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This is an ultrasound of a

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normal third trimester pregnancy.

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This is an ultrasound of a normal

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second trimester pregnancy.

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You'll notice that the probe at the skin's

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surface is curved and wide, and transabdominal

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images only were obtained for this patient.

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Often, as the pregnancy progresses,

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transabdominal images alone will be

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sufficient to evaluate the pregnancy.

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So we can see the lower uterus is filled

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with hypoechoic or dark amniotic fluid.

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We also see the fetal head.

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This additional hypoechoic structure

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lateral to the uterus or anterior

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to it is the urinary bladder.

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It's filled with urine.

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And it's important to have the urinary

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bladder distended when imaging a pregnant

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patient transabdominally because the full

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bladder can act as an acoustic window and

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provide higher quality ultrasound images.

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In the second and third trimesters of pregnancy,

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instead of using a mean sac diameter or a crown

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rump length, we'll take specific measurements

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of the fetus to estimate the gestational age.

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This is an example of the biparietal

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diameter, which is a measurement

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that's taken on the fetal skull.

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This is a sagittal transabdominal

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image of the lower uterine segment.

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We can see hypoechoic amniotic

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fluid in the lower uterus, in

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addition to the urinary bladder.

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This is the cervix, and what the sonographer is

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documenting here is that the cervix is closed.

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So this is the canal; this is the internal

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os. It does not have any fluid funneled

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within it, and so this is a closed cervix,

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which is what we're expecting to see.

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The sonographer has also documented the

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location of the placenta as she has visualized it.

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So this hyperechoic structure is the placenta.

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We see this thin, dark line

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posterior to the placenta.

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This is the retroplacental clear

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space; that's a normal finding.

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And then we see uterine myometrium beyond that.

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Another measurement that we will take in the

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second trimester pregnancy is the femur length,

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which is another estimation of fetal age.

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Finally, one of the parameters that we

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can evaluate to estimate gestational

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age of the fetus is the abdominal

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circumference, which we've taken here.

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This is another M-mode tracing

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at the level of the fetal heart.

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You can see again that the sonographer

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has placed the cursor, or the region

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of interest, over the fetal heart.

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And we're seeing rhythmic, equidistant

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deflections of this M-mode tracing.

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We can measure the distance between

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those deflections to estimate the fetal

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heart rate, which for this fetus is 143

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beats per minute, a normal heart rate

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in the second trimester of pregnancy.