Presentation1.pptx, ultrasound examination of the 1st trimester pregnancy.
ULTRASOUND EXAMINATION OF THE 1ST TRIMESTER.
Dr/ ABD ALLAH NAZEER. MD.
FIRST TRIMESTER ULTRASOUND - Normal
1ST TRIMESTER ULTRASOUND PROTOCOL
ROLE OF ULTRASOUND
Ultrasound is essentially used for assessing gestational age, current viability and
maternal wellbeing. Ultrasound is a valuable diagnostic tool in assessing the
Unsure of Dates
Exclude an ectopic pregnancy
Maternal past history
Nuchal Translucency (11-14 weeks : CRL 45-84mm)
Parity (Miscarriage, Termination of Pregnancy (T.O.P))
Date of Last Menstrual Period
Other pregnancy History
EQUIPMENT SELECTION AND TECHNIQUE
Modern ultrasound unit
Curved linear probe approx 3-7 MHz depending upon maternal factors
Transvaginal probe approx 5-9 MHz (Use of non-latex cover if
Ensure patient comfort and privacy.
Warm gel, clean towels etc
Select "Obstetric" preset for appropriate power levels and
Use a curvilinear probe (3.5-6MHZ) with low power to reduce risk of
biological effects. use of Doppler should be avoided in the 1st
2 hours before the appointment time, empty your bladder. Over the
next hour, drink at least 1 liter of water and do not go to the toilet
Cervix - assess if closed and measure length between internal and
Look for bright trophoblastic reaction around sac.
Assess placental location and distance from internal os (may lie close to
os at this stage)
Check for retroplacental hemorrhages, placental masses etc
Assess maternal ovaries, adnexae and Pouch Of Douglas (P.O.D)
Confirm presence of intrauterine gestation, and number
If multiple pregnancy, confirm number of fetuses, number of sacs, and
number of placentas present to determine chorionicity. i.e.
(MCDA),Dichorionic /Diamnionic (DCDA)
Confirm heart beat(s) & rate with M-Mode only (Use of Colour or Doppler
traces is not recommended in the 1st trimester)
Measure CRL to calculate gestational age and Estimated Date of
If too early to see the fetal pole measure the average sac diameter.
A 1st trimester series should include the following
Uterus - long, trans
Cervix and Pouch-Of-Douglas
Gestational sac - Long & Trans
Yolk sac if visible
M mode fetal heart
Document the normal anatomy. Any pathology
found in 2 planes, including measurements.
The gestational sac(GS) is the earliest sonographic
finding in pregnancy. It will be difficult to see if the
mother has a retroverted uterus or fibroids. The GS is an
echogenic ring surrounding an anechoic centre. An
ectopic pregnancy will appear the same but it will not be
within the endometrial cavity. The GS is not identifiable
until approximately 4 1/2 weeks with a transvaginal
Gestational sac size should be determined by measuring
the mean of three diameters. These differences rarely
effect gestational age dating by more than a day or two.
The following image is using a transvaginal approach the
gestational sac can be seen during week 4-5.
5 week gestation. Yolk Sac Only seen.
The yolk sac will be visible before a
clearly definable embryonic pole.
Mean Sac Diameter measurement is used to
determine gestational age before a Crown Rump
length can be clearly measured. The average sac
diameter is determined by measuring the length,
width and height then dividing by 3
The very early embryonic heart will be a
subtle flicker. This may be measured using
M-Mode(avoid Doppler in the first
trimester due to risks of bioeffects).Initially
the heart rate may be slow.
The Crown Rump Length (CRL) measurement
in a 6 week gestation. A mass of fetal cells,
separate from the yolk sac, first becomes
apparent on transvaginal ultrasound just
after the 6th week of gestation. This mass of
cells is known as the fetal pole.
The yolk sac appears during the 5th week. It is the second structure to appear
after the GS. It should be round with an anechoic centre. It should not be
calcified, misshapen or >5mm from the inner to inner diameter. Yolk sacs
larger than 6 mm are usually indicative of an abnormal pregnancy. Failure to
identify (with transvaginal ultrasound) a yolk sac when the gestational sac
has grown to 12 mm is also usually indicative of a failed pregnancy.
Using a transvaginal approach the fetal heart beat can be seen flickering before
the fetal pole is even identified. It will be seen alongside the yolk sac. It may be
below 100 beats per minute but this will increase to between 120- 180 beats per
minute by 7 weeks. In the early scans at 5-6 weeks just visualizing a heart beating
is the important thing. Failure to identify fetal cardiac activity in a fetus whose
overall length is greater than 4 mm is an ominous sign.
Sometimes there is difficulty distinguishing between the maternal pulse and fetal
heart beat. Often technicians will take the mothers pulse at the same time to
check if it is the fetus or the mothers .
CROWN RUMP LENGTH (CRL)
The CRL is a reproducible and accurate method for measuring and dating a
Early ultrasonographers used this term (CRL) because early fetuses also
adopted the sitting in the chair posture in early pregnancy. After 12 weeks,
the accuracy of CRL in predicting gestational age diminishes and is replaced
by measurement of the fetal biparietal diameter.
In at least some respects, the term "crown rump length" is misleading:
There is no fetal crown and no fetal rump to measure for most of the first
Until 53 days from the LMP, the most caudad portion of the fetal cell mass is
the caudal neurospone, followed by the tail. Only after 53 days is the fetal
rump the most caudal portion of the fetus.
Until 60 days from the LMP, the most cephalad portion of the fetal cell mass is
initially the rostral neurospore, and later the cervical flexure. After 60 days,
the fetal head becomes the most cephalad portion of the fetal cell mass.
What is really measured during this early development of the fetus is the
longest fetal diameter.
From 6 weeks to 9 1/2 weeks gestational age, the fetal CRL grows at a rate of
about 1 mm per day.
Measure the crown rump length
(CRL) to estimate gestational age.
At 10 weeks, visualize 4 jointed
limbs, feet and hands.
From 12 weeks the basic
morphology of the fetus is visible
The Nuchal Translucency is used to provide
a risk assessment for chromosomal
abnormalities, specifically Trisomies 13,18
and 21 (Down's Syndrome).
The legs are usually crossed at the ankles. Confirm
the presence and symmetry of the long bones.
The correct angle the feet to legs can be
confirmed. They should be at 90 degrees i.e.
perpendicular or Talipes should be suspected.
The humerus, radius and ulna
and the presence of hands are
imaged from 11 weeks.
12 week choroids take up most
of the space within the ventricles.
Initially twins may be identified as 2 separate gestational sacs (i.e. diamniotic, dichorionic)
They may be 2 fetal poles within the same gestational sac (monochorionic). It is easier to
determine chorionicity earlier in the pregnancy depending on the chorionicity and
It is a sad situation when a "vanishing twin" occurs, which is about 20% of twin pregnancies.
In these cases, one of the twins fails to grow and thrive. Instead, its development arrests and
it is reabsorbed, with no evidence at delivery of the twin pregnancy.
Monoamniotic Twins. Dichorionic diamniotic Twins.
Triplets with 2 sacs. Monoamniotic, monochorionic twins and a normal single.
GRAPHS TO DETERMINE GESTATIONAL AGE
Depending on the age of the gestation, these graphs can be used to determine the correct EDD.
Mean Sac Diameter measurement is used to determine
gestational age before a Crown Rump length can be clearly
measured. The average sac diameter is determined by
measuring the length, width and height then dividing by 3.
Once a fetal Pole can be visualized the
CRL measurement is the most accurate
method for dating the pregnancy.
Thickened Nuchal Translucency (NT):
• One of the parameters used in sequential screening (SS) for Down’s syndrome in first trimester
– SS: Pregnancy associated plasma protein levels, hCG levels, NT thickness
• Measured during 11-14 wks gestational age
• Seen on sagittal image as increased subcutaneous non-septated fluid in posterior fetal neck
• Measurement >3mm usually considered abnormal, however exact cut off measurements are
dependent on maternal age/gestational age
• Detection rate of screening for Down’s Syndrome in first trimester:
– sequential screening with NT: 82-87%
– NT alone: 64-70%.
PARTIAL OVULAR DETACHMENT
The maternal circulation inside the placenta starts peripherally (in
the placental margins) and is associated to physiological oxidative
phenomena that may lead to membranes rupture and formation.
The abnormal development of such membranes may result in
subchorionic hemorrhage, enhancing the predisposition to an
adverse gestational outcome at the third trimester (PPROM and
Such abnormality is common and also denominated as subchorionic
hemorrhage or trophoblastic hematoma, being visualized in more
than 18% of cases of threatened miscarriage. The presence of fetal
heart activity confers an excellent prognosis. Clinically, subchorionic
hemorrhage may course with vaginal bleeding. At ultrasonography,
a crescent-shaped shadow is observed adjacent to the gestational
sac, with debris. Gestational sac compression and consequential
deformation may occur. In most of cases, a two-week follow-up
evaluation confirms the hematoma resorption.
Retained products of conception are characterized by a
thickened, disorganized and heterogeneous endometrium, with ill-
defined mucosal layers and cavitary line, either with or without the
presence of gestational sac. Clinically, the women presents
abdominal pain and relative vaginal bleeding(1,4). In the presence of
an intact gestational sac and closed cervix, the difficulty in a
spontaneous resolution will be higher, requiring surgical evacuation
EARLY EMBRYO DEATH
Some sonographic findings characterize an embryo death in the first half of the
first trimester in early phases, before the crown-rump length can be measured.
The following aspects are highlighted: small, hyperechoic yolk sac, or hydropic
yolk sac increased in volume with diameter > 7 mm, or even small amniotic cavity
disproportionate to the gestational sac size. Before the 9th week, small
gestational sac may be associated with aneuploidy.
At transvaginal ultrasonography, the yolk sac should be visualized in a gestational
sac with mean diameter > 10 mm. The absence of a yolk sac within the gestational
sac with > 10 mm in mean diameter, or the absence of a yolk sac within the
gestational sac with > 16 mm in diameter characterize anembryonic gestation
IMAGES FOR ANEMBRYONIC PREGNANCY (BLIGHTED OVUM PREGNANCY).
IMAGES FOR ANEMBRYONIC PREGNANCY (BLIGHTED OVUM PREGNANCY).
GESTATIONAL TROPHOBLASTIC DISEASE
The typical sonographic finding in most of cases of complete hydatidiform
mole is a echogenic, intracavitary solid mass with intermingled, small cystic
loci resembling a "snow storm", corresponding to the vesicles that
macroscopically characterize this condition.
The higher the gestational age, the larger the vesicles visualized as
homogeneous anechoic images, increasing the method specificity. The
ultrasonography sensitivity will depend on the gestational age at the moment
of the diagnosis. Ultrasonography can detect vesicles with > 2 mm in
diameter. In early pregnancies with trophoblastic disease, the sonographic
method accuracy is limited, hindering the differentiation of gestational
trophoblastic disease from other conditions involving the endometrial cavity.
Partial hydatidiform mole offers higher diagnostic difficulty by
ultrasonography. In a reasonable number of cases, this disease presents as
an empty gestational sac corresponding to anembryonic gestation, or as
early embryo death. However, two criteria have been described in the
literature: gestational sac transverse/anteroposterior diameter ratio > 1,5
and cystic changes, irregularity of increase in echogenicity of
decidual/placenta or myometrial reaction
Sonographic findings of ectopic pregnancy will vary as a
function of the gestational age and site.
Classically, the following sonographic findings are
described: tubal ring sign, adnexal disorganized mass
molded to the adnexa and/or cul de sac, solid, organized
mass with regular margins mimicking a pediculated
myomatous nodule, clinically progressing with low β-hCG
levels, and presence of a live extrauterine conceptus.
Uncommon gestational sites may be observed such as
abdominal ectopic pregnancy, cervical ectopic pregnancy
and ectopic pregnancy in a previous Cesarean section
Subchorionic hemorrhage (SCH) occurs when there is
perigestational haemorrhage and blood collects between the uterine
wall and the chorionic membrane in pregnancy. It is a frequent cause
of first and second trimester bleeding.
It typically occurs within the first 20 weeks of gestation. If seen in the
first 10-14 days of gestation, they are also sometimes termed
crescentic collection with elevation of the chorionic membrane
depending on the time elapsed since bleeding, the collection will have
acute: hyperechoic and may be difficult to differentiate from
subacute-chronic: decreasing echogenicity with time
in almost all cases there is extension of the hematoma towards the
margin of the placenta.
Conjoined twins are a rare and complex complication of
monozygotic twinning, which is associated with high perinatal mortality.
Early prenatal diagnosis of conjoined twins allows better counselling of
the parents regarding the management options, including continuation of
pregnancy with post-natal surgery, termination of pregnancy or selective
fetocide in case of a triplet pregnancy. With the introduction of high-
resolution and transvaginal ultrasound imaging, accurate prenatal
diagnosis of conjoined twins is possible early in pregnancy. Although first-
trimester diagnosis of conjoined twins is feasible, false-positive cases are
common before 10 weeks because, earlier in gestation, fetal movements
are limited and monoamniotic twins may appear conjoined. As most
parents opt for immediate termination of pregnancy at confirmation of
the diagnosis, there are limited data on the prenatal follow-up of
conjoined twins. detailed analysis of case reports where 3D imaging was
used indicates that this modality does not improve on the diagnosis made
by 2D ultrasound. Overall, very early prenatal diagnosis and first-trimester
3D imaging provide very little additional practical medical information
compared to the 11-14 weeks' ultrasound examination.
Images of the conjoined twins, there are two heads with conjoined body.
Conjoined twins. Ultrasound images of fetuses joined at the pelvis and chest, with separate heads.
Three-dimensional sonogram showing the conjoined
twins of the thoraco-omphalopagus type.
First Trimester: Bleeding/Miscarriage, Molar Changes.
Miscarriage is defined as the loss of a pregnancy prior to the completion of 24 weeks
gestation and the main maternal symptoms are bleeding and pain. If a fetal HR has
been detected, the risk of spontaneous miscarriage in singletons is 12.2%.
Threatened Pregnancy Failure.
First trimester obstetric abnormalities are identified by
screening studies or in cases of abnormal vaginal
bleeding with the objective of determining the
gestation viability. Transvaginal ultrasonography is the
method of choice in the evaluation of first trimester
pregnancy. In the presence of vaginal bleeding, this
method is highly specific in the determination of the
conceptus viability, most of times clearly defining the
etiological process involved in the clinical condition. The
knowledge of the sonographic findings that
characterize each condition is essential for determining
an appropriate clinical approach in these cases.