Normal First Trimester

Normal First Trimester

Fetal Biometry WorkshopDay 1

Objectives

Describe maternal & fetal early OBPlacenta & Fetal MembranesNormal Sonographic Anatomy & Landmarks1st Trimester Assessment & dating

Terminology

Conceptual ageGestational age / Menstrual age TrimesterEmbryonic phase

Trimesters

1st Trimester is 0-12 weeks2nd Trimester is 13-28weeks3rd Trimester is 28 - 40 weeksPost dates = after due date

Indications 1st TrimesterTo confirm presence of intrauterine pregnancyTo evaluate a suspected ectopic pregnancyTo define cause of vaginal bleedingTo evaluate pelvic painTo estimate gestational [menstrual] ageTo diagnose or evaluate multiple pregnancyTo confirm cardiac activityAs an adjunct to chorionic villus sampling, amniocentesis, embryo transfer, IUCD removalTo evaluate maternal pelvic masses and/or uterine abnormalitiesTo evaluate suspected hydatidiform mole

Patient History TakingPatient ageLMP – normal or notSymptomsPelvic ProceduresReproductive History

GravidityParityG3P1012

Lab Tests

UrineDetects HCG in urine

positive or negative

Urinalysis throughout the pregnancy

BloodMSAFP

Alpha feto protein, serum blood Maternal blood & amniotic fluidProduced by yolk sac, then fetal liverDone 15-22 wks

hCGHuman chorionic gonadotropinPlacental trophoblast cells Blood test most accurate

Early Development

Implantation Sites

Normal Upper corpusFundal region

EctopicFallopian tubes [97%]Uterine cornua [2.5%]]Non-tubal sites

OvariesCervixAbdomen

Early Intrauterine GestationDecidual Reaction Cast

Non-specific finding 3-4 weeksFocal echogenic thickening of deciduaThick endometrium tissue

Early Intrauterine Gestation

Decidual CystNot always visualized2 to 5 mm fluid collectionNo echogenic border Association with or before normal intrauterine gestation

Early Intrauterine Gestation

Implantation BleedMay follow implantation due to erosion of uterine liningHypoechoic cleft in decidua near sac

Intradecidual sign

Gestational sac within the decidua abutting the endometrial canalShould always be seen when maternal serum -hCG is 1700-2000 mIU/mL

Double Decidual Sign

Double-decidual sign

DDS [double decidual sign]

2 concentric hyperechoic rings adjacent to gestational sac

Inner decidua capsularis / smooth chorion

Outer decidua parietalis / developing placenta

Sonolucent center fluid-filled chorionic

cavity

Gestational Sac1st reliable indicator of IUP2 separate fluid filled compartments

Amniotic & chorionicYolk sac & embryoImplants in uterine fundusRounded in shape

MSD + hCG5 mm MSD = hCG of 1800 mU/mlContinue to increase proportionally

MSD

Vitteline DuctYolk stalk, omphalomesenteric ductProvide blood flow to YSFuses at 7-8 weeks Arteries then provide blood flow for foregut, midgut, and hindgut.Vitteline vein drain into the sinus venosus

3 paired vitteline veins

Yolk sac sign

Visualization of the yolk sac within the gestational sacYolk sac often seen when MSD is 5-6 mm and always seen when MSD is 8mm

Yolk SacWithin chorionic sacMSD

10 mm TV20 mm TA42 days or 6 menstrual weeks

MSD & Yolk Sac

Early Intrauterine Gestation

Embryonic Pole1st appearance of fetus~ 45 menstrual daysStraight

echogenic line

Gestational AgeGestational Sac Size

MSD = Length + Width + Height / 3

Yolk Sac SizeSeen in MSD of 10 to 15 mm

Crown-rump lengthEmbryo @ longest length

Predicting Viability

Cardiac activityHeart rate

Bradycardia – 1st trimester demiseLower limits of normal 100 bpm [<6.2 wks]Lower limit of normal 120 bpm [6.3 -7 wks]

Gestational Sac sizeSmall – poor outcome

MSD - CRL mm > 5 mm; if < poor outcomeYolk Sac

Size [large or small] & shape

Cardiac Activity

Embryo at 7 to 9 WeeksEarly umbilical cord

Connecting stalk attaches embryo to developing placenta [chorion frondosum]

Early development of limbs, midgut & CNSLarge rhombencephalic cavity in head

Embryo at 9 to 12 WeeksDeveloping anatomy visualizedExtremities develop>11 weeks bowel returns to abdominal cavity Fetal calvarium well formed [12 weeks]Lateral ventricles contain prominent choroid

Placenta & Membranes

Placental Development

1st Trimester - Placental Growth

Forms from chorionic villi Visible at 7 to 8 weeks’

Structural AbnormalitiesEarliest time abnormality can be detectedEarliest time abnormality should be detected1st trimester:

OmphaloceleDuodenal atresiaOcular defectsCardiac defectsSeptated cystic hygromasBifid appearance – conjoined twins

Growth Evaluation by US

Measurements

GSCRLBPDOFDHCACHC/ACFemur (humerus, ulna, tibia can be done as well but not routine)FL/BPDFL/ACFetal weight estimates (need BPD, AC, and FL)

Guidelines for Dating 1st Pregnancy

5.0 weeks gestational Age Gestational sacNo YS, embryo, or HB

5.5 weeks GA Gestational sac and YSNo embryo, or HB

6.0 weeks GA Gestational sac, YS, very small fetal pole that may be difficult to measure

Gestational Sac

100% specific for no PregnancyMSD grows about 1mm/day up to 10 weeks gestationMeasure inner to innerIf GS > 25mm and No embryoIf GS > 20mm and No YS(L x W x H) / 3 = mean sac diameter (MSD)GA (days) = MSD (mm) +30(TA) MSD of 5mm should = 5 wks GA(TV) MSD of 2-3mm = 4 wks GACan not definitively age a pregnancy on MSD alone

Gestational Sac

CRL measurement

BPD - Biparietal diameter

BPD - Biparietal diameter

OFD – Occipitofrontal Diameter

HC - Head circumference

Same view as BPDLength of outer perimeter of skullUse ellipse or trace

(D1 x D2) x 1.57

Cephalic Index

CI = (shortest axis, BPD/ longest axis, FOD) x 100= 78.3Measure outer to outerNormal mean = 78.3Dolicocephalic <70Brachycephalic >86

BPD and Abdominal Diameter Comparisons

Up to 13 wks head >Abd13-33 wks Head = Abd>33 wks Head < Abd

Femur Length

Measure longest axis of femoral shaftWhere angle of Greater Trochanter is seen>12 weeks can be measured14-22 wks + 1 wk, most accurate timeGrowth rate: 2-3 mm/ wkRemember no bent femurs

FL –Femur Length

AC - Abdominal Circumference

Review – Sequential appearanceMenstrual Week Structure

4 -5 Gestational sac

5 Yolk sac

5.5 – 6 Fetal heart beat

6 Fetal pole

7 Single ventricle

7.5 Spine

7.5 Lower limbs

8 Upper limbs

9 Falx

9 Body movements

9.2 Limb movements

9.5 Midgut herniation

9.5 Choroid plexus

9.5 Hindbrain

12 Fingers

12 Jaw

12.5 Toes

1st Trimester Imaging

Visualization and localization of the gestational sac (intrauterine or ectopic pregnancy)Identification of embryonic demise or living embryonic gestationIdentification of embryos that are still alive but at increased risk for embryonic or fetal demiseDetermination of the number of embryos and the chorionicity and amnionicity in multifetal pregnanciesEstimation of the duration or menstrual age of the pregnancyEarly diagnosis of fetal anomalies, including identification of embryos that are more likely to be abnormal based on secondary criteria (abnormal yolk sac)