be underlined that Transvaginal Ultrasound scan is an important modality in embryological research mainstream and in detection of embryonic developmental abnormalities in the early first–trimester pregnancy. The final diagnosis of a viable pregnancy can be made at the 11–14–week ultrasound scan. Miscarriage should be defined as the absence of a previously visible Gestational Sac, when the Gestational Sac remained without an embryo or embryonic cardiac activity ceased within the first trimester.
Conclusion
The implementation of high–resolution Transvaginal Ultrasound into clinical practice is of excessive importance for an accurate distinguishing of not only a viable embryo/fetus or non–viable embryo/fetus, but also many other adverse complications, which can lead to maternal and fetal mortality and morbidity.
The controversy could appear thereafter early intrauterine pregnancy was established as ideally, it is impossible to predict further embryo viability, its developmental normality or pregnancy failure, that is why intrauterine pregnancy of uncertain viability can be diagnosed.
Intrauterine Pregnancy of Uncertain Viability (PUV) is defined as the Transvaginal Sonographic (TVS) visualization of a small intrauterine Gestational Sac without demonstration of embryonic cardiac activity [RCOG, 2006]. The finding can indicate a normal early pregnancy of approximately 4–6 weeks’ Gestational Age [Goldstein et al., 1991] or a failed or failing pregnancy with arrested or reduced growth, which is destined to miscarry [Jurkovic et al., 1995]. Therefore, it is highly recommended to repeat periodically the ultrasound monitoring with inclusive interpretation and documentation in the pregnancies’ histories of the received results.
Complexities and dilemmas interconnected with early intrauterine pregnancy ultrasound guidance were inclusively discussed with the following conclusions made. Informative pathological markers as the vital indicators of the emergencies were represented. The recommendations concerning preventive measures were given.
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