U/S Stages of Pregnancy

• Thickened endometrial stripe
• Double-decidual sign
• Gestational Sac
  
• Yolk sac
• Fetal pole
  

Double Decidual Sign

• Two rings made up of decidua parietalis (uterine cavity lining) and decidua capsularis (gestational sac lining)
• Rings surround anechoic gestational sac
• Interface of two rings is the decidua basalis (where the placenta will form)
• 5-6 weeks
  
• Cannot rule out ectopic with this u/s finding
  

Gestational Sac

• Cavity of fluid around the embryo
• Anechoic space with white rim
• 4-6 weeks
  
• Cannot rule out ectopic with this u/s finding
• Grows by about 1 mm per day up to 9 weeks
  

Yolk Sac

• First accepted U/S proof of IUP
• Should be inside the Gestational Sac
  
• Looks like a cheerio
• 5-6 weeks
  

Fetal Pole - Crown-Rump Length (CRL)

• Do not include yolk sac in the measurement
• Accurate w/in 5-7 days

Fetal Pole - Biparietal diameter

• Can predict gestational age within ±7 days when measured between 14 and 20 weeks of gestation
• Accuracy diminishes as the gestation progresses beyond this period
• BPD is measured on a plane of section that intersects both the third ventricle and thalami

Ectopic Pregnancy

• 1-2% of all pregnancies
• 95-97% are in the fallopian tube
• Can also embed in ovary, cervix, abdomen, or interstitial
• Only 20% of ectopics definitively diagnosed on u/s
• An ultrasound can rule-in but NOT rule-out an ectopic
  

Gestational Trophoblastic Disease

• Hydatidiform mole (most common), partial mole, trophoblastic tumor, choriocarcinoma
• Elevated hcg, uterus large for gestational age, VB
• "Cluster of grapes"

Heterotopic Pregnancy

• Rare unless in the setting of IVF