Role of TVS in Early

Pregnancy

Poonam Loomba,M.D.

Nothing to disclose

Introduction

Advancement in TVS has revolutionised

the management of early pregnancy.

Care providers can utilize this noninvasive

tool for a better understanding of the

embryonic development and thus improve

their clinical as well as counselling skills.

Objectives 1. Highlight embryonic developmental features.

2. Application of TVS in management of early pregnancy failure ,ectopic pregnancy and multiple pregnancies.

3. Placental pathologies on USG.

4. Identify and evaluate first trimester markers of aneuploidy

5. 3D and 4D USG in first trimester

6.Markers for Preeclampsia through TVS in Early pregnancy.

Gestation sac The first sonographic evidence of

pregnancy is the gestational sac within the thickened decidua.

This sac, represents the exocoelomic fluid of blastocyst surrounded by an echogenic ring that represents trophoblasts and decidual reaction.

The hyperechoic rim should be atleast 2mm thick and its echogenicity should exceed the myometrial echoes

With TVS the size threshold for sac detection is 2 to 3mm corresponding to between 4 weeks 1 day to 4 weeks 3 days gestation

The loss rate at this stage is 11.5%

Position of GSAC

Normal position is in the mid to upper uterus

Intradecidual sign :as the sac implants into the decidualized endometrium it should be adjacent to linear central cavity echo complex without displacing this hyperechoic anatomic landmark

Double decidual sac sign: as the sac enlarges it impresses and deforms the central cavity echo complex giving appearance of DDSS .Visible when MSD is 10mm.

DDSIntradecidual Sac Sign

Gestation Sac

Identifying yolk sac

The yolk sac(embryologically secondary yolk sac) is the first structure seen within the gestational sac and, when seen, confirms an intrauterine pregnancy.

The yolk sac is seen by transvaginal ultrasound when the mean gestational sac diameter is

5 to 6 mm(5 weeks) and should always be visualized when the mean gestational sac diameter is greater than or equal to 8 mm.(5.5 weeks)

Yolk sac Yolk sac is normally

spherical in shape with a well defined echogenic periphery and a sonoluscent centre

Size:steadily increases from 5 to 10 weeks to a max of 5 to 6mm(corresp to CRL 30 to 45 mm)

As GA advances it seperates and detatches from the embryo,diameter decreases and becomes irregular

Not visualized on tvs by end of first trimester

Identifying the embryo

The embryo can be identified by

transvaginal ultrasound when as small

as 1 to 2 mm in length(corresponding

to 5 to 6 weeks GA and MSD between

5 to 12mm)

Its seen as a focal area of thickening

along the periphery of yolk sac

At 5 to 7 weeks, both the embryo and

gestational sac should grow by 1 mm

daily.

Embryo

Multiples of 2

2mm sac 2mm thick

6mm yolk sac

8mmsac

2mm embryo ,6 to

12mm g sac

6mm embryo ,14 to

18 mm g sac

4w ga

6wga

6w ga

Cardiac activity at

6w ga

Viability

Cardiac activity immediately adjacent to the yolk sac indicates a live embryo but may not be seen until the embryo measures 5 mm.(corresponding to GA of 6 .0 to 6.5 weeks and MSD 13-18mm on tvs and MSD 25mm and GA 8 weeks on TAS)

From 5.5 to 6.5 weeks, an embryonic heart rate of less than 100 beats per minute is normal.

During the following 3 weeks, there is a rapid increase up to 180 beats per minute.

Normal Heart Rate

5.5 to 6 wks : 1. 100-125/min

2. <100/min

3 100 -115/min

8wks and above

1. 137-144/min

2 144-159/min

3 140 -160/min

Transformation in the structure

of embryo During 6th week,with ventral folding of

cranial and caudal ends of embryo it changes shape from a flat disc to a 3d C shaped structure

Brain and head become prominent as rostral neuropore closes and caudal neuropore elongates and curves into a tail

Despite the extra amniotic location of yolk sac initially it remains attatched to the embryo via an omphalomesentric duct

• By 7th to 8th week limb buds evolve

• By 9th week extremities protrude ventrally

trunk elongates and straightens and

midgut herniation into umbilical cord

becomes more prominent

• By 10 th week at embryo length 30mm to

35 mm human appearing embryo is seen

Measuring CRL

CRL measurements can be carried out transabdominally or transvaginally.

A midline sagittal section of the whole embryo or fetus should be obtained, ideally with the embryo or fetus oriented horizontally on the screen.

An image should be magnified sufficiently to fill most of the width of the ultrasound screen, so that the measurement line between crown and rump is at about 90 degrees to the ultrasound beam

Electronic linear calipers should be used to measure the fetus in a neutral position (i.e. neither flexed nor hyperextended. )

Care must be taken to avoid inclusion of structures such as the yolk sac.

In order to ensure that the fetus is not flexed, amniotic fluid should

be visible between the fetal chin and chest

• Upto and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ± 5–7 days

• The measurement used for dating should be the mean of three discrete CRL measurements when possible and should be obtained in a true midsagittal plane, with the genital tubercle and fetal spine longitudinally in view and the maximum length from cranium to caudal rump measured as a straight line

• Mean sac diameter measurements are not recommended for estimating the due date. Beyond measurements of 84 mm (corresponding to approximately 14 0/7 weeks of gestation), the accuracy of the CRL to estimate gestational age decreases, and in these cases, other second-trimester biometric parameters should be used for dating

Trophoblastic appearance

Distorted sac shape

thin<2mm

weakly echogenic

and irregular choriodecidual reaction

Absence of DDSC when MSD>10 mm

Presence of chorionic bump(irregular convex bulge arising from choriodecidual surface and protruding into GSAC)

Abnormal gestation sacs

Transvaginal sonographic

diagnosis of a blighted ovum

is certain when the mean

gestational sac diameter

exceeds 8mm without a yolk

sac or when the mean

gestational sac diameter

exceeds 16 mm without

an embryo

Transabdominally, a

gestational sac greater than

20 mm without a yolk sac or

25 mm without an embryo is

diagnostic of a blighted ovum

Yolk sac abnormalities

Enlarged (5 to 6 mm)

seen in IDDM

or abnormally shaped

(crenellated) yolk sac,

Calcified

Echogenic

Double yolk sac

Growth Rate

MSD increases by 1.13mm/day in

normal gestation and abnormal sac

growth is when MSD fails to grow by at

least .6mm/day

CARDIAC ACTIVITY

ABSENT Sonographic diagnosis

of embryonic demise can be made when there is no cardiac activity in an embryo greater than 5mm by transvaginal ultrasound or 9 mm by abdominal ultrasound

(If cardiac activity is present in at 8 weeks the risk of loss is only 2 to 3%)

Predictors of early pregnancy

loss

Heart rate-

Persistent bradycardia (heart rate less

than 100BPM before 6.2 weeks and less

than 120 between 6.3 and 7 weeks of

gestation,)

Bradycardia associated with triploidy

and trisomy 18

Tachycardia associated with trisomy 13

and turners syndrome

Intrauterine blood Presence of subchorionic blood

increases the abortion rate to 8 %

Various sites are:

retroplacental

Preplacental

Marginal

Subamniotic

On USG it appears initially as a

hypoechoic area adjacent to GSAC

which later becomes hypo/anechoic

Subchorionic haemorrhage

Small sac size growth delay

a small sac size relative to the embryo

(difference of less than 5 mm between

gestational sac and crown/rump

length) indicates early oligohydramnios

and increased rate of abortion

Amnion abnormailities

Membrane is easily visualized

Thickness and echogenicity similar to

yolk sac

Enlarged yolk sac in relation to

CRL(normal preg diff 1mm in CRL and

amniotic cavity diameter)

Double bleb sign

Role of doppler in predicting

poor pregnancy outcome

Elevated resistance in uterine and

subchorionic vessels increase abortion

rate

Increased corpus luteal RI- increased

preg loss

Multiple pregnancies

DIAGNOSING MULTIPLE

PREGNANCY

Always begin a scan with a complete

imaging sweep of the uterus and count

the number of fetus, determine their

presentation,document their site and

chorionicity

First trimester evaluation is the best time

to determine the chorionicity in multiple

gestation

Chorionicity assessment

(before 10 weeks)

Number of Yolk Sacs

Number of GSAC

Number of amniotic sacs in chorionic

cavity

After 10 weeks

Sex discordance

No of distinct placenta

Twin peak/lambda sign-results from

echodense chorionic villi between the two

layers of chorion at its origin from the

placenta.(100% PPV for DC placentation)

T sign:MCDA placentation

Epsilon sign:TCTA placentation

Membrane thickness:cutoff 2mm

Twin Peak or lambda sign

Ectopic pregnancy

Failure to detect an intrauterine

gestational sac by transvaginal

ultrasound when the beta-hCG value

exceeds a discriminatory level (1000 to

2000 mIU/ml) indicates an increased risk

for ectopic pregnancy.

With a complex adnexal mass or a tubal

ring, the probability of ectopic pregnancy is

high, while a live extrauterine embryo is

diagnostic of an ectopic .

USG features of ectopic

pregnancy The sonographic appearance of an

ectopic is varied ranging from

simple adnexal cyst,

complex adnexal mass,

tubal ring, (ring on fire app)

free fluid in the adnexa-cul de sac,

a live extrauterine fetus,

or an empty uterus with no other

sonographic findings

USG features for ectopic

Negative sonographic signs-intrauterine pregnancy

False negative sonographic sign-intrauterine Gsac

Indirect positive sign-empty uterus and the discriminatory zone and free pelvic and abdominal fluid

Direct positive sign-adnexal pregnancy,tubal or adnexal ring,complex or solid mass

Placental pathologies

Echo rich trophoblastic tissue-diffuse small cystic structures without gestational components.

Snowstorm appearance

Theca lutein cysts in adnexal region(soap bubble or spoke wheel app of ovaries)

Molar pregnancy

On doppler:high velocity and low

resistance to flow in uterine artery

Invasive mole:in addition to central

uterine lesion myometrial invasion

present

Choriocarcinoma:hetrogenous mass

enlarging the uterus due to areas of

necrosis and hemorrhage

Screening for chromosomal

anamolies using NT involves:

1 . Carrying out the ultrasound examination by appropriately trained sonographers.

2.Measurement of maternal serum free β-hCG and PAPP-A by laboratories that can demonstrate good quality assurance performance.

3. A risk calculation programme that uses an algorithm based on scientific evidence.

4 Appropriate counselling of the parents.

Nuchal Translucency

Needs high standard of knowledge and

expertise.

The machine should have a good

resolution ,video loop function .

In 95% of cases it can be measured by

TAS ..in rest by TVS.

Minimum 80-100 scans needed for good

results.

PROTOCOL FOR

MEASURING NT Fetus in neutral position.

Mid sagittal plane with face and chest occupying full screen

11 to 13+ 6 weeks

The magnification should be such that each increment in the distance between calipers should be 0.1mm

NT

NT

Measurements should be taken with the inner border of the horizontal line of the callipers placed ON the line that defines the nuchal translucency thickness -the crossbar of the calliper should be such that it is hardly visible as it merges with the white line of the border, not in the nuchal fluid.

In magnifying the image (pre or post freeze zoom) it is important to turn the gain down. This avoids the mistake of placing the calliper on the fuzzy edge of the line which causes an underestimate of the nuchalmeasurement.

During the scan more than one measurement must be taken and the maximum one that meets all the above criteria should be recorded in the database.

.

The umbilical cord may be round the

fetal neck in about 5% to 10% of cases

and this finding may produce a falsely

increased NT.

In such cases, the measurements of NT

above and below the cord are different

and, in the calculation of risk, it is more

appropriate to use the lowest of the two

measurements

NTT at 14 wks

Causes of increased NT

Aneuplodies

Abnormalities of heart and great arteries

Amnion rupture

Diaphragmatic hernia

Skeletal dysplasias

Achondrogenesis

Hypoplasia of lymhatics as in Turner syndrome.

Anaemia

Congenital infections

First trimester screening

NT

Serum free beta hcg

PAPP-A

Calculate risk score by adding maternal

age and previous history

Single cutoff not appropriate.Rather 95th

percentile of CRL

NASAL BONE

EVALUATION In a high proportion of fetuses with trisomy 21 and

other chromosomal abnormalities the nasal bone is hypoplastic or not visible at 11-13 weeks' gestation.

Assessment of the nasal bone at 11-13 weeks improves the performance of combined screening for trisomy 21 by maternal age, fetal nuchaltranslucency (NT) and serum biochemistry.

The difficulty is when the gestation is 11 weeks or the beginning of the 12th week and the nasal bone is absent but the NT, the other ultrasound markers and the serum biochemistry are normal.

PROTOCOL

The gestational period must be 11 to 13 weeks and six days.

The magnification of the image should be such that the fetal head and thorax occupy the whole image.

A mid-sagittal view of the face should be obtained.

This is defined by the presence of the echogenic tip of the nose and rectangular shape of the palate anteriorly, the translucent diencephalon in the centre and the nuchal membrane posteriorly.

Minor deviations from the exact midline plane would cause non-visualization of the tip of the nose and visibility of the zygomatic process of the maxilla.

How to measure NB

The ultrasound transducer should be held parallel to the direction of the nose and should be gently tilted from side to side to ensure that the nasal bone is seen separate from the nasal skin.

The echogenicity of the nasal bone should be greater that the skin overlying it.

In this respect, the correct view of the nasal bone should demonstrate three distinct lines: the first two lines, which are proximal to the forehead, are horizontal and parallel to each other, resembling an "equal sign".

The top line represents the skin and bottom one, which is thicker and more echogenic than the overlying skin, represents the nasal bone.

A third line, almost in continuity with the skin, but at a higher level, represents the tip of the nose.

When the nasal bone line appears as a thin line,

less echogenic than the overlying skin, it suggests

that the nasal bone is not yet ossified, and it is

therefore classified as being absent.

DUCTUS VENOSUS FLOW

Increased impedance to flow in the fetal ductus venosus at 11-13 weeks’ gestation, is associated fetal aneuploidies, cardiac defects and other adverse pregnancy outcomes.

Most studies examining ductus venosus flow have classified the waveforms as normal, when the a-wave observed during atrial contraction is positive, or abnormal, when the a-wave is absent or reversed.

The preferred alternative in the estimation of patient-specific risks for pregnancy complications is measurement of the pulsatility index for veins (PIV) as a continuous variable.

Inclusion of ductus venosus blood flow in first-trimester combined screening improves the detection rate for trisomy 21 from about 90% to 95% for a false positive rate of 3%.

Assessment of ductus venosus flow need not be carried out in all pregnancies undergoing routine first-trimester combined screening.

Such examination could be reserved for the 15% of the total population with an intermediate risk (between 1 in 51 and 1 in 1000) after combined testing.

PROTOCOL The gestational period must be 11 to 13 weeks and

six days.

The examination should be undertaken during fetal quiescence.

The magnification of the image should be such that the fetal thorax and abdomen occupy the whole image.

A right ventral mid-sagittal view of the fetal trunk should be obtained and color flow mapping should be undertaken to demonstrate the umbilical vein, ductus venosus and fetal heart.

The pulsed Doppler sample volume should be small (0.5-1.0 mm) to avoid contamination from the adjacent veins, and it should be placed in the yellowish aliasing area.

The insonation angle should be less than 30 degrees.

The filter should be set at a low frequency (50-

70 Hz) so that the a-wave is not obscured.

The sweep speed should be high (2-3 cm/s) so

that the waveforms are spread allowing better

assessment of the a-wave.

When these criteria are satisfied, it is possible to

assess the a-wave and determine qualitatively

whether the flow is positive, absent or reversed.

The ductus venosus PIV is measured by the

machine after manual tracing of the outline of

the waveform.

TRICUSPID FLOW

Tricuspid regurgitation at 11-13 weeks’ gestation is a common finding in fetuses with trisomies 21, 18 and 13 and in those with major cardiac defects.

Tricuspid regurgitation is found in about 1% of euploid fetuses, in 55% of fetuses with trisomy 21 and in one third of fetuses with trisomy 18 and trisomy 13.

Inclusion of tricuspid blood flow in first-trimester combined screening improves the detection rate for trisomy 21 from about 90% to 95% for a false positive rate of 3%.

Assessment of tricuspid flow need not be carried out in all pregnancies undergoing routine first-trimester combined screening. Such examination could be reserved for the 15% of the total population with an intermediate risk (between 1 in 51 and 1 in 1000) after combined testing.

PROTOCOL

The gestational period must be 11 to 13 weeks and six days.

The magnification of the image should be such that the fetal thorax occupies most of the image.

An apical four-chamber view of the fetal heart should be obtained.

A pulsed-wave Doppler sample volume of 2.0 to 3.0 mm should be positioned across the tricuspid valve so that the angle to the direction of flow is less than 30 degrees from the direction of the inter-ventricular septum.

Tricuspid rehurgitation

Tricuspid regurgitation is diagnosed if it is found during at least half of the systole and with a velocity of over 60 cm/s, since aortic or pulmonary arterial blood flow at this gestation can produce a maximum velocity of 50 cm/s.

The sweep speed should be high (2-3 cm/s) so that the waveforms are widely spread for better assessment.

The tricuspid valve could be insufficient in one or more of its three cusps, and therefore the sample volume should be placed across the valve at least three times, in an attempt to interrogate the complete valve.

Diagnosing

anomalies(excluding nt) Anencephaly

Large encephalocoels

Holoprosencephaly

Cystic hygroma

Omphalocoel/gastrochisis(size of

protruding ant abd mass>7mm

and persistence beyond 12weeks)

Amniotic band syndrome

Conjoined twins

USG Parameters for detection of

downs syndrome in first trimester

Nuchal translucency

Nasal bone(absent 69% cases)

FMF angle

Ductus venosus flow velocity waveform

Tricuspid regurgitation

Fetal heart rate(tachycardia)

Underdevelopment of maxilla(seen in 50% cases)

Short ear length

Short femur and humerus during 11-16 weeks at 6 day scan window

USG Parameters for detection

of Trisomy 13 in first trimester

Nuchal translucency

Nasal bone(absent 40% cases)

Fetal facial angle(increased 45% cases)

Ductusvenosus

Tricuspid regurgitation

Megacystis(urinary bladder length >7mm)20%

Fetal tachycardia

Trisomy 18

Trisomy 18: absent nasal bone 50%

cases,single umbilical artery(7 fold

),fetal bradycardia

Turners syndrome:choroid plexus

cyst(75% cases)

PREECLAMPSIA

SCREENING There is now evidence that a combination of

maternal demographic characteristics, including medical and obstetric history, uterine artery pulsatility index (PI), mean arterial pressure (MAP) and maternal serum pregnancy associated plasma protein-A (PAPP-A) and placental growth factor (PlGF) at 11-13 weeks' gestation can identify a high proportion of pregnancies at high-risk for PE.

Such early identification of the high-risk group for PE is important because the risk may be substantially reduced by the prophylactic use of low-dose aspirin starting from 11-13 weeks.

PROTOCOL FOR

MEASURING UTERINE A PI

The gestational age must be between 11 weeks and 13 weeks and six days.

Sagittal section of the uterus must be obtained and the cervical canal and internal cervical os identified.

Subsequently, the transducer must be gently tilted from side to side and then colour flow mapping should be used to identify each uterine artery along the side of the cervix and uterus at the level of the internal os.

Pulsed wave Doppler should be used with the sampling gate set at 2 mm to cover the whole vessel and ensuring that the angle of insonation is less than 30º. When three similar consecutive waveforms are obtained the PI must be measured and the mean PI of the left and right arteries be calculated.

3D 4d

Main advantages are working on the neurological system,facial anamolies,anamolies of skeleton esp limbs,fetal echocardiography

3DUS is also being considered for measurement of NT and nasal bone

Also useful in detailed evaluation of conjoined twins

4DUS allows fetal motoral and behavioural pattern assessment

Role of 3d 4d ultrasound in first

trimester

Allows imaging from volume sonographic data than conventional planar data

Not a substitution but increasingly useful as a complementary technique

3DUS allows better identification of the anatomic structures and a detailed fetal anatomy esp in cases with increase of chromosomal anomaly risk

Factors affecting interpretation

Imaging results on TVS are operator dependant

Minimize visual acuity with appropriate magnification

Myometrial heterogeneity,myomas and IUD can inhibit early pregnancy structures

Equipment age ,maintenance and variability

Multiple gestation or small gestation sacs

Unusually large sac or growth restricted embryo

Serial ultrasound scans are suggested with follow up for reassurance and better counselling

Thank you

Through our efforts at continued learning and improvising technologies we

can thus help build happy families