Mca Calculator - Doppler MoM and Anemia Flag

The mca calculator is a fetal medicine screening tool that turns a middle cerebral artery Doppler reading into a gestational-age-adjusted Multiple of Median. The result sits next to the SMFM 1.5 MoM anemia flag, so a clinician can see at a glance whether the Doppler reading has crossed the threshold that should trigger further evaluation. It is built on the 2000 Mari reference curve, which is still the underlying model behind the SMFM Clinical Guideline #8 for fetal anemia work-up.

• • Confirm an MCA Doppler reading at a routine anatomy scan: enter the gestational age and the peak systolic velocity the sonographer wrote on the report and the calculator will show whether the reading is on, above, or below the median for that week.
• • Track a pregnancy flagged for alloimmunization or parvovirus: rerun the calculator every time a new Doppler reading is taken in a pregnancy at known risk, and watch the MoM track between the borderline and moderate-or-severe bands.

MCA stands for the middle cerebral artery, the largest of the three vessels that supply the fetal brain with blood. Its peak systolic velocity rises with gestational age in a way that is reproducible across ethnic groups, which is why the 2000 Mari reference curve is still in use.

The calculator does not perform the Doppler scan. The clinician or sonographer measures the peak systolic velocity in cm/s, the calculator takes that number and the gestational age, and the result is the Multiple of Median plus the SMFM anemia band.

For pregnancies where the gestational age is not already pinned down from a dating scan, the Gestational Age Calculator will give the same completed-weeks input the mca calculator expects, before the Doppler reading is added.

The mca calculator plugs the gestational age into the Mari 2000 natural-log linear model, exponentiates the result to get the median peak systolic velocity in cm/s, and divides the Doppler-measured reading by that median to get the Multiple of Median.

• gestationalAge: Gestational age in completed weeks from 14+0 to 40+6. The reference curve was validated in this window.
• measuredMCA: Peak systolic velocity of blood flow in the fetal middle cerebral artery, measured in cm/s.
• medianMCA: Expected median peak systolic velocity in cm/s, computed from the Mari 2000 equation.
• MoM: Multiple of Median. The measured PSV divided by the median PSV. A value of 1.00 sits on the median.

The natural-log linear model in the original Mari paper is the same one used inside the calculator, so the median moves the same way it does on the published reference curve.

The risk band uses the four-band SMFM grouping: a MoM below 1.29 is labeled low, 1.29 to 1.49 is borderline, 1.50 to 1.54 is moderate or severe, and 1.55 or higher is severe.

According to Mari et al. (Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses, NEJM 2000), the median fetal middle cerebral artery peak systolic velocity follows ln(PSV) = 2.31 + 0.046 x GA, validated in 111 at-risk fetuses with a sensitivity of 100 percent for moderate or severe anemia.

When the Doppler report only shows the estimated due date and not the gestational age in completed weeks, the Pregnancy Due Date Calculator converts the due date into the same completed-weeks input the median PSV needs.

Four ideas carry the result.

The 1.5 MoM threshold is what prompts further evaluation for fetal anemia, so the calculator exposes the threshold as a dedicated flag rather than burying it in a generic risk label.

Because the same Doppler suite also reports estimated fetal weight, the Fetal Weight Percentile Calculator shows the percentile the sonographer would expect for the same gestational age, which is the next number to look at when the MoM is borderline.

Two numeric fields and one clinical-context field are enough to populate the result panel.

1. 1 Enter the gestational age in completed weeks: use the same gestational age the sonographer wrote on the Doppler report. The Mari 2000 reference was validated between 14 and 40 weeks.
2. 2 Enter the measured MCA peak systolic velocity in cm/s: the value on the Doppler report, in cm/s. Values from 5 to 120 cm/s cover the validated range; readings outside that window almost always reflect a measurement or input error.
3. 3 Pick the pregnancy type for the disclaimer: the Mari 2000 model was built from singleton pregnancies. A twin pregnancy still produces a median and a MoM, but the result needs to be read by a maternal-fetal medicine specialist.
4. 4 Read the MoM before the band: the result panel shows the median PSV, the MoM, the risk band, and the 1.5 MoM flag in that order. The band is a coarse label; the MoM is the number to discuss with the specialist.
5. 5 Check the 1.5 MoM flag before sharing the result: the dedicated flag mirrors the SMFM threshold. A reading at or above 1.5 MoM is the trigger for further evaluation, not a confirmed diagnosis.

A sonographer writes a peak systolic velocity of 47.5 cm/s at 32 weeks in a singleton pregnancy flagged for maternal alloimmunization. The user enters gestational age 32, measured PSV 47.5, and singleton. The calculator returns a median of 43.9 cm/s, a MoM of 1.08, and a low anemia risk band, so the next step is a repeat Doppler in one to two weeks rather than an immediate referral.

When the user only knows the last menstrual period or the conception date, the Pregnancy Calculator produces the same gestational age the mca calculator needs, so the same Doppler reading can be re-entered without re-measuring anything.

Using the mca calculator as the second step in a fetal anemia work-up gives a clear numeric anchor to the same SMFM 1.5 MoM threshold the guideline uses.

• • Same reference curve as the SMFM guideline: the median PSV comes from the Mari 2000 natural-log linear model, which is the underlying reference for SMFM Clinical Guideline #8 and most perinatology textbooks.
• • MoM and 1.5 MoM flag side by side: the result panel shows the MoM and the 1.5 MoM anemia flag in the same view, so a clinician does not have to do the mental math against the published table.
• • Twin pregnancy disclaimer baked in: a twin pregnancy entry adds the perinatology disclaimer, because the Mari 2000 reference was built from singleton pregnancies and the MoM cutoffs differ in twin-twin transfusion.
• • Visible arithmetic, not a hidden number: the median PSV is shown alongside the measured PSV, so the user can see the denominator behind the MoM and verify the result against the Doppler report.
• • Screening reference, not a diagnosis: every result ends with a clinical note that the MoM is a screening reference and that any reading at or above 1.5 MoM should be discussed with a maternal-fetal medicine specialist.

The result depends on the Doppler measurement technique and the assumptions built into the reference. Four small changes can move the risk band by a step, especially when the MoM sits near a cutoff.

• • The mca calculator implements the Mari 2000 reference curve between 14 and 40 weeks only. Gestational ages outside that range are clamped and the band is suppressed.
• • The MoM is a screening reference, not a diagnosis. Moderate or severe fetal anemia is confirmed by cordocentesis, and a MoM at or above 1.5 is the trigger for further evaluation, not the final answer.
• • The 1.29, 1.5, and 1.55 MoM cutoffs were validated in pregnancies at risk for alloimmunization. They have different sensitivity and false-positive rates in parvovirus B19 infection, twin-twin transfusion, and other causes of fetal anemia.

According to Society for Maternal-Fetal Medicine (SMFM) Clinical Guideline #8, a fetal middle cerebral artery peak systolic velocity at or above 1.5 multiples of the median is the threshold that should prompt further evaluation for moderate or severe fetal anemia.

According to Mari and Abuhamad (2005), a correct fetal middle cerebral artery Doppler measurement requires the probe beam to be aligned with the direction of blood flow and the sample volume placed within 2 mm of the internal carotid artery origin.

Twin pregnancies carry a different reference curve for MCA Doppler, and the Twin Pregnancy Weight Gain Calculator is a quick way to check whether the weight-gain trajectory for the same twin pregnancy is on the expected track at the same gestational age.