Predictive Value of Yolk Sac in Early Pregnancy by Ultra-Sonography

Predictive Value of Yolk Sac in Early Pregnancy by Ultra-Sonography

Presented by Dr. Narayan M. Patel
Prof. Emeritus, ob/gyn.muni.medical collage,
Postal address: - Mahalaxmi institute of medical teaching
3, shantiniketan park, Nr. S. P. Colony
Ahmedabad-380014 Gujarat state (INDIA)
Phone: - (079) 27682572
Email: narayanpatel1932@yahoo.com

Yolk sac
1979: Mantoni & Pederson, first visualized yolk sac with static ultrasound equipment
1980: Sauerbrel & Croozi adopted real time imaging

Primary yolk sac is a microscopic structure and not seen on ultra sound.

What we see on ultra sound is the secondary yolk sac. Yolk sac is a spherical membrane quite ecogenic and readily seen at sonography.

Early embryo develops along the outer margin yolk sac as shown by arrow.

The yolk sac is attached to the embryo by the body stalk and flouts freely in the extraemryonal coelom, until 10th week.

By seventh week the yolk sac occupies a space between the chorion and fetus. At this gestational age, it has an important prognostic role. At 10th week with increasing growth of embryo, yolk sac become smaller and smaller and displaced at periphery. After 12-14 weeks yolk sac is no longer seen.

Yolk sac and gestational sac
1) Y.S. may be visible earliest, when mean sac diameter of G.S. is 8 mm.
2) one must see yolk sac when G.S. is 13 mm. or more
3) Y.S. if not seen, when G.S. is more than 20 mm. it means it is a case of blighted ovum.
4) The yolk is a definitive evidence of a true gestational sac.
5) Presence of yolk sac confirms intrauterine pregnancy
6) Presences of yolk sac however does not guarantee a normal out come of pregnancy.

Size of Yolk sac

YOLK SAC

Yolk sac is the first structure to be seen at T.V.S. even before fetal pole is seen. This patient had L.M.P. 1 month 7 days and yolk sac is seen.

Foetal pole and yolk sac may not be seen in the same plane at sonography, as shown in this slide

In measuring yolk sac inner to inner diameter is to be measured.
The walls of yolk sac are not to be included in the measurement.
Yolk sac diameter refers to mean inner diameter of yolk sac.

A yolk sac diameter more than 5.5 mm between 5 to 10 weeks of menstrual age, is associated with poor outcome.
A gestational sac with a mean diameter of more than 8 mm without a yolk sac, indicate non-viability.

The exact functions of the yolk sac are largely unknown.
It may play a role in:-
(1) Transfer of nutrients to the embryo. It has been shown that the yolk sac is the source of several embryonic proteins, including alpha fetoprotein, transferin, pre albumin, albumin. alpha antitripsin and apolipo proteins.
(2) Haematopoiesis
(3) Formation of primitive gut.
(4) Germ cell formation.

An enlarged yolk sac, greater than 6 mm in diameter can be the first sign of an eventful pregnancy failure.
Yolk sac that is
Too small,
Solid,
Too large
Fragmented, or
Irregular,
is associated with poor pregnancy outcome.

Yolk sac at L.M.P. 2 months
Yolk sac 6.2 mm. A poor prognosis was forcasted to the patient.

Big yolk sac measuring 6.5mm
Big yolk sac measuring 6.2mm

Both cases has poor prognosis.

Large yolk and Fractured yolk sac

Poor prognosis in both the cases

Big yolk sac and no fetal pole. A case of blighted ovum.

Gestational sac is irregular. Measures 18mm. No fetal pole or yolk sac seen. Confirms as missed abortion.

L.M.P. 2 months. Big yolk sac of 6 mm in diameter. No fetal pole. A case of blighted ovum

Large yolk sac of 6.8 mm. Fetal pole is seen. However prognosis in this case will be poor.

Abnormally large yolk sac results from accumulation of nutrients, not used by the embryo.

1-This Pt., Mrs. M, had yolk sac of 6.5 mm in early pregnancy. She was told that prognosis likely to be not good.
2-On further follow up, Mrs. M, at 10 weeks pregnancy the Yolk sac decreased in size and there is no fetal pole even at 2 months 8 days preg. Confirmed as blighted ovum.

Small and irregular yolk sac at early pregnancy.

However in this case Yolk sac become regular and of normal size on follow up. So if in doubt, full cases follow up is mandatory.

Yolk sac

A case of Bin ovular twins. Yolk sacs are seen in both gestational sacs. Fetal poles are not seen in this view. In multiple pregnancy embryonic well beings can and should be documented at every visit, until the pregnancy is past first trimester.

A case of twins pregnancy. L.M.P. 1 month 25 days
Both fetal poles are well seen. Yolk sacs not seen in this view

Yolk sac

A case of Triplets. Three sacs are seen, marked as 1, 2 and 3
Yolk sacs are seen faintly in No 1 and No 3, as shown by arrow

Yolk sac and Rhobencephalon (not to be mistaken As second Yolk sac)

L.M.P. 1 month 25 days. Yolk sac is seen shown by arrow
In the fetal pole in head, shows a collection of fluid-called Rhombencephalon. It mimics a second yolk sac. Be careful not to describe it as second yolk sac.

If only one ultra sound is to be performed in a pregnancy, then the 8 week ultrasound provide the most reliable information of eventual out come of pregnancy.

Embryonic period is between 5 to 10 weeks of menstrual age. This period is the most critical phase of prenatal development & most major anomalies are arising in this period.

Absence of yolk sac in presence of an embryo is always abnormal, and may follow embryonic demmise.
The anatomical and functional details obtained with Trans-vaginal ultrasonography in early pregnancy are very valuable for the care of pregnant woman.

Conclusion

Yolk sac of normal size, number & quality is a forerunner of normal pregnancy.
Monitoring of yolk sac has got a definite predictive value in the well being of developing fetus.

Conclusion (Cont.)
• Recurrent abnormal yolk sac with early abortion is often due to chromosomal abnormalities.
•Regular USG monitoring of yolk sac is always desirable in early pregnancy.