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OB: 1st Trimester

!! hCG doubles every 2 days in normal pregnancy

Mean Gestational Sac Diameter (MGSD)

Anechoic space is measured in 3 dimensions and averaged. The sac grows 1.2 mm/d.

Sonographic detection

  • Gestational sac (chorionic sac) identified at 5 weeks. hCG > ~ 1500 IU/L. Cannot differentiate from pseudogestational sac.

  • Gestational Sac + Yolk Sac at 5.5 weeks. Should see YS at MGSD of 8 mm. Presence of YS rules out pseudogestational sac of ectopic pregnancy. hCG ~ 7000 IU/L

  • GS + YS + Embryo (within amniotic sac [double-bleb sign]) is seen at 6 weeks. Should see Embryo at MGSD of 16 mm (new 25 mm), hCG ~ 11.000 IU/L. Heart Beats HB (cardiac activity) at > 5 mm CRL --> proof of living IUP. Embryo measuring 7 mm w/o HB ==> Failed pregnancy. 6.5 weeks pregnancy w/o HB ==> Failed pregnancy.

Intradecidual sign

GS is an anechoic space surrounded by hyperechoic rim of trophoblastic tissue and thickened decidua.

1st trimester oligohydramnios

If MGSD-CRL < 5mm → 95% abort spontaneously

Double decidual sac sign

As the GS grows, it will obliterate hypoechoic endometrial canal so there will be 3 layers
it confirms normal IUP. Not seen w/ pseudogestational sac or abortion.

Subchorionic bleed

Implantation hematoma is a collection of blood in the endometrial canal between chorion and decidua. If subchorionic bleed > 50% of GS --> poor prognosis.

Heart Beat limits


Impending, In progress, Incomplete, Missed

Hydatidiform Mole

+ preg.test and multiple hypoechoic and hyperechoic spaces filling and distending the endometrial canal w/o well defined embryo - may mimic spontaneous incomplete abortion

Clinical Triad: enlarged uterus, hyperemesis, hCG>100.000

malignant potential for choriocarcinoma; 50% will have bilateral multiseptated cystic ovarian masses - theca lutein cysts suggest gestational trophoblastic disease

DDx: partial mole with hydropic placental changes