First Trimester Chapter 49 part 1

low hCG level relative to gestational sac development-->a hCG levels fall spontaneously -->b

--> a) abnormal pregnancy -->b) spontaneous future miscarriage concern

what are the decidual layers?

1) decidua basalis (layer closest to the myometrium) 2) decidua parietalis )in the middle) 3) decidua capsularis (innermost)

What would be normally seen at 5 wks?

1-2 mm sac with echogenic ring (ring is the decidual reaction) anechoic center which is the chorionic cavity

when does blastocyst enter the uterus? // when does implantation into decidua occur?

4-5 days after fertilization/conception // within 12 days from fertilization

when does initial heartbeat occur? at this time, what is the approximate CRL?

5-1/2 to 6 weeks; 3 mm; At that time if CRL is greater than 4 mm, then a heartbeat must be seen for it to be considered a living embryo

when is secondary yolk sac routinely visualized

5-5-1/2 weeks of gestation

when do hCG levels normally plateau and decline once gestation continues to grow

9-10 wks

hCG level 3000 mIU/mL

a normal gestational sac can be consistently demonstrated

where is the fetal pole

actual embryo grows on a stalk just adjacent to the yolk sac where its receiving its nutrients from

fetus

after 10 wks

describe utility of PAPP-A serving as a biochemical marker for down syndrome

at 9-11 wks is strongest biochemical marker for down syndrome; PAPP-A is not sensitive enough on its own, must be used with hCG levels or with sonographic markers

compare amniotic cavity to chorionic cavity

chorionic cavity = gestational sac; inner room is the amniotic cavity. The amnion is found on the innermost part of the placenta. It lines the amniotic cavity and holds the amniotic fluid and the developing embryo. The chorion, on the other hand, is the outer membrane that surrounds the amnion, the embryo, and other membranes and entities in the womb.

What can be the first indication of pregnancy on ultrasound?

decidual reaction

normal IUP < 7 weeks: trend for hCG

doubling of quantitative maternal serum hCG levels every 3.5 days!! If not seen, investigate for lack of IUP and for ectopic pregnancy

zygote

during 12 days after fertilization/conception

describe location/shape of early healthy gestational sac

eccentrically placed, fundal position (on one side or the other), embedded in decidual basalis, round or oval shape, smooth contours, decidual wall thickness > 3mm

when do major internal and external structures develop?

embryo stage, wks 4-10

describe how maternal/placental circulation complex develops

enzymes released by trophoblastic cells create lacunae blood pools in decidua to provide source of nourishment for proliferation

Late first trimester (wks 11/12-end)

fetal anatomy fully developed in late first trimester; look for anomalies of basic shape

WKS 11-12

fetus head is disproportionately larger, one half of CRL; also structures continue to develop

Gestational age

first day of LMP, beginning of gestation; used by sonographers; aka menstrual age

embryo shapes

flat disc structure bilaminartotrilaminar,to C shape, which allows for CRL measurement (should be 35 mm by end of 10 wk

Describe triple screen/quad screen. What is the purpose?

free beta subunit-hCG, AFP, PAPP-A, unconjugated estradiol to screen for aneuploidy

embryo

from implantation at about day 28 (wk 4) until 10th wk gest.

how do we calculate gestational age from conceptual age?

gestational age is 2 weeks prior to conceptual age, so it should be 2 weeks more (add 2 weeks)

trend for hCG levels for trisomy 21

hCG levels plateau later and fall much more slowly

what is the source of light spotting in early pregnancy

implantation process, would occur at about the same time as expected MP

what is the normal trend for maternal serum PAPP-A as gestation advances pregnancy-associated plasma protein-A (PAPP-A)

increases

describe double decidual sac sign

interface b/w decidua capsularis and echogenic highly vascularized decidua on opposite wall of endo. cavity forms double decidual sac sign, reliable sign of early IUP (hollow inside is the chorionic cavity)

most dangerous location for ectopic pregnancy

interstitial portion of fallopian tube, around the cornua

trend for trisomy 21 pregnancies with PAPP-A

levels initially lower than in normal pregnancies

trend with ectopic pregnancies regarding hCG levels

lower hCG levels than 3000 mIU/mL (limited absorption outside of the uterus)

Define conception

moment of fertilization; used by embryologists

secreted by corpus luteum after the mature ovum is released

progesterone and estrogen

Name the first gestational structure seen in gestational cavity; it can form at about 23 days (so even before implantation occurs)

secondary yolk sac

Function of hCG

stimulates maternal pregnancy responses; uterine endometrium to convert to decidua, glycogen rich mucosa that provides nourishment during early pregnancy

how long is secondary yolk sac seen

throughout first trimester

which cells secrete hCG?

trophoblastic cells

Standard measurements

when MSD >12 mm, yolk sac should be seen; when MSD >18 mm, embryo should be seen; gestational sac growth occurs at rate of 1 mm/day

blastocyst

when morula has replicated and hollowed itself out; contains inner cell mass, fluid in cavity, and trophoblastic cells lining the structure; forms embryo

morula

when zygote has replicated and becomes 16 cells