Ultrasound is useful in the first trimester for evaluating bleeding, pain, gestational sac location and development. A gestational sac is normally visible by 4 weeks ultrasound. The yolk sac appears by 5 weeks and the embryo with cardiac activity by 6 weeks. Abnormal findings include lack of growth, irregular sac shape, large yolk sac size. Doppler can assess blood flow. Ectopic pregnancies can be detected by visualizing an embryo outside the uterus combined with serum hCG levels. Multiple pregnancies are determined by membrane thickness and number of yolk sacs.

1. FIRST TRIMESTER
ULTRASOUND
Dr Roshan Valentine
PG Resident
Dept od RadioDiagnosis
St Johns Medical College, bangalore

2. INTRODUCTION
 FIRST TRIMESTER
 Most critical and tenuous period of human dvpt
 Single cell into recognizable human being
 Till 12 weeks

3. INTRODUCTION
WHY
 Location and number of gsac
 GA
 Early pregnancy for normal appearance/impending failure
 Evaluate pain/bleeding in maternity
 Evaluate uterine contents before pregnancy termination
 Screening for fetal anomalies

4. NORMAL SONOGRAPHIC ANATOMY
IDENTIFYING THE GESTATIONAL SAC
 First definitive sonographic sign
 Earliest appearance :small round fluid collection(chorionic cavity)
surrounded completely by a hyperechogenic rim of tissue(chorionic villi
+ decidual tissue).
 Threshold(TVS) : 2-3mm size ; 4+1 weeks – 4+3 weeks
 Hyperechoic rim : 2mm thick , hyperechoic than myometrium
 GS measured as Mean Sac Diameter(MSD)

6. IDENTIFYING THE GSAC
 Normal position : mid – upper uterus
 Double decidual sac sign : growing sac deforms the central cavity giving
a double bubble appearance
 MSD : ≥ 10mm, 5-6 weeks (TAS)

7. IDENTIFYING THE GSAC

8. BLOOD FLOW IN EARLY PREGNANCY
 UTERINE ARTERY:
 At uterocervical junction
 High resistance flow with prominent diastolic notch(absent in some)
• diastolic notch – disappears by 2nd trimester
• Presence in 3rd trimester : umbilical cord and placental abnormalities
 SPIRAL ARTERY
 B/W myometrium and choriodecidual tissue
 Low resistance flows
 Changes to high velocity low resistance flow as pregnancy progress

10. IDENTIFYING THE YOLK SAC
 First anatomic structure within GS
 TVS : 5th week ; 5mm MSD
 Almost always : 5+5 weeks ; MSD 8mm
 TAS : by 7 weeks ; MSD 20mm
 Confirms IUP
 Highest possible transducer frequency
 Spherical in shape with sonolucent center and echogenic periphery
 Max diameter : 5-6mm ;CRL 30-45mm
 End of first trimester : no longer detected

12. INDENTIFYING EMBRYO AND CARDIAC ACTIVITY
EMBRYONIC DISK :
 Subtle focal thickening along the
periphery of yolk sac.
 THRESHOLD : 5-6 wks; MSD 5-12mm
CARDIAC ACTIVITY
 TVS : 34 gestational days; embryonic
length : 1.6mm(Earliest)
 THRESHOLD : Length 4-5mm ; GA 6.0-
6.5 wks ; MSD 13-18mm
 TAS: GA 8wks ; MSD 25mm.

13.  6 weeks : Flat disk changes to C-shaped embryo
 7-8 weeks: paddle shaped upper and lower limbs
 9th week : trunk elongates , extremities protrude ventrally and midgut
herniates into UC
 10th week : CRL 30-35mm – human appearing embryo , opposed limbs.

14. FETAL MEMBRANES AND PLACENTA
 Amnion normally
identified at 6-7 weeks ;
CRL 7mm
 Double bleb sign :
anatomic relationship of
amniotic sac + yolk sac
 CRL and amniotic sac inc
by 1mm/day
 So CRL of 12mm =
amniotic cavity with mean
dia of 12mm

15. FETAL MEMBRANES AND PLACENTA
 Amniotic membrane may or may
not be visible .
 Inability to visualize ≠ pregnancy
failure
 Presence of amnion = presence of
intra-uterine gestational sac
 Chorion may/may note be visible
 Low-level echoes may be seen

16. DETERMINING GESTATIONAL AGE
GSAC
 Most accurate time : first trimester
 First structure to be measured : GS(when no embryo or yolk sac is
visible) MSD is used
 5-11 weeks : 30 + MSD(mm) = GA in days
YOLK SAC
 YS – CA- embryo on TVS : 5.5weeks
 YS+ CA – CRL (too small to measure) : 6wks

17. DETERMINING GESTATIONAL AGE

18. DETERMINING GESTATIONAL AGE
CRL
 6-12 weeks : most accurate
 ± 4.7 days with 95% confidence
 GA(days) : 42 + CRL(mm)
 During end of first trimester , CRL
not accurate
 rapid fetal development
 flexion/extension positional
changes
 Hence BPD and FL

19. FIRST TRIMESTER COMPLICATIONS
 15% of clinically recognized pregnancies are spontaneously
Miscarried
 Vaginal spotting or frank bleeding – MC presentation
 Bleeding – implantation of the conceptus into the decidualized
endometrium.
 Threatened abortion : vaginal bleeding with long cervix + closed cervix+ live
embryo
 50% abort & 50% normal outcome
 Missed abortion : does not adequately describe pathophysiologic
changes and should be abandoned.
 Instead embryonic demise and blighted ovum

21. Threatened abortion
Absent GS
Normal uterus and
normal ET
1)No pregnancy
2)early IUP
3)Ectopic
Thickened ET
/irregularly
echogenic
RPOC/IUBLEED(heavy
bleeding)
DOPPLER FOR RETAINED TISSUE
DECIDUAL RXN
ECTOPIC
(heavy bleeding rare)
EARLY IUP
(HCG >disc level)
GS w/o embryo GS w/ embryo

23. Threatened
abortion
Absent GS GS w/o embryo GS w/ embryo

24. SAC WITHOUT EMBRYO
 Normal early IUP
 Abnormal IUP
 Pseudogestational sac – ectopic pregnancy
 IUS - within decidua & PseudoGS – within uterine cavity
 Hard to differentiate – f/u required to see yolk sac /embryo.

25. ABNORMAL SAC CRITERIA
NORMAL
 THRESHOLD(TVS): MSD 2-3mm ; GA :
4wks
 TAS: 5mm ; 5wks
ABNORMAL: TAS (TVS)
 No double decidual sac – MSD >10mm
 No Yolk Sac - MSD > 20mm (8mm)
 No embryo wd CA – MSD > 25mm
(16mm)

26. ABNORMAL SAC CRITERIA
GROWTH RATE
 Blighted ovum and anembryonic pregnancy : dvpt arrest before formn
of embryo /before it is detectable using current available equipment.
 Normal : 1.13 mm/day
 Abnormal: <0.6 mm/d

27. ABNORMAL SAC CRITERIA
TROPHOBLASTIC APPEARANCE
Abnormal chorio-decidual rxn
 Distorted sac shape
 <2mm thickness
 Weakly echogenic
 Absent DDS : MSD >10mm

28. ROLE OF DOPPLER
 Differentiate a pseudogestational sac from an intrauterine GS
 Flow around pseudo GS – absent or < 8cm/s PSV
 Flow around IU GS: high velocity with low resistance
 Not reliable as arterial flow with low resistance can also be seen with
pseudo-GS
 Doppler delivers more energy , hence restricted to prevent harmful
exposure to early embryo.

30. Threatened
abortion
Absent GS GS w/o embryo GS w/ embryo

31. DETECTING A SAC WITH EMBRYO
ABSENT CARDIAC ACTIVITY
 Usually poor prognosis
 THRESHOLD : 9mm(TAS) ; 5mm(TVS)
 If length of embryo <discriminatory level , Expectant management /
BhCG for normal IUP
Care to be taken:
 Highest transducer frequency
 M mode if available
 Real time clip/videotape documenting absent CA
 2nd independent observer to confirm the finding.

32. DETECTING A SAC WITH EMBRYO
CARDIAC ACTIVITY PRESENT
 Favourable prognosis
 CA + asymptomatic women >8weeks GA – risk of loss only 2-3%.

33. RISK FACTORS FOR EARLY PREGNANCY FAILURE
 GA – Inverse relation
 <6weeks : 7-24% chance
 >8weeks : 2%
 First trimester vaginal bleeding : 2-3X spont abortion
 HR
 Bradycardia
• 6.2 weeks : < 100bpm
• 6.3-7.0 wks : < 120bpm
 25% rate of demise
 a/w trisomy 18 and triploidy

34. RISK FACTORS FOR EARLY PREGNANCY FAILURE
 FIRST TRIMESTER OLIGOHYDRAMNIOS
 MSD – CRL < 5mm
 80-94% spont abortion despite normal CA

35. YOLK SAC EVALUATION
 Both the size and appearance of
the yolk sac should be
considered in early pregnancy.
SIZE
 Normal YS
 Max Diameter : 5-6mm at
10wks GA
 large yolk sac - increased risk for
spontaneous abortion.

36. YOLK SAC EVALUATION
APPEARANCE
 Abnormal shape
 Calcified
 Echogenic
 Double YS(vitelline duct
cyts)
a/w subsequent embryonic
demise

37. AMNION EVALUATION
 Not visualized normally till CRL 7mm
 Abnormal amnion dvpt
 Easy to see
 Thickness and echogenicity ~ yolk sac
 Amniotic cavity > CRL (normally both almost same size)
 Double bleb sign - impending or frank pregnancy failure
 Amnion without embryo ( usually embryo before the amnion)
• Empty amnion : MSD >16mm
• If MSD <16mm : correlate with b-hCG

38. AMNION EVALUATION
 Differentiating YS and amnion is usually difficult
 But any cystic structure > 6mm without live embryo – s/o pregnancy
failure

39. MATERNAL FACTORS
 Age > 34 years : 1.5 X
 Fibroids : 2 X
 Septate uterus – inadequate implantation
 Daughters of women who took diethylstilbestrol [DES

40. HCG LEVEL IN FIRST TRIMESTER
 GS growth and hCG relate to trophoblast function.
 HCG assay useful in equivocal cases and women at risk for recurrent
miscarriages – assess if pregnancy is progressing normally
 In abnormal IUP , hCG is disproportionately low
 Small intrauterine fluid collection with no DDS(TAS) or intra-decidual
sign (TVS) – to see if intrauterine findings are due to pseudoGS or early
IUP
 Ectopic pregnancy : absent IU-GS with hCG > discriminatory
levels(1000-2000mIU/ml)

41. ROLE OF DOPPLER IN PREDICTING PREGNANCY
OUTCOME
 Not routinely advocated – high energy
 Increased indices(RI ,PI)in uterine vessels : increased risk of spont
abortion
 By 6-12 weeks GA , indices within UA and spiral artery declines
 By 11 wks GA , increased UA RI – risk of IUGR and PIH

42. ECTOPIC PREGNANCY
 One of the leading cause of deaths
 1.4% of all pregnancies and approximately 15% of maternal deaths.
CLINICAL FEATURES
 Classical triad : pain + abnormal vaginal bleeding + palpable adnexal
mass( only 45% cases)
 Others : amenorrhea , adnexal tenderness , cervical motion
tenderness.
INCREASED RISK : previous tubal pregnancy , CS , PID , tubal recanalization
, IUCD and increased age

43. ECTOPIC PREGNANCY
SONOGRAPHIC DIAGNOSIS
 Pelvis USG and TVS – IOC
 Adnexal tenderness on TVS
 Initial examn: TAS through full bladder
 Look for extrauterine GS or hematoma
 FF in morrisons – sense of degree of blood loss(sense of urgency)
 TVS: assess uterus , ovaries and adnexa

44. ECTOPIC PREGNANCY
SPECIFIC FINDINGS
 Demonstration of IUP by TVS
 intradecidual sign and the double-decidual sign can be used to identify
an IUP
 DDS s`d be diff from decidual cast /pseudo GS(single decidual layer)
 Demo of LIVE EMBRYO IN ADNEXA

47. ECTOPIC PREGNANCY
NON-SPECFIC FINDINGS
 SERUM hCG correlation when sonography is non-specific
 Negative b hCG rules out live pregnancy
 B hCG positive by 23 days of GA
 THRESHOLD : TAS : >1800 ; TVS : 500-1000mIU/ml
 But If the β-hCG level is below the threshold level, the sonogram may
still identify an ectopic pregnancy.
 Normally B hCG doubles in 2 days ; hence serial quantitiative assay will
be helpful as dead or dying gestation have a falling β-hCG level.

48. ECTOPIC PREGNANCY
 Pts with ectopic has slower rise in B hCG .
 An adnexal mass : ectopic pregnancy , hemorrhagic corpus luteum cyst,
endometriosis, and abscess. Hence not diagnostic.
 But pelvis mass+ no e/o IUP + positive B hCG = ectopic mostly
 TUBAL RING : concentric ring created by the trophoblast of the ectopic
pregnancy surrounding the chorionic sac.
 Diff from corpus luteal cyst : cyst is in eccentric position , hypoechoic
compared to ovarian parenchyma (tubal ring > ovarian parenchyma)

49. ECTOPIC PREGNANCY
 Useful in detecting free pelvic fluid.
 HP or blood in cul-desac + no IUP : s/o ectopic
 Small amout of NON-ECHOGENIC is seen in normal pts.
 presence or the amount of intraperitoneal fluid was not a reliable
indicator of rupture.
 Intraperitoneal fluid is possible if the blood escapes through the
fimbriated end of the intact fallopian tube.

52. ECTOPIC PREGNANCY
HETEROTOPIC GESTATION
 Risk : IVF /ovulation induction
 Sonography : live embryo in adnexa with IU GS

53. HETEROTOPIC PREGNANCY

54. MULTIPLE PREGNANCY

55. MULTIPLE PREGNANCY
SONOGRAPHIC DETERMINATION
 Chorionicity can be determined with high reliability in the first trimester with
accuracy of 98% to 100%
 6-9 WEEKS : MEMBRANE THICKNESS for chorionicity and number of yolk sac
for amnionicity
 Membrane thicker > 2mm : dichrionic gestn
 If its thin and imperceptible – monochorionic gestation.
 One yolk sac with 2 embryos : monoamniotic gestation
 2 YS + 2 embryos +/- intervening memebrane : diamniotic gestation

57. DETECTING FETAL ANOMALIES
 IN > 50% CASES , cause is unknown
 MC identifiable cause : chromosomal aberration
 < 5 weeks exposure : all or none ( either die / normal)
 5-10 weeks (organogenesis) : affects organ dvpt

58. DEVELOPMENT PITFALLS
 In a developing embryo , normal
structures may be interpreted
as abnormal
DEVELOPING RHOMBENCEPHALON
 In posterior cranium between 7-9
weeks
 Seen as a cystic area
 Eventually develop as 4th ventricle ,
brain stem and cerebellum.
 Can be confused with
hydrocephalus/dandy walker
malformation

59. DEVELOPMENT PITFALLS
PROMINENCE OF FETAL
UMBILICAL CORD INSERTION
SITE
 @ 8TH WK GA: physiological
herniation of bowel into
base of umbilical cord
creates a focal mass
 Size ≤ 7m , prominent at 9-
10 weeks , resolve by end of
11th week , not seen once
CRL >45mm.

60. DIAGNOSING ANOMALIES
 By 10 weeks’ GA, the fetal cranium, brain, neck, trunk, and
extremities can be visualized, and gross anomalies can be
detected in the first trimester.
ANENCEPHALY
 Absence of dvpt of cranium with dystrophic brain tissue
 Fetal head has an irregular contour /no calcified cranium with brain
tissue extending beyond the usual location.

62. DIAGNOSING ANOMALIES
ENCEPHALOCOELE
 defects in the
cranium through
which intracranial
contents herniate
outside the skull,

63. DIAGNOSING ANOMALIES
HOLOPROSENCEPHALY
 failure of cleavage of the
prosencephalon into the
cerebral hemispheres
 large central cystic space
and the falx and choroid
plexus are absent
 a/w trisomy 13

64. DIAGNOSING ANOMALIES
CYSTIC HYGROMA/LYMPHANGIECTASIA
 large cystic spaces behind the fetal head, neck, and trunk
 Trisomy 13,18 , 21 and turners syndrome
 Can extend down the trunk appearing as halo or cofined to posterior
fetal neck

65. DIAGNOSING ANOMALIES

66. DIAGNOSING ANOMALIES
OMPHALOCELE AND GASTROSCHISIS
 Diff rom physiological bowel herniation
 Mass beyond 12 wks GA
 Size > 7mm
 Ompahlocele mass has a smooth and rounded contour due to
peritoneal covering.
 Gastroschisis: irregular contour as protruding loops not contained by
membrane

67. GASTROSCHISIS

68. OMPHALOCELE

69. DIAGNOSING ANOMALIES
AMNIOTIC BAND SYNDROME
 entrapment of various fetal parts from a disrupted amnion.
 Ventral wall defect + encephalocele + limb amputation

70. SCREENING FOR ANEUPLOIDY
FETAL NUCHAL TRANSLUCENY
 Single most powerful marker for diff downs syndrome from euploidy.
 Normal subcutaneous fluid-filled space etween the back of the fetal
neck and the overlying skin
 Normally very small , increased in downs syndrome.

71. SCREENING FOR ANEUPLOIDY

72. SCREENING FOR ANEUPLOIDY
 The fetus should be imaged in the midsagittal plane, ideally with the fetal spine down.
 Adequate magnified so that only the fetal head, neck, and upper thorax fill the viewable
 area.
 The fetal neck should be neutral, with care being taken toavoid measurements in the
hyperflexed or hyperextendedpositions.
 The skin at the fetal back should be clearly differentiated from the underlying amniotic
membrane, either by visualizing separate echogenic lines or by noting that the skin line
moves with the fetus.
 Measurement calipers should be placed on the inner borders of the echolucent space and
should be perpendicular to the long axis of the fetus (see Fig. 3–1).
 Ultrasound and transducer settings should be optimized to ensure clarity of the image and
of the borders of the nuchal space in particular. This may require transvaginal sonography
in certain situations.

73. NUCHAL TRANSLUCENCY
 a value of less than ~2.2-2.8 mm in thickness is not associated with
increased risk
 Nuchal translucency cannot be adequately assessed if there is:
 unfavourable fetal lie
 unfavourable gestational age: CRL <45 or >84 mm
 Mean nuchal translucency measurements increase by 15% to 20% each week
from 10 to 14 weeks’ gestation.
 Hence no single value but preferably 95th percentile for a particular
gestational age.

74. SCREENING FOR ANEUPLOIDY
NUCHAL TRANSLUCENCY WITH SERUM MARKERS

75. SCREENING FOR ANEUPLOIDY
NASAL BONE SONOGRAPHY
 a/w downs syn.
 The fetal nasal bones could not be
visualized in 73% of Down syndrome
fetuses
TECHNIQUE
 Mid-sagittal plane
 The fetal spine should be posterior,
with slight neck flexion.
 Two echogenic lines at the fetal nose
profile should be visualized
(nasal skin and bone)

76. SCREENING FOR ANEUPLOIDY
DUCTUS VENOUS SONOGRAPHY
 adjunctive test for fetal aneuploidy screening.
 Normal : forward triphasic pulsatile DV flow
 Abnormal : reversed flow at the time of atrial contraction
 a/w : aneuploidy and fetal cardiac malformn
 This could be used to either improve the detection rate or
alternatively to reduce the false-positive rate.
 PITFALL : contamination of the waveform from neighboring
Vessels.

77. SCREENING FOR ANEUPLOIDY

78. SCREENING FOR ANEUPLOIDY
TRICUSPID REGURGITATION EVALUATION
 fetus should be oriented so that the chest wall is anterior
 the fetal heart should be insonated parallel to the ventricular septum
 3mm gate at tricuspid valve
 regurgitant jet of at least 60 cm/sec is noted extending to over half of
systole : significant

79. FETAL MEGACYSTIS
 Unusually large bladder in a fetus.
 Bladder diameter : > 7mm in 1st trimester
 if the longitudinal bladder diameter of 7-15 mm there is a risk of a
chromosomal defects is estimated at ~25% 4
 if the bladder diameter is >15 mm the risk of chromosomal defects is
estimated at ~10% (usually obstructive uropathy )
 May be a/w oligohydramnios/renal anomalies

81. SCREENING
FOR
ANEUPLOIDY

82. FIRST TRIMESTER MASSES
OVARIAN MASSES
 MC : corpus luteum cyst
 Corpus luteum
 Secretes prog to support pregnancy
 <5cm in diameter
 Thick walled cyst with circumferential vascular flow

83. OVARIAN MASSES
CL CYST
 Occasionally size > 10cm
 Internal septation and echogenic debris – 2o H’age
 extremely thick cyst wall and septations
 Decrease in size on follow up at 16-18 wks(diff from pathological cysts)
 Though not all regress
 Adnexal cystic masses < 5 cm in diameter in the first trimester are usually
follicular or corpus luteum cysts and almost always resolve spontaneously.

85. UTERINE MASSES
FIBROIDS
 common pelvic mass often identified during pregnancy
 Localized pain and tenderness.
 Most do not change in size , though some enlarge rapidly – resulting in
infarction and necrosis
 USG: solid, often hypoechoic uterine masses with areas of calcification
and may have cystic , avascular area related to necrosis.
 Increased spontaneous loss rate in early singleton pregnancies