Predictive Value ofYolk Sac

in Early Pregnancyby Ultra-Sonography

Presented by

Dr. Narayan M.PatelM.D,D.G.O.,F.I.C.S

Prof.Emeritus, ob/gyn.muni.medical collage,Postal address:-Mahalaxmi institute of medical teaching3, shantiniketan park, Nr. S. P. ColonyAhmedabad-380014 Gujarat state (INDIA)Phone:- (079) 27682572E-mail:-narayanpatel1932@yahoo.com

1979: - Mantoni & Pederson, first visualized yolk sac with static ultrasound equipment1980:- Sauerbrel & Croozi adopted

real time imaging

Yolk sac

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

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

Secondary yolk sac

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

Fetal pole

Yolk sac

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

Foetal pole

Amnion

Yolk sac

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 displacedat periphery. After 12-14 weeks yolk sac is no longer seen.

Yolk sac and gestational sac1) 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 more3) 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

pregnancy6)Presence of yolk sac however does not

guarantee a normal out come of pregnancy.

.

Size of Yolk sacWeeks of gestation Yolk sac diameter

5 weeks 3 to 6 mm6 weeks 4 to 5 mm7 weeks 5 mm. (Embryo seen)8 weeks 5 mm. (embryo 10mm)

After 7 weeks yolk sac is static, till it disappear by the end of first trimester. Normal acceptable size of yolk sac 5.0 .to 5.5mm

Yolk Sac Seen at G.S. diameter.

By T.V.S. 5 weeks preg. 8 to 10 m.m.

By T.A.S. 6 weeks preg. 20 mm

At transvaginal sonography, yolk sac is seenone week earlier than trans abdominal sonography.

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

Fetal pole

Yolk sac

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 isToo small,Solid, Too large Fragmented, or Irregular,is associated with poor pregnancy out come.

Fotal pole

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

Both cases has poor prognosis.

Big yolk sac measuring 6.5mm l

l

Big yolk sac measuring 6.2mm

Poor prognosis in both the cases

Large yolk Fractured yolk sac

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

Measures 18mm.No fetal pole or yolk sac seenConfirms as missed abortion

L.M.P. 2 months. Big yolk sacof 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 pregnancythe Yolk sac decreased in size and there is no fetal poleeven at 2 months 8 days preg. Confirmed as blighted ovum.

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

Small and irregular yolk sac at early pregnancy.

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

Yolk sac

Yolk sac

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

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

Yolk sac

Yolk sac

L.M.P. 1 month 25 days. Yolk sac is seen shown by arrowIn the fetal pole in head, shows a collection of fluid -called Rhombencephalon. It mimics a second yolk sac. Be carefulnot to describe it as second yolk sac.

Yolk sac

Rhobencephalon(not to be mistakenAs 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 demise.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.