In the second trimester, the patient’s uterus is larger
to accommodate the growing fetus and may not be obtained in
one single mid-line image. In order to display the entire
uterus, two images may be required.
The maternal uterus is now larger in order to
accommodate the growing baby. One mid-line
longitudinal image might not provide visualization
of the entire uterus. Two images may have to be
taken. The first image is of the maternal bladder,
vaginal canal, cervix (if seen) and the lower
uterine segment. The image should include the
uterus, baby, and a portion of the placenta.
The second image will include the fundus of the
uterus. Be sure that the margins of the uterus
are evident. Slide the transducer superiorly at
the mid-line. This image should include the
baby, placenta and fundus of the uterus.
Next, scan completely out of the uterus to the
right adnexa and scan in the opposite direction
to scan the left adnexa.
Turn the probe 90 degrees counter-clockwise in order
to image in the transverse plane. Scan inferiorly
towards the vaginal canal (which might be shadowed
out by the baby’s ossified bones). Scan superiorly
through the uterus and maternal bladder. Take the
second image at the widest portion of the uterus to
reveal a portion of the baby and the placenta. Be
sure the margins of the uterus are clearly
visualized.
A bi-parietal diameter is the fetal measurement used
in the limited obstetric- al ultrasound protocol for
the second and third trimester. The image is of the
fetal head at the level of the falx cerebri,
thalamus and the cavum septum pellucidum. Choose the
BPD measurement in the package under the measurement
key. The calipers should be placed on the fetal
cranium from leading edge to leading edge at the
widest portion of the skull.
As in the first trimester scan, a second
image should be taken in order to check for
consistency in dating. Obtain another image
of the baby’s head with the proper landmarks
in the brain visible. Choose the BPD
measurement in the package under the
measurement key and take a second
measurement. Measurements are most accurate
when the fetal cranium appears oval,
landmarks are evident and the babies head is
perpendicular to the sound beam.
The baby is larger in the second and third
trimester and the chambers of the heart are
obvious. For optimal imaging, zoom up on the
fetal heart. Press the mid-line key and choose a
sample area. Ideally, the sample area should be
placed on the portion of the heart valve that
opens and closes the widest. This will provide
the most apparent waveform for the M-mode
measurement. Measure from the beginning of one
beat to the beginning of the next. Print report
page.
