MCA-PSV for suspected fetal anemia
Use this calculator to estimate the expected median MCA peak systolic velocity for gestational age and to compute
multiples of the median (MoM) . MCA-PSV is widely used as a noninvasive screening test for moderate or severe fetal anemia,
commonly using 1.5 MoM as the action threshold
MCA Peak Systolic Velocity Calculator
Enter gestational age and the observed MCA peak systolic velocity (PSV) to compute the expected median PSV, MoM, and plot the result on the graph.
Quick info, images, and limitations
MCA-PSV may be used to help evaluate suspected fetal anemia in settings such as red blood cell alloimmunization, parvovirus infection, fetomaternal hemorrhage,
alpha-thalassemia, placental chorioangioma, and selected twin complications including twin anemia-polycythemia sequence when clinically appropriate.
In fetal anemia, reduced blood viscosity and increased cardiac output
result in faster cerebral arterial blood flow; therefore the peak systolic
velocity in the middle cerebral artery rises. A value of ≥1.5 multiples of
the median (MoM) on repeat testing is used as a threshold for possible
intrauterine transfusion.
A commonly cited strength of MCA-PSV screening is its high sensitivity for moderate or severe fetal anemia using a threshold of
1.5 MoM . However, false-positive results do occur , and they become more common in later gestation, particularly after
about 35 weeks .
False positives and practical interpretation
Why false positives occur: suboptimal insonation angle, fetal breathing or movement, transient physiologic variation, late gestation, and clinical situations in which cerebral blood flow is increased without clinically important anemia. A single elevated value does not always equal true moderate or severe anemia.
Interpret MCA-PSV together with the clinical indication , ultrasound findings, and trend over time.
Results in the late third trimester deserve extra caution because specificity is lower.
A borderline or unexpected elevation may justify repeat or confirmatory Doppler rather than immediate invasive testing in selected cases.
After prior intrauterine transfusion, performance characteristics may differ from non-transfused fetuses.
When this page helps most
To quickly convert a raw MCA-PSV into a gestational-age-adjusted MoM .
To explain visually why the same raw PSV may be normal at one gestation but abnormal at another.
To support consistent interpretation among clinicians, sonographers, and staff.
References
These references support the use of middle cerebral artery peak systolic velocity (MCA-PSV)
as a noninvasive screening test for fetal anemia, the common use of a threshold of
1.5 multiples of the median (MoM), and the caution that false-positive results increase
in late gestation.
Mari G, Deter RL, Carpenter RL, et al.
Noninvasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization.
N Engl J Med . 2000;342(1):9-14.
doi:10.1056/NEJM200001063420103.
PMID: 10620643.
Landmark study establishing MCA-PSV as a noninvasive method for detecting moderate or severe fetal anemia.
This is the foundational paper behind the widespread use of the 1.5 MoM threshold.
Mari G.
Middle cerebral artery peak systolic velocity for the diagnosis of fetal anemia: the untold story.
Ultrasound Obstet Gynecol . 2005;25(4):323-330.
doi:10.1002/uog.1882.
PMID: 15789353.
Important review discussing clinical use of MCA-PSV and noting that false-positive results become more frequent
after approximately 35 weeks of gestation.
Mari G, Norton ME, Stone J, Berghella V, Sciscione AC, Tate D, Schenone MH; Society for Maternal-Fetal Medicine (SMFM).
Society for Maternal-Fetal Medicine (SMFM) Clinical Guideline #8:
the fetus at risk for anemia—diagnosis and management.
Am J Obstet Gynecol . 2015;212(6):697-710.
doi:10.1016/j.ajog.2015.01.059.
PMID: 25824811.
Core guideline reference for diagnosis and management of the fetus at risk for anemia.
Supports MCA-PSV as the primary noninvasive screening tool in appropriate clinical settings.
Oepkes D, Seaward PG, Vandenbussche FP, et al.
Doppler ultrasonography versus amniocentesis to predict fetal anemia.
N Engl J Med . 2006;355(2):156-164.
doi:10.1056/NEJMoa052855.
PMID: 16837679.
Major comparative study showing that MCA Doppler performed better than amniotic fluid
ΔOD450 testing for prediction of fetal anemia.
Moise KJ Jr.
The usefulness of middle cerebral artery Doppler assessment in the treatment of the fetus at risk for anemia.
Am J Obstet Gynecol . 2008;198(2):161.e1-4.
doi:10.1016/j.ajog.2007.10.797.
Practical clinical review emphasizing how MCA-PSV is used in management and noting that
false-positive rates increase after 35 weeks.
Maisonneuve E, Doret-Dion M, Brossard Y, et al.
Accuracy of middle cerebral artery Doppler assessment between 34 and 37 weeks in fetuses at risk for anemia.
Am J Obstet Gynecol . 2017.
PMID: 28278506.
Useful later-gestation accuracy study, especially relevant if you want literature support on
reduced test performance and interpretation challenges beyond 34 weeks.
Richards DS, Grindheim G, McCullough LB, et al.
Confirmatory middle cerebral artery Doppler testing in patients with suspected fetal anemia.
Am J Perinatol . 2024.
PMID: 35709735.
Recent paper supporting repeat confirmatory Doppler assessment in selected cases because
false-positive MCA-PSV results are common and a repeat examination may reduce unnecessary invasive testing.
Mari G, Hanif F, Kruger M, Cosmi E, Santolaya-Forgas J, Detti L.
Middle cerebral artery peak systolic velocity:
a new Doppler parameter in the assessment of growth-restricted fetuses.
Ultrasound Obstet Gynecol . 2007;29(3):310-316.
Helpful background reference on physiologic interpretation of elevated MCA velocities and
cerebrovascular adaptation, though not limited to alloimmunization.
Abbasi N, Johnson JA, Ryan G.
Fetal anemia.
Ultrasound Obstet Gynecol . 2017;50(2):145-153.
doi:10.1002/uog.17555.
PMID: 28782230.
Concise review of causes, diagnosis, and management of fetal anemia with practical discussion
of MCA-PSV screening.
Anabusi S, Van Mieghem T, Ryan G, Shinar S.
Elevated Middle Cerebral Artery Peak Systolic Velocity in Non-Anemic Fetuses: Providing a Better Understanding of Enigmatic Middle Cerebral Artery Peak Systolic Velocity. Fetal Diagn Ther. 2024;51(6):550-558. doi: 10.1159/000540342. Epub 2024 Jul 18. PMID: 39025054; PMCID: PMC11633866.
Concise review of causes, diagnosis, and management of fetal anemia with practical discussion
of MCA-PSV screening.
MCA-PSV is a sensitive noninvasive screening test for moderate or severe fetal anemia.
A value of ≥ 1.5 MoM is commonly used as the threshold for concern.
However, false-positive results occur, particularly after about 35 weeks ,
so abnormal values should be interpreted with technique, clinical context, and repeat or
confirmatory testing when appropriate.
Author: Mark Curran, MD FACOGPage concept: calculator + graph + literature-based interpretationLast reviewed: March 2026
