OB quiz 3

Evidence of an intrauterine pregnancy in the form of a gestational sac should be sonographically visualized transabdominally when the serum HCG level reaches *** 1800 MIU/ml [milli International Unit] (Second International Standard {2nd IS}), or 3600 MIU/ml (International Reference Preparation {IRP}) also called First International Reference Preparation - same value as Third International Reference Preparation.

With transvaginal scanning, the discriminatory zone is about 800 to **1000 mIU (2nd IS) or 1000 to **2000 (IRP), when a 2 to 3 mm gestational sac can be seen in the midst of dense decidua.

Double bleb

amniotic sac and the yolk sac

Double dicidua

brightness that surrounds a sac its so new u dont see shit in it

The average human pregnancy is 40 weeks in length or 280 days, beginning with the first day of the last menstrual period (LMP). Menstrual age refers to the weeks of gestation starting with the first day of the last menstrual cycle.

***Therefore, for YOUR purposes gestational age will refer in almost all instances to the menstrual age.

-Around 8 weeks and generally up until around 12 weeks, some of the fetal gut can be seen external to the fetus and herniated within the umbilical cord -The three components of the umbilical cord (2 arteries, 1 vein) should be well visualized on ultrasound by 16 weeks.

**Only if there is still herniation into the cord after 12 weeks (usually at 14 weeks) can an abdominal wall defect be diagnosed.

The flickering of the embryonic heart motion can be seen at about the same time the echoes of the embryo can be visualized. **The cardiovascular system is the first organ system to become functional in the embryo.

-***Fetal heart activity is detected consistently by seven weeks with sonography and may be seen as early as 5.2 weeks -It is usually seen at 6 weeks and if it is NOT seen at 7 weeks, the embryo is not viable, (assuming it REALLY IS 7 weeks). Embryonic heart activity should always be seen by 46 menstrual days (6 wks. 4 days).

At 4 to 5 weeks (menstrual age) the choriodecidua that surrounds the gestation can be seen on sonography.

-At 4 weeks it appears as a thickened, lush endometrial echo in the fundus. It would exhibit an area of increased echogenicity on a sonogram. On transvaginal scans prominent arcuate vessels are often seen in the periphery of the myometrium at this time. -At about 4.5 weeks it may be possible to see a 2 - 3 mm gestational sac with high resolution transvaginal scanning. -At 5 weeks the normal sac appears as a rounded anechoic structure (representing the blastocyst), surrounded by a prominent echogenic double ring (representing chorionic villi and decidual reaction).

Cephalic Index The two most frequently seen alterations in head shape are dolichocephaly and brachycephaly.

In dolichocephaly the BPD is shorter and the OFD is elongated - thin, long head. In brachycephaly the BPD is elongated and the OFD is shortened - round head. -Some authors feel that an abnormal CI can be the first indication of impending fetal demise when it changes very quickly.

After implantation of the blastocyst, the HCG level normally increases in an exponential fashion, **doubling every 2 days. (remember this and better still, answer the range of every 2 - 3 days if that is a choice on a test. If you have to choose between 2 and 3 days, choose 2 days)

After 8 weeks the HCG level plateaus and subsequently declines

The embryo grows about 1 mm/day and can be seen as a small group of echoes near the yolk sac (but INSIDE the amniotic cavity) at about 6.5 to 7 weeks transabdominally and about 5.5 to 6 weeks transvaginally

The normal CRL increases about 1 mm/day from 6 - 10 weeks - can be up to 10mm/week from 8 to 12 weeks.

***This secondary yolk sac is the first structure that can be visualized sonographically in the gestational sac. (5 - 5.5 weeks transvaginally; 6 - 7 weeks transabdominally). -The secondary yolk sac is a round echogenic ring with a sonolucent center. It measures about 4 mm in diameter and lies ***outside the amniotic cavity but close to the embryonic echoes when they can be seen. The normal diameter of the yolk sac should not exceed 5.6 mm -Ideally on a test, a range of normals will be given, such as 4 - 6 mm.) -The secondary or "sonographic" yolk sac has essential functions in embryonic development, including: providing nutrients to the developing embryo hematopoiesis (or hemopoiesis) development of embryonic endoderm, which forms the primitive gut

There is a primary yolk sac that predates the secondary yolk sac but this is never seen sonographically because it is too small.

Transvaginally the yolk sac can be seen at 5 to 5.5 weeks.

Transabdominally the yolk sac can be seen at 6 - 7 weeks.