Sonological mile stones in very early normal pregnacies

When the Honorable guest (embryo) will be imagable in the TVS screen?? Trailer of the film?? Ans:- Let me go back before the image of embryo(embryonic  pole) is imagable. But we have to remember that pritrophoblastic color flow at the focal decidual thickening precedes the visibility of embryonic pole. Now let us quickly review what we have to remember in  very early scan?? Ans:- Event 1:-The blastocyst implants into the endometrium by approximately 23 days of menstrual age It measures 0.1 mm but at that time it is  too small to be visualized on TVS. So, on cycle Day 23 :-- Blastocyst implantation :-Blastocyst measures 0.1 mm and is too small to visualize

3.5– 4 wk Event 2 :-Demonstration of peritrophoblastic flow by transvaginal color flow Doppler at this focal decidual thickening has improved the diagnostic sensitivity of intrauterine pregnancy (IUP) from 90% with TVS alone to 99% using transvaginal color flow Doppler .The peritrophoblastic flow has a characteristic high-velocity and low-impedance flow caused by shunting of blood from the spiral arteries into the intervillous spaces. The  peak systolic velocity of peritrophoblastic flow in a normal IUP ranges from 8 to 30 cm/second, before the visualization of the gestational sac. Decidual changes at implantation site in the form of

focal echogenic decidual thickening at implantation site

4– 4.5 wk due to trophoblastic tissue high-velocity and low-impedance trophoblastic flow at the implantation site

on TVs- CFD

Land marks of normal first-trimester pregnancy

Gestational age Embryologic change Sonographic appearance 4.5– 5 wk Exocoelomic cavity of the blastocyst

Event  3 Gestational sac (a sonographic term) is always seen when it measures > 5 mm and the serum b-hCG is between 1000 and 2000 mIU/mL (IRP) In normal pregnancy serum b-hCG should double or increase by at

least 66% in 48 hours.

. Event  3A  At 5– 5.5 wk Secondary yolk sac  will be visible. Yolk sac is seen as a thin-walled cystic structure within the gestational sac andshould always be seen when the GS is > 10 mm; it is the first sign of a true gestational sac before the visualization of embryo 5– 6 wk Yolk sac

The first structure to be seen within the gestational

sac is the secondary yolk sac, which is a reliable

indicator of a true IUP with a positive predictive

value of 100%. The primary yolk sac is not seen by

US because it shrinks at 4 weeks menstrual age and

gradually disappears with the formation of the secondary

yolk sac . The secondary yolk sac is first

seen on TVUS as a thin-walled cystic structure by the

fifth gestational week and is virtually always seen by

5.5 weeks gestational age. The yolk sac

is round, measures less than 6 mm, and should be

visualized by TVUS when a gestational sac measures

more than 10 mm  . The yolk sac is involved in

nutritive, metabolic, hemopoietic, and secretive functions

during early embryonic development and organogenesis

. Abnormalities in its size and appearance are predictors of abnormal gestation

Apperance of events in TVS in nrmal very early pregnancies:-Event No   4  embryonic disk is initially seen as a focal echogenic area of 1- to 2-mm thickness adjacent to the

yolk sac between 5 and 6 weeks of gestational age

Embryo Seen as a focal echogenic area adjacent to the yolk sac; should always be seen  when the GS is > 18 mm 5– 6 wk The embryo should always be visualized by

TVS when the gestational sac measures greater than

18 mm, and transabdominally when the gestational

sac measures 2.5 cm . With the currently

available high-frequency transvaginal transducers,

the embryonic disk is initially seen as a focal echogenic

area of 1- to 2-mm thickness adjacent to the

yolk sac between 5 and 6 weeks of gestational age

 Event  5   Embryonic cardiac activity Event  6 :-  Embryonic cardiac activity should always be seen when the embryo is > 5 mm; What is hear rate at so early stage?? Ans:-normal heart rate ranges from 100– 115 beats/min between 5 – 6 wk of gestation with hyperechoic margins (arrow) and endometrial cavity Embryonic cardiac activity should always

be seen when an embryo measures greater than 5 mm.

Occasionally the hear  tbeat may be seen adjacent to

the yolk sac even before the embryo is clearly visible.

Although visualization of a living embryo does not ensure a viable pregnancy, the abortion rate decreases for living embryos as the gestational age increases, with a 0.5%

demise rate for living embryos between 6 and 10 mm

.If the length of the embryo is less than 5 mm,

follow-up US should be performed until the expected

CRL exceeds the discriminatory value. Most of the

studies reported a heart rate of 100 to 115 beats per

minute between 5 and 6 .By 9 weeks

of gestational age, the mean heart rate increases to

about 140 beats per minute. The cardiac activity

should be documented by M-mode.

Amniotic sac

The amniotic sac is formed in the fourth week

of gestation between the ectoderm layer and the adjacent

trophoblast. Before 6.5 weeks the amniotic

membrane is so close to the embryo that the amniotic

cavity around the embryo is not easily seen. The diameter of the amniotic cavity is nearly equal to the CRL. Between 5 and 7 weeks of gestational age the embryo is located between the amniotic and yolk

sacs. On US, this amniotic sac–embryo–yolk sac complex appears as two small sacs and is called the double bleb sign The embryo and the inner

amnion grow at a faster rate than the outer chorionic

cavity with eventual fusion of the amniotic and

chorionic membranes by 16 weeks of gestation