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Sonography in the First Trimester

G. William Shepherd PhD, RDMS, RVT

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Basic Embryology

1mm

Sac

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Embryonic Timeline

Ovulation: Day 14-16

Fertilization: Day 14-16

Zygote to Morula: Day 16-18

Morula to Blastocyst: Day 18-19

Implantation: Day 19-20

Week 3

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Embryology Terms

Gamete --------- Before fertilization

Zygote ---------- After fertilization

Morula --------- 16 -32 Cells (18 Days)

Blastocyst ---------- 20 Days

Embryonic Disc --- 28 Days

Ultrasound Detection --- 31 Days

Earliest Heart Beat ------ 36 Days

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Yolk Sac Formation: 4w1d

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Goals for a 1st Trimester Scan

Visualization and localization of the

gestational sac

Determination of viability

Determination of the # of embryos & viability

Estimation of gestational age

Determination of any detectable anomalies

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4W6D

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Earliest Definite Ultrasound Visualization: 31days

Pre-embryonic (embryonic disc stage 4w4d or 32days)

coronal

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“Double Sac” Sign

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“Double Sac” Sign

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Age in Days (by LMP) = (L+W+H)

3 + 30

Estimation of Gestational Age

from the MSD (mean sac diameter)

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5 weeks by LMP

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5w0d by LMP

6mm

4mm

Width (from trv image) = 6

6+6+4 divided by 3 = 5.3, +30 = 35.3d or 5w

1cm

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x x

+

+

xx 13mm

++ 11mm

Width 15mm MSD 13 = 43d =6w1d

5 weeks 6 days by LMP

9.25

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Human Chorionic Gonadotropin

Made by trophoblastic cells

Detectable after implantation

Doubling time every 2-3 days

Correlates well with embryonic and sac size

Level maximizes at about 8 weeks

Max level is about 50,000 -100,000 IU/L

Declines after 10-12 weeks

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Beta Chorionic Gonadotropin Levels

MSD Age (weeks) HCG Level

2mm 5.0 1,164

5mm 5.4 1,932

10mm 6.0 4,478

15mm 6.6 10,379

20mm 7.3 24,060 * Filly, in Ultrasonography in Obstetrics and Gynecology, ed Callen, W.B. Saunders, Philadelphia, 1994.

CRL

4

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x x

4-5mm

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Embryonic Timeline

Week 6: Heartbeat will be detectable during this week.

This is the neural tube stage

Weeks 6-10: Essentially all of the tissues and organs

of the embryo will form during this period.

Week 11: All of the organs are present and all but a

portion of the bowel and the external genitalia are in

their final positions.

Week 12: The bowel will reenter the fetal abdomen.

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5w5d 6w1d

3 days development and growth 22

CRL and Gestational Age

CRL Gest. Age CRL Gest. Age

2mm 5.7 weeks 60mm 12.5 weeks

4 6.1 70 13.2

8 6.7 80 14.0

10 7.2 90 14.9

15 7.9 100 15.9

20 8.6 110 16.9

25 9.2 130 17.9

30 9.9

40 10.9 Hadlock et al

50 11.7 Radiology 18: 501, 1992

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Yolk sac and the Early Embryo

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6w3d

2mm

5

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Embryonic Period 8w

Fluid?

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CRL = 18mm 8w3d

Fluid?

Oblique Scanning Plane

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13mm

7w2d

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Don’t include the yolk sac in the CRL

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Be aware of fetal position

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31 32

6w1d 7w4d

8w4d 10w3d

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After 13 weeks use BPD, HC, AC, and FL

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Manipulation of Transducer for CRL

Video Clip

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8w2d 9w3d

Skeletal Development

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10w3d

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Indications for a First Trimester Scan

Vaginal bleeding

Size and date discrepancy

No heart tones

Pelvic pain

Accurate dating for future C-section

History of an anomaly

Trauma

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Significance of the Yolk Sac

Earliest landmark in the early gestational sac

Identifies an IUP

Helps to locate the embryo and heart beat

Should be round and “cystic” 3-6mm

1 yolk sac per embryo, can help identify

monoamnionic twins

Should disappear by 12 weeks

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7 Week Embryo

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7 Week Embryo

Amnion

Yolk Sac

Amniotic Fluid Chorionic Fluid

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Yolk Sac

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Yolk Sac

Too big

1 cm

1.5 cm

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Compressed Yolk Sac

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Vaginal Bleeding (1st Trimester)

Implantation Bleed

Abortion

Subchorionic Hemorrhage

Placental Previa

Ectopic Pregnancy

Blighted Ovum

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Implantation Bleed

Most common cause of 1st trimester

vaginal bleeding

Generally not significant

Sonolucent area between the chorion

and uterus (near the internal os)

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The future Jen Shepherd

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Vaginal Bleeding (1st Trimester)

Implantation Bleed

Subchorionic Hemorrhage

Abortion

Placental Previa

Ectopic Pregnancy

Blighted Ovum

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Subchorionic Bleeds

Can be behind the placenta

Can be behind the chorion lavae

Can be behind the chorionic plate of the placenta

Prognosis depends upon the cause and how much

of the placenta is involved: >1/3 prognosis worsens

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49 50

1/4 of placenta is separated from uterus

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8w2d

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Vaginal Bleeding: 1st Trimester Implantation Bleed

Subchorionic Hemorrhage

Blighted Ovum

Placental Previa

Ectopic Pregnancy

Abortion

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Blighted Ovum: Arrested or absent development of

the embryonic pole (trophoblasts develop)

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No embryo

or Yolk Sac

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Growth will fall off

HCG will level off

Sac may move

toward Cx

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Trophoblastic ring

may become irregular

and thin < 2mm

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Video Clip

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Vaginal Bleeding: 1st Trimester

Implantation Bleed

Abortion

Subchorionic Hemorrhage

Placental Previa

Ectopic Pregnancy

Blighted Ovum

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Placenta Previa

12w2d

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Vaginal Bleeding: 1st Trimester

Implantation Bleed

Abortion

Subchorionic Hemorrhage

Placental Previa

Ectopic Pregnancy

Blighted Ovum

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Glossary of 1st Trimester Terms

Abortion: Premature expulsion of the gestation

from the uterus

Incomplete Abortion: The expulsion of only a

portion of the gestational products from the uterus

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Inevitable Abortion

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Retained Products of Conception

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Findings for Embryonic Demise

Old Criteria

The Findings Below Depend upon Body Habitus

and Type of Transducer, Endovag or transabd

No Sac Growth on Serial Exams

No Cardiac Pulsations in a 5mm Embryo

No Embryo Seen in a Sac 25mm MSD

No Yolk Sac Seen in a 20mm MSD Sac

Trophoblastic Ring is not Intact

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Findings for Embryonic Demise

No Sac Growth on Serial Exams

A 7 -10 day interval between scans is

recommended

Give the embryo a chance

EV scanning is always best

Abdallah et al US Obstet & Gynecol 2011

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The Gestational Sac Grows about 1mm/Day

1 Week Should Give a Statistically Significant Increase in MSD

MSD = 3mm MSD = 10mm

Jan 4 Jan 11

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Findings for Embryonic Demise Slow Cardiac Pulsations in a 5 (now 7) mm Embryo in an

endovaginal ultrasound examination

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Reading an M-Mode

1 second

Heart rate only 60 bpm Heart rate 160 bpm

1 second

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Findings for Embryonic Demise No Cardiac Pulsations in a 9mm Embryo in a

transabdominal ultrasound examination

M-Mode No Heart-beat

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Video Clips

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Video Clips

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Video Clips

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Findings for Embryonic Demise No Embryo Seen in a Sac 18 (now 25) mm MSD in an

endovaginal ultrasound examination

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Findings for Embryonic Demise

No Embryo Seen in a Sac 25mm MSD in an

transabdominal or EV ultrasound examination

Was 20mm

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Findings for Embryonic Demise No Yolk Sac Seen in a 10mm MSD Gestational Sac

with endovaginal scanning

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Findings for Embryonic Demise No Yolk Sac Seen in a 20mm

MSD Gestational Sac with

transabdominal scanning

MSD 25mm

10.0 82

New Criteria for Embryonic Demise

No Sac Growth on Serial Exams

No Cardiac Pulsations in a 7 mm Embryo*

No Cardiac Pulsations in a 9mm Embryo **

No Embryo Seen in a Sac 25 mm MSD*

No Embryo Seen in a Sac 25mm MSD**

No Yolk Sac Seen in a 10mm MSD Sac *

No Yolk Sac Seen in a 20mm MSD Sac**

* endovaginal scanning

** transabdominal scan

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Small for Dates

Normal Pregnancy / Wrong Dates

Anembryonic Pregnancy (blighted ovum)

Ectopic Pregnancy

Fetal Demise

Oligohydramnios

Intrauterine Growth Retardation (IUGR)

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Anembryonic Pregnancy

Embryonic Demise

S < D

Oligohydramnios

Ectopic Pregnancy

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Ectopic Pregnancy 95% occur in the tube

5% are interstitial and

are the most dangerous

Cornual and cervical

ectopics are increasing

In vitro procedures

increase the chance of

ectopic pregnancy

Heterotopic: IUP plus

an ectopic

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Transabdominal scans

Endovaginal scans

Pseudo-sac

Pseudo-sac

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Ruptured Ectopic

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Cervical Ectopic Pregnancy

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Ectopic Pregnancy in Right Cornu

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Ectopic?

Uterus?

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Right & Left Horns of

Bicornuate Uterus

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Hemorrhagic Corpus Luteum Can Look Like an Ectopic

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Molar Pregnancy

Large for Dates

Vaginal Bleeding

Very High HCG

May be a live embryo

1 in 1200 pregnancies in the USA

Risk is 20-40 fold higher if patient had a previous molar pregnancy (1 in 30-60)

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There may or may not be a sac.

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Theca Lutein Cysts

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The arrow heads point to the major portion of the mole.

The white arrows point to echogenic invasive villi that extent

almost to the serosal surface of the uterus (black arrows).

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Partial Mole at 12 weeks -Top, 14 weeks - Bottom

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Video Clip

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Large for Dates

Normal Pregnancy / Wrong Dates

Molar Pregnancy

Gestation with Mass / Masses

Multiple Gestation

10.25

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Bicornuate Uterus

IUP

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Hydatidiform Mole Theca Lutien Cysts

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Early Pregnancy with a Mass

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Multiple Gestation

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Video Clip

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Bleeds

Triplets

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1

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A

B

C D

E

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Anomalies: Detectable in the 1st Trimester (Endovaginal Scanning is Best)

Anencephaly

Acrania

Cystic hygroma

Hydrops

Conjoined twins

Large omphalocele

Severe gastroschisis

Thanatophoric dwarf

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Normal Head at 12 Weeks

Transverse Head at 12 Weeks

Choriod Plexus

Frontal

Occipital

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Video Clip

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Acrania at 10w2d

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Normal Nuchal Translucency 10w6d

2mm

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Normal Herniation of the Gut

into the Base of the Cord at 11w2d

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Omphalocele

12w4d

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Questions?