The sixth batch of Mansoura Manchester programme

The sixth batch of Mansoura Manchester programme
Professor: Alaa Mosbah , Mansoura Manchester programme

Thursday, December 27, 2007

Guidelines For First Trimester Ultrasound Examination

1. INTRODUCTION Recent advances in ultrasonographic technology enable detailed studies and evaluation of the rapidly developing embryo in vivo. It is at present the most accurate and reliable method for the evaluation of first trimester pregnancies and their complications. However, the precise role of ultrasound in the first trimester is still in evolution, mainly because of rapid development and availability of newer generations of ultrasonographic equipment, which enables better and earlier visualization of embryonic structures. The correct use and interpretation of first trimester ultrasound examination requires a good understanding of normal early embryonic developmental milestones and ultrasonographic landmarks. 2. AIMS Part I of this guideline examines the use of ultrasound examination in the management of women with pregnancy complications in the first trimester, and the basic requirements of such an examination. The role of routine first trimester ultrasound examination and the safety of such examination will be examined in Part II of this guideline. 3. INDICATIONS An ultrasound examination may provide valuable information to assist patient management in, but not limited to, the following clinical conditions in the first trimester of pregnancy: 3.1 Confirmation of the presence of normal intrauterine pregnancy3.2 Estimation of gestational age3.3 Confirmation of embryonic life or early pregnancy failure3.4 Evaluation of the cause of vaginal bleeding3.5 Evaluation of suspected ectopic pregnancy3.6 Confirmation of multiple pregnancy3.7 Evaluation of suspected pelvic, ovarian or uterine pathology. 4. NORMAL ULTRASONOGRAPHIC EMBRYONIC DEVELOPMENTAL MILESTONESTable 1 shows some important ultrasonographic milestones during early pregnancy. The earliest detectable ultrasonogrraphic evidence of pregnancy is thickening of the decidua at approximately 3 to 4 weeks of menstrual age. This sign, however, is non-specific and therefore carries no significant value for clinical management of early pregnancy complications. Table 1. Important transvaginal ultrasonographic milestones Gestational age (Menstrual day) CRL (mm) Signs3 to 4 week - Thickening of endometrium and decidua4 to 5 week - First appearance of gestational sac5 week 1-2 First appearance of yolk sac and embryonic pole5 to 6 week 5 Embryonic cardiac activity By about 4.5 week, a small 2-3 mm gestational sac, which represents the chorionic cavity, can be visualized by transvaginal sonography (TVS). This is the first reliable sonographic evidence of pregnancy. The gestational sac does not lie within the endometrial space but is intradecidual, and is sonographically surrounded by an echogenic ring of trophoblastic and decidual reaction. These features assist the differentiation between a small true gestation sac from collection of blood or fluid within the uterine cavity, although such distinction could sometimes be difficult. Visualization of the yolk sac/embryo complex is diagnostic of an intrauterine pregnancy and excludes blighted ovum. The yolk sac should always be seen with TVS when the gestational sac reaches a mean diameter of 8 mm at 5 to 6 week. With TVS, embryos as small as 1 to 2 mm may be identified at similar stage of pregnancy. Although embryonic cardiac activity may be demonstrable in some pregnancies as early as 35 days after onset of last menstrual period, or in embryos as small as 1 mm, the absence of cardiac activity at such early stage could be normal. Embryonic activity, however, should always be observed by TVS when the crown-rump length (CRL) is 5 mm or more1. It is important to realize that these milestones represent the average development of a normal pregnancy. The ability to demonstrate these sonographic milestones is not only affected by biological variations between individuals but also the quality of the ultrasound scanner, the frequency of the transducer, and the experience of the operator. In general, the same milestone is expected to be visualized 1 week later if transabodminal ultrasonography (TAS) is used (Table 2). In case of uncertainty, one should always act on the safe side and request a repeat examination later. Table 2. Average time of detection of Various Parameters in Early Pregnancy by Ultrasonography (Menstrual day) Transabdominal Transvaginal Gestational sac Day 35-37 (5 mm f) Day 29-31 (2 mm f)Yolk sac Day 42-45 Day 35-37Embryo Day 45 - 46 (~ 5 mm) Day 35-40 (~ 2 mm)Heart motion Day 42 - 45 Day 35 - 37 5. EARLY INTRA-UTERINE DEMISEFor diagnostic purpose, the most important question is beyond what point, i.e. the discriminatory level, the absence of yolk sac or fetal cardiac activity can be considered definite signs of early pregnancy failure. Using TVS, visualization of a discrete embryo >5 mm without fetal cardiac activity can be considered diagnostic of embryonic demise2,3. If the embryo is less than 5mm, the absence of cardiac activity could be normal and a repeat sonogram should be performed at least 1 week apart. If only TAS is performed, the discriminatory level should be at least 9 mm3. In the absence of an embryonic pole, the major sonographic diagnostic criterion of early pregnancy failure is a large gestational sac without a yolk sac (i.e. a condition also called blighted ovum or anembryonic pregnancy). Using TAS, an mean sac diameter (MSD) <>