normal 1st trimester scanning basics

__________ Age: Counted in days from conception or the day of fertilization. Usually ONLY truly known with cases of _______________

Conceptual, ART (Assisted Reproductive Technologies), like IVF (In Vitro Fertilization) or GIFT (Gamete Intra-Fallopian Tube transfer)

___________ Age: Expressed in weeks from first day of the patients last menstrual period or LMP. Ovulation can occur + 8 days from mid cycle.

Gestational

what is the most common dating method for pregnancies

gestational age

what is the most accurate dating method in the 1st trimester?

CRL (crown rump length (US))

how accurate is dating with IVF?

+/- 1 day

how accurate is dating with ovulation induction and with artificial insemination?

both are +/- 3 days

how accurate is dating with basal body temperature?

+/- 4 days

how accurate is dating with first trimester physical exam?

+/- 14 days

how accurate is dating with second trimester physical exam?

+/- 28 days

how accurate is dating with crown rump length?

+/- 5 days

how accurate is dating with gestational sac measurement?

+/- 7 days

how long is a pregnancy (from LMP assuming the patient has a normal 28-day cycle)?

Approximately 280 days or 40 weeks

what does EDD or EDC mean?

estimated due date or estimated date of confinement

how is the estimated due date or estimated date of confinement calculated? (she said we do NOT need to know this but just incase)

subtracting 3 months from the first day of the patient's LMP then adding 1 year and 7 days (use pregnancy wheel to calculate)

length of the first trimester

0-13 weeks 6 days

length of the second trimester

14 weeks 0 days - 27 weeks 6 days

length of the third trimester

28 weeks 0 days - delivery

what does full term mean?

delivered 37-40 weeks

what does preterm mean?

delivered before 37 weeks

what does post dates mean?

delivered at 40-42 weeks

what does post term mean?

delivered after 42 weeks

does gravida # include the current pregnancy?

yes

How many times they've ever been pregnant (including current pregnancy) is called what?

gravida

The number & types of pregnancies they've had is called what?

para

what is the order/code for the Gs and Ps

G#PFPAL

G, number of times pregnant, P, full term births, preterm births, abortions (spontaneous or induced), living children

what does this mean: G1 P0010

Pregnant 1 time, with 1 miscarriage/abortion

what doe this mean: G3 P1102

Currently pregnant, 1 full term, one preterm (both living)

what does this mean: G1 P2002

Pregnant 1 time, full term twins

what does this mean: G7 P3033

Currently pregnant, 3 full term, 3 miscarriages/ab's, but the 3 full term are living

what does this mean: G3 P1101

Currently pregnant, 1 full term/living child, 1

preterm with probable loss

where baby will live within the uterus

gestational sac

what is the first thing seen on ultrasound

gestational sac

when should the gestational sac first be seen? what should it measure at this point?

4 weeks, 2 mm

how much should the gestational sac grow each day?

1 mm

what must be seen within the gestational sac to confirm there truly is an intrauterine pregnancy?

a yolk sac

what is the gestational sac referred to before a yolk sac is seen within?

a "sac-like-structure"

when only a GS is seen and it is too early to see an embryo, what should hCG levels be around?

1000-2000 mlU/mL, will have patient draw hCGs and repeat scan in 11-14 days

the sonographic measurement of the gestational sac

MSD or mean sac diameter

the MSD is typically measured when a ___________ is NOT present

fetal pole

how much should the MSD increase per day?

~1 mm

formula for MSD

MSD (in mm) = L + W + H / 3

A normal MSD (in mm) + ____ = ~days of pregnancy (she said we do NOT need to know this formula, but just incase)

30

what is the second thing we see in a pregnancy?

the yolk sac

around when do we first see the yolk sac?

5 weeks

what is the function of the yolk sac?

Helps provide nutrients, blood formation, and early development to the digestive & reproductive systems

where is the yolk sac located?

on the outside of the amnion (between the amnion and chorion)

As the pregnancy grows, _______ will get pushed out further, getting essentially squished, sometimes remnants can be found on the placenta

the yolk sac

what is the normal size for a yolk sac?

< 6mm inner to inner

other names for the vitelline duct

Omphalomesenteric Duct or Yolk Stalk

what does the vitelline duct contain?

an artery and vein

what is the function of the vitelline duct?

Transports early blood elements, nutrients and primordial sex cells from yolk sac to embryo

what does the vitelline duct connect?

Connects yolk sac to the embryo's primitive gut

when is the vitelline duct usually obliterated?

around 8-9 weeks (then placenta takes over)

Outermost extra-embryonic membrane

the chorionic membrane

The membrane that surrounds the embryo and the amnion

the chorionic membrane

the chorionic membrane arises from ______________ that invade the ___________

trophoblasts, decidua

what does the chorionic membrane give rise to?

the placenta

Innermost fetal membrane

the amniotic membrane

the amniotic membrane forms a sac filled with _________ that will surround the _________

amniotic fluid, embryo/fetus

the amniotic membrane will grow and expand, completely fusing with

the chorionic membrane around what week?

week 14

In the 1st Trimester, amniotic fluid is mostly formed from __________ as it diffuses across the ____________ of the early forming placenta

maternal blood/plasma, intervillous spaces

Fetal urine production begins around _________ weeks and becomes the main source of ___________ production

10-12, amniotic fluid

aside from fetal urine (after 10-12 weeks), what else forms some amniotic fluid?

the placenta

what is amniotic fluid mostly made of? what else does it contain?

Mostly made of water, but contains fetal cells, later possible meconium and vernix

functions of amniotic fluid

• Is a protective buffer

• Allows for fetal growth & movements

• Helps regulate fetal body temperature

when does the umbilical cord form?

during the first 5 weeks

What two ducts form the umbilical cord?

The body stalk and allantoic ducts unite to form the umbilical cord

what vessels make up the umbilical cord?

2 arteries and 1 vein

what is the function of the umbilical artery?

carries deoxygenated blood away from fetus to placenta

what is the function of the umbilical vein?

brings oxygenated & nutrient rich blood from placenta to fetus

what lines the umbilical cord?

the amnion

what thick, protective, gelatinous material surrounds the umbilical cord?

Warton's Jelly

how early can the fetal/embryonic pole be seen?

as early as 5w4d GA

when is the "diamond ring sign" seen?

around 5 wks 4 days

what does the "diamond ring" sign describe?

yolk sac is the ring, the embryo is the diamond sitting on top

We should see fetal cardiac activity with the fetal pole measures at least ______

7mm (If we don't yet see a FHR at this size, the patient will follow up in 7 days)

The embryo officially becomes a fetus at ____ weeks. This is when ___________ is complete, and everything now just continues to grow and develop

10, organogenesis

how do you measure CRL before a head or butt can be identified?

measure the longest portion of the embryo, end to end

how do you want the baby positioned for CRL?`

a neutral lie (not overly curled up or with the neck hyperextended)

do we include the yolk sac in the CRL measurement?

no

We will measure CRL until the baby measures _______, after will do _________ measurements

84mm, biometry

what do we use to document a fetal heart rate?

M-mode

when can a fetal heart rate be first detected (earliest)?

around 5 ½ weeks

Prior to 6 weeks FHR, can be around _____-_____bpm

90-100 bpm

FHR will reach it's highest around __-__ weeks, around ____-____bpm

9-11 weeks, 170- 180 bpm

FHR will level off after 11-12 weeks and into the 2nd tri, normal range ____-____bpm

120-160 bpm

NEVER use Pulse Wave BEFORE _____ weeks

10

what are some other things to take note of in an early scan?

• Ovaries, where's the corpus luteum?

• Shape and lie of the UT

• Normal early fetal development (the rhombencephalon and bowel/gut herniation)

• Number of gestations, Single vs Multiples

Secretes progesterone to help support the pregnancy until the placenta takes over

corpus luteum

what supports the corpus luteum?

production of hCG

the corpus luteum will regress after about ___ weeks once the ________ shift starts to happen

9, placental

what appearance does the corpus luteum have with color doppler?

"RIng of Fire"

The Rhombencephalon appears as a __________ area at the back of the embryonic head in the early 1st trimester

small cystic

is the rhombencephalon normal to see?

yes

when is the rhombencephalon normally seen?

8 weeks

Bowel starts out too large to fit within the abdomen, so it protrudes into the ____________ around __ weeks

umbilical cord, 8 weeks

bowel will rotate ___° then return into the abdomen around ___ weeks and will rotate again ___°

90º, 12 weeks, 180°

when is it abnormal to see bowel herniation?

after 12 weeks

One fertilized egg that will split into 2 embryos

monozygotic twins

how common are monozygotic twins?

About 1/3 of all twin pregnancies (the less common type of twins)