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Published on : Aug 02, 2021 | Views : 5468 | Downloads : 31

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FIRST TRIMESTER ULTRASOUND Dr Roshan Valentine PG Resident Dept od RadioDiagnosis St Johns Medical College, bangalore
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INTRODUCTION FIRST TRIMESTER Most critical and tenuous period of human dvpt Single cell into recognizable human being Till 12 weeks
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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
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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)
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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)
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IDENTIFYING THE GSAC
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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
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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
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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.
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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.
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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
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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
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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
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DETERMINING GESTATIONAL AGE
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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
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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
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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
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Threatened abortion Absent GS GS w/o embryo GS w/ embryo
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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.
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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)
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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
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ABNORMAL SAC CRITERIA TROPHOBLASTIC APPEARANCE Abnormal chorio-decidual rxn Distorted sac shape <2mm thickness Weakly echogenic Absent DDS : MSD >10mm
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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.
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Threatened abortion Absent GS GS w/o embryo GS w/ embryo
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DETECTING A SAC WITH EMBRYO ABSENT CARDIAC ACTIVITY Usually poor prognosis THRESHOLD : 9mm(TAS) ; 5mm(TVS) If length of embryo
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DETECTING A SAC WITH EMBRYO CARDIAC ACTIVITY PRESENT Favourable prognosis CA + asymptomatic women >8weeks GA – risk of loss only 2-3%.
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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
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RISK FACTORS FOR EARLY PREGNANCY FAILURE FIRST TRIMESTER OLIGOHYDRAMNIOS MSD – CRL < 5mm 80-94% spont abortion despite normal CA
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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.
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YOLK SAC EVALUATION APPEARANCE Abnormal shape Calcified Echogenic Double YS(vitelline duct cyts) a/w subsequent embryonic demise
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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
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AMNION EVALUATION Differentiating YS and amnion is usually difficult But any cystic structure > 6mm without live embryo – s/o pregnancy failure
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MATERNAL FACTORS Age > 34 years : 1.5 X Fibroids : 2 X Septate uterus – inadequate implantation Daughters of women who took diethylstilbestrol [DES
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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)
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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
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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
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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
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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
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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.
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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)
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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.
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ECTOPIC PREGNANCY HETEROTOPIC GESTATION Risk : IVF /ovulation induction Sonography : live embryo in adnexa with IU GS
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HETEROTOPIC PREGNANCY
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MULTIPLE PREGNANCY
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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
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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
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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
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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.
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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.
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DIAGNOSING ANOMALIES ENCEPHALOCOELE defects in the cranium through which intracranial contents herniate outside the skull,
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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
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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
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DIAGNOSING ANOMALIES
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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
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GASTROSCHISIS
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OMPHALOCELE
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DIAGNOSING ANOMALIES AMNIOTIC BAND SYNDROME entrapment of various fetal parts from a disrupted amnion. Ventral wall defect + encephalocele + limb amputation
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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.
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SCREENING FOR ANEUPLOIDY
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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.
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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.
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SCREENING FOR ANEUPLOIDY NUCHAL TRANSLUCENCY WITH SERUM MARKERS
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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)
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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.
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SCREENING FOR ANEUPLOIDY
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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
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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
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SCREENING FOR ANEUPLOIDY
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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
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OVARIAN MASSES H’age CL CYST Occasionally size > 10cm Internal septation and echogenic debris – 2o 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.
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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
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