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Basic Obstetric Ultrasound

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Basics of Ultrasound for Graduates By :
Dr.Ahmed Samy
lecturer of Obstetric & Gynecology
Cairo University

Published in: Health & Medicine
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Basic Obstetric Ultrasound

  1. 1. By Dr.Ahmed Samy lecturer of obstetric& gynecology Cairo university
  2. 2.  Definition of Ultrasound Ultrasound means sound waves of frequency higher than those heard by the human ear. SAFETY no definite complications for diagnostic ultrasound when the frequency used is less than 10 MHz Ultrasound in diagnostic obstetrics and gynecology is used in the range between 3-8 MHz
  3. 3.  Ultrasonic Fetal Heart Detectors (Doppler Apparatus).  Real-time Ultrasound Imaging Systems. two-dimensional ultrasound (2D) three and four-dimensional ultrasound (3D/4D) color Doppler ultrasound.
  4. 4.  A- In normal pregnancy The early pregnancy scan Mid-pregnancy Scan (Anomaly Scan) Late Pregnancy Scan.  B- In abnormal pregnancy
  5. 5. Timing  From 10-13 weeks is best for early detection of trisomy.  From 5-8 weeks is best for early detection of ectopic pregnancy.
  6. 6.  Trans-vaginal if 5-8 weeks.  Trans-abdominal if 10-13 weeks.
  7. 7.  Accurate Evaluation of gestational age Using crown-rump length (CRL)  accuracy close to +/- 4 days.  Early Detection of Ectopic Pregnancy  Early Exclusion of trisomy 21(congenital abnormalities)  establish the presence of a living embryo/fetus
  8. 8. Obstetrical ultrasound is a useful clinical test to:  establish the presence of a living embryo/fetus.  estimate the age of the pregnancy.  diagnose congenital abnormalities of the fetus.  evaluate the position of the fetus.  evaluate the position of the placenta.  determine if there are multiple pregnancies.  determine the amount of amniotic fluid around the baby.  check for opening or shortening of the cervix.  assess fetal growth.  assess fetal well-being.
  9. 9.  You should wear a loose-fitting, two- piece outfit for the examination  Only the lower abdominal area needs to be exposed during this procedure.  In early pregnancy US, full bladder is necessary.  In transvaginal US, empty bladder is necessary.
  10. 10. Console The transducer Abdominal probes. Endocavitary probes: Trans-vaginal & Trans-rectal. a video display screen
  11. 11.  the patient is positioned lying face-up on an examination table that can be tilted or moved.  A clear water-based gel  help the transducer make secure contact with the body  eliminate air pockets between the transducer and the skin  The sonographer  presses the transducer firmly against the skin in various locations  sweeps over the area of interest.  angling the sound beam from a farther location to better see an area of concern.
  12. 12.  Transvaginal ultrasound is performed very much like a gynecologic exam and involves the insertion of the transducer into the vagina after the patient empties her bladder, lying on her back, possibly with her feet in stirrups.  A protective cover is placed over the transducer, lubricated with a small amount of gel, and then inserted into the vagina.  Only two to three inches of the transducer end are inserted into the vagina  The images are obtained from different orientations to get the best views of the uterus and ovaries.
  13. 13.  Most ultrasound examinations are painless, fast and easy, usually no discomfort from pressure.  If scanning is performed over an area of tenderness, you may feel pressure or minor pain from the transducer.  With transvaginal scanning, there may be minimal discomfort as the transducer is moved in the vagina.  Once the imaging is complete, the gel will be wiped off your skin.
  14. 14.  Earliest sign of pregnancy  seen at 4-4.5 weeks  It is intradecidual  Surrounded by decidual reaction  Can be used for dating.  A normal gestational sac grows by 1 mm per day.
  15. 15.  its normal eccentric location: it is embedded in endometrium, rather than centrally within the uterine cavity  presence of a yolk sac : seen at approximately 5.5 weeks or with a beta- HCG of ~7000m IU/ml  presence of the double decidual sign
  16. 16.  Seen at 5 weeks gestation  Differentiates true from pseudo gestational sac  Seen at 20 mm sac diameter abdominally and 8 mm sac diameter vaginally
  17. 17.  Seen at 6 weeks vaginally  Should be seen at sac diameter of 18mm vaginally and 25mm abdominally  Heart beat is seen at CRL of 5mm vaginally
  18. 18.  Gestational sac – 4 to 5 weeks  Yolk sac – 5 to 6 weeks  Fetal pole - 6 to 7 weeks  Cardiac Activity - 6 to 7 weeks.
  19. 19.  Failed early pregnancy refers to the death of the embryo and therefore, miscarriage.  The most common cause of embryonic death is a chromosomal abnormality.
  20. 20. A pregnancy is considered non-viable on transvaginal ultrasound if:  no fetal heart beat where: › CRL ≥ 7 mm  no fetal pole where: › MSD > 25 mm with no embryo  Both fetus and gestational sac are expected to grow 1mm/day. Hence, absence or inadequate growth on serial scans at least 7-10 days apart is suggestive of non-viability.
  21. 21.  no yolk sac, where: › MSD > 8 mm › embryo seen  irregular gestational sac  low position of the gestational sac
  22. 22.  Normally BHCG doubles every 48hours  Discrimination zone: relies on BHCG increasing by >66% in 48 hours, if not and no considerable bleeding think of ectopic pregnancy if uterus is empty on scan  However 5% of normal pregnancies don’t behave like that
  23. 23.  Direct visualization of ectopic pregnancy  Only seen in 10-20% of ectopic pregnancies  Empty uterus
  24. 24.  Empty Uterus  Pseudo gestational sac
  25. 25.  Sac is intra-decidual  No yolk sac or fetal pole at sac diameter of 25 mm or more transvaginally  Sac can be irregular  Low uterine position  Weak decidual reaction  If unsure repeat in 1 week
  26. 26.  Clinical presentation  Snow storm appearance  Very High BHCG  Theca lutein cysts in both ovaries  Always check pathology
  27. 27.  The ovaries are commonly the site for theca lutein cysts secondary to the BHCG.
  28. 28.  Gestational sac seen at 4.5 weeks  Yolk sac seen at 5 weeks  CRL seen at 6 weeks with sac diameter of 20mm  Heat beat seen at CRL of 5mm  If too early or unsure repeat in 1 week
  29. 29.  It is essential to accurately date the pregnancy for adequate timing of delivery, management of post-maturity and small for gestational age.  Use LMP if regular periods and certain dates, then first trimester ultrasound to confirm dates
  30. 30.  Visible form 4.5 weeks by T.V scan  Implanted on one side of the uterine cavity  As the sac is not usually round, an average of the length, width and depth is made.  The accuracy of dating using GS size is low and can be off by a whole week  This is therefore not recommended
  31. 31.  Before placental circulation is established, the yolk sac is the primary source of exchange between the embryo and the mother.  In a normal early pregnancy, the diameter of the yolk sac should usually be < 6 mm while its shape should be near spherical.  Natural course As the pregnancy advances, the yolk sac disappears and is often sonographically not detectable after 14 weeks
  32. 32.  Absence of the YS in the presence of an embryo is always abnormal and is associated with fetal demise.  A larger than normal YS is also associated with adverse outcome in the fetus  Visualization of multiple yolk sacs is the earliest sign of a polyamniotic pregnancy, e.g. twins.
  33. 33.  Measure from top of head to rump  Always measure in neutral position  made between 7 to 13 weeks  Very accurate(Dating with the CRL can be within 3-4 days of LMP)  it should not be changed by a subsequent scan.
  34. 34. • Standard – Anatomic Survey • Limited – Targeted to answer a question • Specialized – Targeted anatomic
  35. 35. • Fetal biometry • Fetal Cardiac Activity • Fetal Lie • Fetal Number • Placental Location • AFI • BPP/Modified BPP
  36. 36.  Bi-parietal diameter  Occipto-frontal diameter  Head circumference  Abdominal circumference  Femur length  All can be + or – 2 weeks
  37. 37. Landmarks :  Midline Falx cerebri  Cavum septum pellucidum  Thalami symmetrically positioned on either side of the falx  Lateral ventricle
  38. 38.  The diameter between the 2 sides of the head  This is measured after 13 weeks.  Dating using the BPD should be done as early as is feasible.  Different babies of the same weight can have different head size, therefore dating in the later part of pregnancy is generally considered unreliable  The BPD remains the standard against which other parameters of gestational age assessment are compared  A wrong measurement plane can produce errors up to 20mm !
  39. 39.  The measurement is taken from the outer edge of the near cranium to the inner edge of the far cranium.  a middle-to-middle measurement is also acceptable.  The BPD can be smaller (and sometimes much smaller than is expected) in fetuses with flatter heads(check the head circumference)
  40. 40. Landmarks:  Same as BPD  On the outer margin of the bony skull  Independent of skull shape  More indicative of gestational age
  41. 41.  serves as a monitor for growth of the long bones.  The femoral shaft is seen as a slightly curved, echogenic structure that produces an acoustic shadow
  42. 42.  The longest dimension of the femoral shaft is measured for the FL  The transducer should be aligned along the long axis of the bone should include measurement of the entire diaphysis.  The femoral epiphysis, seen as a spike on one end of the femoral shaft, is not included in the measurement.  The measurement is most accurate when the femur is perpendicular to the US beam
  43. 43.  Measures the longest bone in the body and reflects the longitudinal growth of the fetus  The use of FL in dating is similar to the BPD, and is not superior unless a good plane for the BPD cannot be obtained or that the head has an abnormal shape.  Similar to the BPD, dating using the FL should be done as early as is feasible.  The FL is a mandatory measurement  the FL has a very important function of excluding dwarfism in the fetus.
  44. 44.  The extension to the greater trochanter and the head of femur should not be included  The measurement is also consider inaccurate when the femur image is at an angle of over 30 degrees to the horizontal.  measurement of the FL is considered accurate only when the image shows two blunted ends.
  45. 45.  Do not take an average of the BPD and FL for dating, because you can always have a fetus with an average size head and a longer or shorter than average lower limb  The measurements should be reported as they are. Do not take an average.
  46. 46.  Appropriate plane › U/S beam should be perpendicular to the bone › Measurement is made along the femur diaphysis › Exclude the distal femoral diaphysis
  47. 47. Landmarks: o Spine + rib o Stomach o Part of portal vein o Picture should be as round as possible
  48. 48.  The single most important measurement to make in late pregnancy  It reflects more of fetal size and weight rather than age.  Serial measurements are useful in monitoring growth of the fetus.  AC measurements should not be used for dating a fetus.  It is also a mandatory measurement.
  49. 49. Plane  The best plane is the one in which the portal vein is visualized in a tangential section.  The plane in which the stomach is visualized is also acceptable.  The outer edge of the circumference is measured  On screen computer-generated elliptical measurements probably yield the best results
  50. 50. • Fetal Cardiac Activity. • Fetal Lie • Fetal Number • Placental Location • AFI • BPP/Modified BPP
  51. 51. Positive cardiac activity Fetal death › Absence of cardiac activity for at least 2-3 minutes › Ideally confirmed by two or more examiners
  52. 52.  Lie - relationship of long axis of fetus to the long axis of the mother › Longitudinal › Transverse › Oblique  Presentation – part of the fetus closest to maternal pelvic inlet or cervix › Cephalic (vertex, sinciput, brow, face) › Breech › Shoulder › Compound
  53. 53. When  The earliest time is 12 weeks if in right position  Best done between 17-20 weeks gestation  What you will see????  Male: penis or scrotum  Female: The 3-lines sign which denotes the labia
  54. 54.  The absence of the penis must not be taken as sufficient evidence of the fetus being a girl AGAIN MALE:dome shaped genital swelling with a cephalic-directed phallus FEMALE:three or four parallel lines representing the labia
  55. 55.  Anterior/Posterior/Lateral/Fundal  Placenta Previa › Marginal › Partial › Complete  Low-Lying
  56. 56.  Inner border of placenta against the uterine wall has the combined hypoechoic myometrium and interposed basilar layer = hypoechoic band called the decidua basalis (contains maternal blood vessels)  Outer surface abutting the amniotic fluid = chorionic plate (chorioamniotic membrane) = bright specular reflector  Placental thickness judged subjectively But if measure at mid position or cord insertion 2-4 cm = normal
  57. 57. Placental calcification. Scan of posterior placenta at 39 wks shows calcification along the basal plate (arrows), chorionic plate (open arrows), and septa (arrowheads
  58. 58. Midline sagittal scan at 28 weeks shows the posterior placenta (P) completely covering the cervix (C). B, maternal bladder
  59. 59. the placenta had invaded through the myometrium to the bladder wall
  60. 60.  Combination of NST with 4 real-time ultrasound observations  2 points given to each observation that is normal or present  Maximum 30 minute time frame.  Each of the 5 components of the biophysical profile score do not have equal significance. Fetal breathing movements, amniotic fluid volume, and the non-stress test are the most powerful variables.
  61. 61. Components of the 30 minute Biophysical Profile Score Component Definition Fetal movements > 3 body or limb movements Fetal tone One episode of active extension and flexion of the limbs; opening and closing of hand Fetal breathing movements >1 episode of >30 seconds in 30 minutes - Hiccups are considered breathing activity. Amniotic fluid volume A single 2 cm x 2 cm pocket is considered adequate. Non-stress test 2 accelerations > 15 beats per minute of at least 15 seconds duration.
  62. 62. Modified BPP Combines › NST (short-term indicator of acid/base status) › AFI  Considered normal if NST is reactive and AFI is >5 cm
  63. 63.  Positive end diastolic  flow Absent / Reverse EDF in Umbilical Artery of Donor
  64. 64.  Low resistance can be a sign of redistribution of blood in the foetus in cases of IUGR
  65. 65.  This is the last vessel to be affected in IUGR and is used to decide timing of delivery.
  66. 66.  Measure the dimensions of the largest vertical pocket of amniotic fluid.  Pocket of fluid <1cm = oligohydramnios 1-2cm = decreased fluid 2-8cm = normal >8cm = polyhydramnios  Controversies in cut-off criteria for oligohydramnios: › < 0.5 mm › < 1 cm › < 2 cm › < 3 cm
  67. 67.  Most reproducible/accurate  Technique(4 quadrant technique) Divide the uterus into four quadrants using the linea nigra as the vertical axis and the umbilicus as the horizontal axis.  Linear transducer head placed along mother’s longitudinal axis and held perpendicular to the floor in the sagittal plane. The pocket with the largest vertical dimension is measured in each quadrant. Sum of all four measurements = AFI
  68. 68.  Cord or extremities may traverse the pocket, but may not be measured as part of the vertical depth  Values <5cm = very low (oligohydramnios) 5-8cm = low 8-25cm = normal term AFI >25cm = polyhydramnios
  69. 69. • Excessive transducer pressure • Cord-filled pockets should not be used • Obese patients may introduce scatter that creates artifact echoes – May overcome with lower frequency transducer • Not measuring low in the uterine cavity
  70. 70.  https://www.facebook.com/doctorsask Or http://www.doctorsask.com
  71. 71. Dr Wafaa Hamed Dr Heba Ghanem
  72. 72. Thank you

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