First trimester ultrasound

FIRST TRIMESTER

ULTRASOUNDDr Roshan Valentine

PG Resident Dept od RadioDiagnosis

St Johns Medical College, bangalore

INTRODUCTION

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

INTRODUCTIONWHY 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

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)

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)

IDENTIFYING THE GSAC

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

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

INDENTIFYING EMBRYO AND CARDIAC ACTIVITY

EMBRYONIC DISK : Subtle focal thickening along the

periphery of yolk sac. THRESHOLD : 5-6 wks; MSD 5-12mmCARDIAC 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.

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.

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

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

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 daysYOLK SAC YS – CA- embryo on TVS : 5.5weeks YS+ CA – CRL (too small to measure) : 6wks



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

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 pathophysiologicchanges and should be abandoned. Instead embryonic demise and blighted ovum

Threatened abortion

Absent GS

Normal uterus and normal ET

Thickened ET /irregularly echogenic

GS w/o embryo GS w/ embryo

Threatened abortion

Absent GS GS w/o embryo GS w/ embryo

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.

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)


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


TROPHOBLASTIC APPEARANCEAbnormal chorio-decidual rxn

Distorted sac shape <2mm thickness Weakly echogenic Absent DDS : MSD >10mm

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.

Threatened abortion

Absent GS GS w/o embryo GS w/ embryo

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 IUPCare to be taken: Highest transducer frequency M mode if available Real time clip/videotape documenting absent CA 2nd independent observer to confirm the finding.

DETECTING A SAC WITH EMBRYO

CARDIAC ACTIVITY PRESENT Favourable prognosis CA + asymptomatic women >8weeks GA – risk of loss only 2-3%.

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

RISK FACTORS FOR EARLY PREGNANCY FAILURE

FIRST TRIMESTER OLIGOHYDRAMNIOS MSD – CRL < 5mm 80-94% spont abortion despite normal CA

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.

YOLK SAC EVALUATION

APPEARANCE Abnormal shape Calcified Echogenic Double YS(vitelline duct

cyts)a/w subsequent embryonic demise

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

AMNION EVALUATION

Differentiating YS and amnion is usually difficult But any cystic structure > 6mm without live embryo – s/o pregnancy

failure

MATERNAL FACTORS

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

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)

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

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

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

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

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.

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)

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.

ECTOPIC PREGNANCY

HETEROTOPIC GESTATION Risk : IVF /ovulation induction Sonography : live embryo in adnexa with IU GS

HETEROTOPIC PREGNANCY

MULTIPLE PREGNANCY

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

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

DEVELOPMENT PITFALLS

In a developing embryo , normal structures may be interpreted

as abnormalDEVELOPING 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

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.

DIAGNOSING ANOMALIES

By 10 weeks’ GA, the fetal cranium, brain, neck, trunk, andextremities can be visualized, and gross anomalies can bedetected 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.


ENCEPHALOCOELE defects in the

cranium through which intracranial contents herniate outside the skull,


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


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



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

GASTROSCHISIS

OMPHALOCELE


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

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.



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.

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.

http://radiopaedia.org/articles/missing?article%5Btitle%5D=fetal-lie


NUCHAL TRANSLUCENCY WITH SERUM MARKERS


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)


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 neighboringVessels.



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

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


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

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.

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

First trimester ultrasound

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