So let's discuss pelvic imaging performed during early pregnancy.
Pregnancy is often imaged with the use of ultrasound
because there is no radiation associated with ultrasound.
Ultrasound is the very safe alternative
to other types of imaging during pregnancy.
During first trimester pregnancy,
ultrasound is used for a variety of different reasons.
It includes dating, viability of the fetus, abnormalities of the embryo,
placental abnormalities can be evaluated with ultrasound,
evaluating for ectopic pregnancy in a patient that comes in with pelvic pain
and evaluating for the number of embryos.
Advanced OB ultrasound can also be used in the second and third trimesters.
It can help you detect fetal anomalies.
It can evaluate for amniotic fluid, it can determine fetal position
in a patient where the fetal position is unknown.
And it can also help guide invasive procedures.
So in today's lecture we're gonna be discussing primarily first trimester ultrasound.
So let's review some anatomy before we begin.
So first trimester anatomy includes the presence of an embryo
which we see on this diagram. The embryo surrounded by the amnion,
which contains amniotic fluid, and then the outer layer is the chorion.
We see here the chorionic villi which are seen within the placenta.
There's also the presence of a yolk sac
which we see relatively early in pregnancy.
So let's take a look at these structures on an ultrasound now.
So a gestational sac is the earliest sign of intrauterine pregnancy.
Usually, a yolk sac is also seen very early on so as we see here,
this is the normal appearance of a gestational sac.
This echogenic rim around it is called the normal decidual reaction.
Inside of the gestational sac is this very thin membrane
which represents the yolk sac.
And this is usually visualized between about 3 and 5 weeks of gestation.
The embryo and the fetal heart rate are usually seen
by about 5 or 6 weeks of gestation.
So this is an example of how an ultrasound forms the image of a fetal heart rate.
And you can see here, a normal fetus within a normal gestational sac.
One way to remember this is five alive.
So when the embryo reaches 5 weeks of gestation,
that's when we see the heart rate. The normal fetal heart rate
ranges between about 120 and 160 beats per minute.
So let's take a look at these ultrasound images here,
these are again an ultrasound kind of close up of an embryo within a gestational sac
and you can see the surrounding placenta here.
This is another image of the same thing in a different position
so again you can see the embryo, you can see the surrounding gestational sac
with amniotic fluid and then again the surrounding placenta.
Twin gestation is one of the things that we look for
when we perform our first trimester ultrasound,
so this is just an example of a twin gestation.
We have an embryo here which is labelled embryo A
and then we have another embryo here labelled embryo B.
This is again normal placenta and the normal gestational sac with amniotic fluid.
So the presence of two or more embryos within an endometrial cavity,
represents a twin gestation.
So let's take a look a little bit further at the different types of twin gestation.
So twin gestations, the different types of twin gestations
are based on when cleavage occurs at the time of gestation.
So early cleavage, occurring at days 1 to 3,
results in a dichorionic, diamniotic twin gestation.
Days 4 through 8, so a little bit later on, if the cleavage occurs at that stage
then you have a monochorionic, diamniotic gestation.
A little bit later, so cleavage occurring at the days about 8 to 13,
results on a monochorionic, monoamniotic gestation.
So this is a single sac containing both fetuses.
And very late gestation, cleavage occurring at about days 13 to 15,
actually results in conjoined twins.
So this is obviously very, very rare.
The most common is the dichorionic, diamniotic cleavage
and so you have two completely separate sacs for each of the different embryos.