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Ultrasound in obstetrics

ultrasound in obstetrics

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Ultrasound in obstetrics

  1. 1. •developed by professor Langevin for the French and British admiralties during the first world war to combat the growing menace of submarines. •It was formerly referred to as SONAR which stands for “sound, navigation and ranging”
  2. 2. •Sir Ian Donald was the first to demonstrate and document the application of this technology to medical diagnosis. •His pioneering efforts were published in The Lancet of 7 June 1958 which described his experience with ultrasound for the diagnosis of a large ovarian cyst
  3. 3. •An ultrasound scanner consists of transducers (probes) that transmit and receive ultrasound waves, a screen to view the image and its technical data, and a variably sophisticated control panel.
  4. 4. • Ultrasound waves result from an inverse piezo-electric effect. • The piezo-electric effect refers to the phenomenon that takes place when pressure is applied to the surface of certain crystals referred to as piezo-electric materials : the mechanical pressure produces an electric current.
  5. 5. •Inversely, when an electrical pulse is applied to piezo- electric material, a mechanical wave results and this mechanical wave is the ultrasound beam. •When these wave meet the tissue interface, they are reflected back to the transducer and converted to an electric signal, which is processed and displayed as the ultrasound image on the monitor. •The amount of beam reflected back is proportionate to the difference in the acoustic densities of the tissues meeting at the interface
  6. 6. • When the acoustic densities are markedly different such as when striking calcification, bone, stones and air, nearly the whole beam is reflected back and the image is echo-rich.
  7. 7. •If the acoustic density differences are small, low level echoes result and if the acoustic densities are identical as in homogeneous fluids like blood, amniotic fluid and urine, the entire wave is transmitted and none is reflected resulting in an echo-free image. •Because air is a poor transmitter of high-frequency sound waves, soluble gel is applied to the skin to act as coupling agent. •The processor computes the location (depth) of the signal based on time differences between transmitting and receiving.
  8. 8. • Obstetric ultrasound employs frequencies of 2 to 15 Mhz. • Higher frequency transducers have higher spatial resolution. This means they can better differentiate two closely located side-by-side spots in the region of interest. • The penetration of high frequency wave is however limited. Therefore, high frequency probes are used to look at near structures and lower frequency probes are used to study tissues at depth.
  9. 9. •Abdominal transducers use a frequency of 2 to 6.5 MHz and transvaginal transducers use frequencies of 5 to 15 MHz. •Obstetric ultrasound uses a largely abdominal approach. •Transvaginal scanning is used in the first trimester for more accurate information on early pregnancy complications and delineation of fetal morphology, assessing the cervical length and other features of incompetence, delineation of cranial anatomy in the deeply engaged head and in some situations of suspected placenta previa and vasa previa.
  10. 10. •Conventionally, the left of the screen indicates the head- end of the patient in a longitudinal section or the right side of the patient in a transverse section. The top of the screen is anterior and the bottom posterior. •When imaging the fetus in the second and third trimesters, these orientations are no longer relevant.
  11. 11. •Echo-free structures and lesions are also referred to as anechoic, sonolucent, fluid or echolucent. •Echo-rich structures are also called heperechoic, echogenic, echo-bright or solid. •Structures with few echoes are referred to as echo-poor, echopenic or hypoechoic.
  12. 12. •A-mode studies were the most primitive forms of ultrasound imaging and consisted of a graph indicating reflectors at the level of their depth. •These are no longer used in obstetrics.
  13. 13. •B-mode studies are currently in use and are what we mean by conventional ultrasound now. • These indicate reflections arranged along two axes in the region of interest. •B-mode studies currently use a grey scale which reflects the intensity of the signal and imparts texture to the image. The other attribute of B-mode studies is real-time.
  14. 14. •In the real-time mode, the image moves in the same manner as the region of interest moves in real life. •The conventional ultrasound scan today is, therefore, a real-time grey-scale B-mode study. This is also known as 2D study.
  15. 15. •It is now possible to add a third dimension to the image which is made possible by a special transducer and computer software arrangement, and is referred to as 3D ultrasound. •Real-time 3D ultrasound is known as 4D ultrasound.
  16. 16. •The tern M-mode refers to a motion mode in B- mode studies. •This is currently employed in obstetrics to evaluate fetal cardiac motion to assess heart rate and rhythm as well as for studying the excursions of the cardiac valves and the myocardium.
  17. 17. • Confirm an intrauterine pregnancy • Evaluate a suspected ectopic pregnancy • Define the cause of vaginal bleeding • Estimate gestational age • Diagnose or evaluate multifetal gestations • Confirm cardiac activity • Assist chorionic villus sampling, embryo transfer, and localization and removal of an intrauterine device
  18. 18. •Assess for certain fetal anomalies, such as anencephaly, in high-risk patients •Evaluate maternal pelvic masses and/or uterine abnormalities •Measure nuchal translucency when part of a screening program for fetal aneuploidy •Evaluate suspected gestational trophoblastic disease
  19. 19. EMBRYONIC EVENTS •day 14: ovulation •day 15: fertilization •day 18: morula stage •day 20: blastocyst stage- beginning of implantation •Day 23: implantation complete •Days 27-28: formation of secondary yolk sac •Days 21-28: proliferation of syncytiotrophoblast
  20. 20. ULTRASOUND FINDINGS •Implantation- conceptus measures 0.1mm & cannot be detected by the available ultrasound equipment •trophoblastic flow with transvaginal color flow doppler – increased blood flow velocity in the endometrium is due to invasion of decidua by chorionic villi.
  21. 21. •EMBRYONIC EVENTS •day 29-30: gastrulation; formation of 3 primary germ layers •days 31-42: neurolation; formation of neural plate & neural tube •Day 35: primitive cardiovascular system consisting of heart & a vascular network in the embryo, yolk sac, connecting stalk & chorion
  22. 22. ULTRASOUND FINDINGS Gestational sac: Frequency at least 5 MHZ with TVS Size-2-3mm MSD Wks-4wks3d to 4wks 5d yolk sac: 5.5 wks GA - MSD 8mm (TVS) can be earliest seen with MSD 5mm & should always be evident by MSD 8mm 6 to 7 wks GA- MSD 15 to 20 mm (TAS)
  23. 23. Methods Serum B hcg level in IU/ml TVS--------- ------1000 TO 2000 TA-------------------6000 Yolk sac------------7000 Embryo---------------11,000
  24. 24. Small fluid collection surrounded completely by an echogenic rim Echogenecity of rim should exceed the level of myometrial echoes Position- fundus or in mid to upper uterus & is always abutting the endometrial canal GA in days=Gestational sac (MSD) size in mm +30
  25. 25. THRESHOLD LEVEL: • lowest B-HCG level by which a normal intrauterine gestational sac is possible to be identified DISCRIMINATORY LEVEL: • level above which gestational sac must be visualized • 1000 MIU/ml for TVS
  26. 26. •Confirms- early intrauterine pregnancy •1st recognizable structure inside the gestational sac & should be seen when MSD is 8-10mm. •Normal yolk sac diameter in 1st trimester 3-6mm •Increases steadily by 0.1mm per day until 10 wks GA to a maximum of 5 to 6mm •Abnormal yolk sac size & morphology cannot be used as absolute predictors of pregnancy outcome & need serial evaluation to confirm or exclude an abnormal outcome
  27. 27. • following changes assessed by 2D US are related to spontaneous abortion procedure  absence of yolk sac Too large - >6mm Too small - <3mm Irregular shape- mainly wrinkled with indented walls Degenerative changes- abundant calcifications with decreased translucency of yolk sac Number of yolk sacs- has to be equal to the number of the embryos
  28. 28. •MSD=10mm •Consists of decidua parietalis( lining the uterine cavity) & decidua capsularis (lining the gestational sac) seen as 2 concentric rings surrounding an anechoic gestational sac •TAS-5 to 6 wks GA •Confirms intrauterine pregnancy
  29. 29. •Gestational sac in which embryo failed to develop or died at a stage too early to visualize •Diagnosis- absence of embryonic echoes within the gestationl sac, large enough for such structures to be visualized, independent of the clinical data or menstrual cycle. •If the volume of the sac is 2.5ml & is not increasing in size by at least 75% over a period of 1 week, the definition of this pathological condition in early pregnancy is a blighted ovum. •A large empty sac usually measures 12-18mm in diameter
  30. 30. By Transabdominal approach By TVS MSD development 10 mm No double decidual sign 20 mm No yolk sac 25 mm No embryo with cardiac activity MSD development 8 mm no Yolk sac 16 mm No cardiac activity
  31. 31. METHODS GA in wks MSD in mm CRL TVS 6 TO 6.5 13 TO 18 4mm TAS 8 25 9mm
  32. 32. •If CRL is less + no cardiac activity -Expectant management with follow up usg -Use B hcg for follow up •If CRL is more + no cardiac activity -Non viable gestation is likely
  33. 33. GA in wks HEART RATE 6 110 TO 115 8 140 TO 170 9 137 TO 144
  34. 34. structure Gestational age spine 7-8wks Upper limbs 7 wks Lower limbs 8 wks Feet & hands End of 10th wk Fingers & toes 11 wks Maxilla & mandible 9th wk
  35. 35. •The distance from the top of the head( crown) to the bottom of the buttocks (rump) •Measured with embryo in neutral position with no flexion or extension •Mean of 3 readings • to assess gestational age from 5 wks 3 days to 13 wks 6days
  36. 36. GESTATIONAL AGE IN WEEKS CRL in cm 6.1 0.4 7.2 1.0 8.0 1.9 9.2 2.5 9.6 2.9 10.5 4.0 12.2 5.5 13.2 6.9 14.0 8.0 Gestational age( in weeks) = CRL (cm) + 6.5
  37. 37. 1st trimester ultrasound <= 5days discrepancy between LMP & US estimate of GA >5 days discrepancy between LMP & US estimate of GA Choose LMP derived GA prediction Choose US derived GA prediction
  38. 38. •sonographic appearance of the subcutaneous accumulation of fluid in in the region of fetal neck. •Anechoic stripe •seen in all fetuses in early pregnancy.
  39. 39. •Chromosomal abnormality • cardiovascular (cardial septal defect, cardiac failure) •Pulmonary (diaphragmatic hernia), Increased in intra thoracic pressure, mediastinal compression causing venous congestion •Renal & abdominal wall defects, skeletal dysplasia ,infections, metabolic & hematologic disorders •Connective tissue abnormalities, alteration of extracellular matrix of skin (trisomy 21) •Delay in development of Lymphatic system(turners syndrome), •Fetal hypo proteinemia
  40. 40. • midline sagittal section • If facing towards the transducer- the fetal nasal bridge and the nasal tip should be visible in same view • If facing away from the transducer- the medulla ,pons and the thalamus should be visible in the same view. •11wks to 13wks 6days •CRL 45-84mm •Magnification of 75% such that only head & thorax occupy the whole screen
  41. 41. •At the widest space of the NT •Calipers placed “on to on” in transonic space perpendicular to long axis of fetus •Biggest of 3 measurements •TAS preferable, but depending on fetal position TVS can be done •Exclude the presence of umbilical cord near neck •Fetal neck in neutral position
  42. 42. NORMAL VALUES Cut off at 3.5mm across 11-13 wks CRL NT 45mm 1.2 -2.1mm 84mm 1.9-2.7mm
  43. 43. •ACOG recommends that patients who have fetal NT >=3.5mm in 1st trimester despite a negative aneuploidy screen or normal fetal chromosomes should be offerd a targeted ultrasound examination,fetal echocardiogram or both. •A pregnancy should never be terminated on the basis of this finding alone.
  44. 44. •downs syndrome •turner’s syndrome •trisomy 18 •trisomy 13 •triploidy various other fetal defects and genetic syndromes with normal no. of chromosomes.
  45. 45. Absent or hypoplastic in: o69% fetuses with trisomy 21 o50% of trisomy 18 o40% trisomy 13 o1.4% of chromosomally normal fetuses
  46. 46. •Transducer should be parallel to the direction of nose •3 lines will be visible  skin- top line Echogenic nasal bone just below this which is thicker than the overlying skin 3rd line in front of nose – tip of nose
  47. 47. NASAL BONE PRESENT: if more echogenic than overlying skin ABSENT: Not seen or echogenicity <= skin
  48. 48. •Assessment of nasal bone is not yet recommended in routine clinical practice •studies show that Nasal bone not incorporated in 1st trimester screening Nasal bone incorporated DETECTION RATE FOR DOWNS SYNDROME 81.8% FALSE POSITIVE 5.4% 90.9% FALSE POSITIVE 3.7%
  49. 49. •It is the quantification of the flat facial profile seen in fetuses with trisomy 21 •As maxilla is small & set back in these fetuses, the angle becomes wider •INCREASED IN: 5% euploid fetuses 45% trisomy 21 55% trisomy 18 45% trisomy 13
  50. 50. •Angle between line drawn along superior surface of the palate & a line drawn from anterosuperior corner of the maxilla to the anterior surface of frontal bone
  51. 51. •It is the quantification of the flat facial profile seen in fetuses with trisomy 21 •As maxilla is small & set back in these fetuses, the angle becomes wider •INCREASED IN: 5% euploid fetuses 45% trisomy 21 55% trisomy 18 45% trisomy 13
  52. 52. •Angle decreases with increase in CRL •Assessment of facial angle in addition to NT inreases detection rate of trisomy 21 from 90 to 94% GA CRL FMF ANGLE 11weeks 45mm 83 13weeks 6 days 84mm 75
  53. 53. •Abnorml ductus venosis flow in the 11-13wks 6days scan is associated with chromosomal anomalies, cardiac abnormalities, & adverse fetal outcomes •Reversed flow in a wave is observed in: • 3.7% euploid fetuses • 70% fetuses with trisomy 21, 18 & 13. •However in 80% fetuses with reversed a waves pregnancy has a normal outcome •When combined with NT- detection rate of trisomy 21 increases from 94 to 97%
  54. 54. •Increases risk of trisomy 21 & cardiac defects •The incidence is correlated with nuchal thickening & decreases with increasing CRL. •Fetus should not be moving •Apical 4 chamber view is obtained & magnified so that entire screen is occupied by thorax •Fetuses with TR with normal karyotype should be followed carefully to assess for cardiac anomalies.
  55. 55. COMPLETE MOLE •Enlarged uterus •Classic sonographic apperarence- solid collection of echoes with numerous small (3-10mm) anechoic spaces (snowstorm or granular apperance) •Molar tissue- bunch of grapes sign which represents hydropic swelling of trophoblastic villi •Variable apperance •No identifiable fetal tissue
  56. 56. COMPLETE MOLE
  57. 57. PARTIAL MOLE •placenta enlarged & contains areas of multiple diffuse anechoic lesions •Fetus with severe structural abnormalities or IUGR, oligohydramnios, or deformed gestational sac may be noted
  58. 58. PARTIAL MOLE
  59. 59. TUBAL/ ADNEXIAL RING SIGN OR BAGEL/ DONUT SIGN • extrauterine gestational sac (fluid filled) with echogenic ring which surrounds an unruptured ectopic pregnancy. • has a 95% positive predictive value for ectopic pregnancy
  60. 60. TWIN PEAK SIGN/ LAMBDA SIGN •triangular projection of trophoblastic tissue isoechoic with placenta insinuating between the layers of inter twin membrane from the placental surface •100% predictive of dichorionic pregnancy •In 2nd trimester regression of chorionic frondosum leads to the gradual loss of lambda sign T SIGN •Refers to lack of chorion extending between the layers of inter twin membrane denoting a monochorionic pregnancy •The intertwin membrane comes to an abrupt halt at the edge in a T configuration
  61. 61. •Ian Donald’s practical obstetric problems, 7th edition •William’s obstetrics, 24th edition •Peter W. Callen ultrasonography in obstetrics and gynaecology •Donald School textbook of of ultrasound in Obstetrics and Gynaecology 2nd edition
  62. 62. THANK YOU

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