First Trimester Foundation: The Five A’s

First, it is important to know and understand the Five A’s and why they are so important. 

The Five A’s are:

  1. Assess
  2. Alive
  3. Alone
  4. Age
  5. Anomalies

When assessing, we are confirming that the pregnancy is intrauterine with a sweep showing that the gestational sac is in the uterus and is surrounded by plenty of myometrium on all sides.  At the same time, we want to be sure the fetus is alive or viable.  Can you see cardiac flicker or motion? Next, we will determine if the fetus is alone.  Are there multiples?  There could be more than one gestational sac or there may be more than one embryo in a single sac.  These are important details to note during the sweep.  Age is determined by measuring the crown-rump length or CRL.  Finally, are there any anomalies?  This could be maternal or fetal.  Fibroids and uterine anomalies are often missed when no sweep is performed. 

The Five A’s provide a framework or workflow of sorts to help you navigate the first trimester ultrasound.  By performing full sweeps of the uterus and/or pelvis, we get a broad view and are less likely to miss multiples, anomalies, etc…

In the case study below, you will see how I navigate a first trimester ultrasound by utilizing the five A’s.

Case Study

Patient presented as a 24-year-old, G1 with a positive pregnancy test and LMP of 3.25.24 which dated the pregnancy at 7w1d. The exam began transabdominally. Starting the exam transabdominally gives the practitioner a broad overview of the pelvis. I obtained both sagittal and transverse views of the uterus and performed a sagittal sweep through the uterus.

Assess

Here you can see that this is an anteverted uterus. There is an intrauterine pregnancy within the uterus and the uterus is a normal size with no evidence of fibroids or other abnormalities.  On the sweep obtained during the abdominal scan, we could see that the embryo is alone, and we were also able to catch cardiac motion.

Alone

Upon inserting the probe vaginally, you can see the sagittal uterus with the gestational sac at the fundus. Once this view is achieved, it is important to sweep right and left to fully evaluate the uterus.

Alive

Once we have the fetal pole into view, you may zoom up and evaluate the fetus.  Above is an M-Mode tracing of the fetal heart rate at 147bpm which is normal. Remember that we should be using M-mode in the first trimester. However, when you are unable to see any motion, it is best to use PW and even color Doppler to be certain. A cine clip showing lack of motion is suggested as well.

Age

Below, you can see two measurements of the CRL here.  Three were performed total as should be the standard, however, I wanted you to see that I was attempting the CRL from different angles to be sure we have the longest length of the fetal pole for measuring.

Anomalies

An evaluation of the adnexa is included in the first trimester ultrasound exam. The images of the left ovary below demonstrate a normal left ovary with a 2.1cm corpus luteum.

The right ovary is also normal.  No adnexal masses were seen.

Report Page

Below is our report page that shows the fetal pole measures on track or consistent with the LMP.  This is a normal first trimester scan.

As we discussed, you can see how important the Five A’s are to the practitioner during a first trimester ultrasound.  Remember to perform sweeps of the uterus and adnexa to assess and then determine if the embryo is alive and alone and whether any anomalies are seen.  Measure the CRL three times to determine gestational age.