Management of

Rh-Sensitized Pregnant Patient Prof. Aboubakr Elnashar Benha University Hospital. Egypt

Aboubakr Elnashar

Any Rh- patient with an anti-D titer >1:4 should

be considered sensitized.

1. Sonogram. At 1st visit

Accurate dating for G age

{interpret fetal tests

timing of fetal interventions}.

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2. Establish Paternal Blood Type. {The pregnancy is at risk only if the fetus has inherited

the D antigen}.

Paternal Ag: {avoid multiple fetal interventions}.

Paternal red cell phenotype

•If Rh-: the fetus will be Rh- and not at risk: No further

intervention.

•If heterozygous for D: the fetus has a 50% chance of

being at risk.

•If homozygous: the fetus will be at risk for hydrops.

All fetuses must be assumed to be Rh+ until proven

otherwise.

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3. Follow Serial Maternal D Antibody

Titer. Critical titer:

The titer at which fetus is at risk

1:16 or

An increase of >1 dilution (e.g. 1:2 to 1:8). Once the maternal antibodies surpass the critical titer:

further titers will no longer be helpful

serial fetal testing will be required throughout the remainder of

the pregnancy.

Correlation between titer and severity of disease: poor.

But: significant hemolytic disease

Elevated antibody titers at the beginning of pregnancy

rapid rise in titer

titer of 1 : 64 or greater,

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4. Serial Fetal Assessment. Aim: Determine timing of intervention.

a. Amniocentesis.

Serial beginning at 24 to 26 w {determine the

likelihood of fetal anemia}.

Amniotic bilirubin 2ndry to fetal hemolysis

was directly proportional to the

spectrophotometric peak at 450 nm (OD450) (Liley, 1961).

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Zone 1: The fetus is unlikely to be affected at this time, or only

mildly affected: repeat amniocentesis in 10 to 14 days.

Zone 2: The fetus is experiencing mild-to-moderate hemolysis.

lower zone (>80%): amniocentesis in 10 to 14 days

upper zone(<80%): fetal blood sampling

Zone 3: The fetus is anemic. A high probability of fetal death is

present in 7 to 10 days unless intervention occurs: fetal

blood sampling

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Fetal blood sampling (Hct<30%):

<35 w: intrauterine transfusion

>35 w: delivery

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b. Middle cerebral artery peak systolic velocity (MCA-

PSV)

The most significant breakthrough in the surveillance of

the potentially anemic fetus

Based on:

In fetal anemia:

Enhanced fetal cardiac output and

Decrease in blood viscosity:

Increased blood flow velocity

preferentially shunt blood to brain faster

most pronounced MCA PSV

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Frequency

•Initiated: as early as 18 w

•Repeated: every 1–2 w as the clinical situation

warrants.

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Steps:

A transverse view of the fetal brain is obtained at the

level of BPD. The transducer is then moved caudally to

demonstrate the thalamus clearly.

With color flow imaging MCA can be identified as the

major anterolateral branch of the Circle of Willis.

The pulsed Doppler sample gate should be placed at

the junction of the medial third and middle third of this

artery

Pulsed Doppler is then used to measure MCA-PCV just

distal to its bifurcation from the internal carotid artery. The angle of insonation is invariably small due to the usual occipitotransverse

position of the fetal head.

Since the MCA-PSV is a measurement of absolute instead of relative velocity,

the angle of the fetal Doppler insonation should be kept as close as possible to

0˚ for accurate estimate of the absolute peak systolic flow velocity.

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Power Doppler with visualization of the Circle of Willis and the Middle cerebral artery.

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Normal flow of the MCA in 1- st trimester

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Normal flow of the MCA in 2 and 3 trimester.

Flow velocity wave form in the fetal MCA in a normal fetus at 22w Aboubakr Elnashar

Top. Color Doppler waveform obtained from the middle cerebral artery in a normally grown fetus at 34 weeks. Bottom. Measurements are obtained using the maximum frequency follower. Aboubakr Elnashar

Interpretation

{MCA velocity increase with advancing gestational

age} results are reported in MoM.

The actual value can be plotted on standard curves or

entered into a website that will calculate the MoM value

(www.perinatology.com).

A value greater than 1.5 MoM: moderate to severe f

anemia: further investigation through direct ultrasound-

guided fetal blood sampling (cordocentesis)

After 35 w: false positive rate for the prediction of f

anemia is increased {fetal heart rate accelerations}

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The solid curve indicates the median MCA-PSV The dotted curve indicates 1.5 multiples of the median.

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MCA-PSV plotted as a function of gestational age. Above the upper line (1.5 multiples of the median): invasive testing and treatment are indicated. Below that line, individual monitoring regimes are established.

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Top: Color Doppler waveform of the MCA. Bottom: The maximum frequency follower has been used to calculate the PSV (87.9cm). The value lies above the 95th centile for gestation, making it highly suggestive of fetal anemia. Aboubakr Elnashar

MCA waveforms in an anemic fetus requiring serial transfusions for severe Rh (D) disease. The peak systolic velocities of 62, 50, and 61 cm per second (top to bottom) corresponded to fetal hematocrits of 19%, 44%, and 32%, before, at the time of, and a week after the first intravascular transfusion, respectively.

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Advantage

More sensitive for predicting f anemia than the ΔOD450

(Recent studies) Alternative to serial amniocenteses

Excellent noninvasive tool for the monitoring of f

anemia.

Reduction of over 80% in the need for invasive

diagnostic procedures such as amniocentesis and

cordocentesis.

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An accurate predictor of severe f anemia (II-1A)

(Recent systematic review) Correlation with the fetal hemoglobin value becomes

more accurate as the severity of anemia increases

The correlation between hemoglobin concentration and

the MCA-PSV has rendered amniocentesis for the

measurement of the ΔOD450 an outdated tool

{transfusion therapy should never be initiated without

confirming fetal anemia}.

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Limitations

1. Reliability decreases after 35 w, so alternative

methods must be used.

2. Dopplers can easily be measured incorrectly: should

be performed only by experienced clinicians.

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Flow velocity waveform in the fetal MCA in a severely anemic fetus at 22 w. blood velocity is increased

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Other sonographic findings have been claimed to either precede the development of

hydrops or predict fetal anemia:

amniotic fluid volume

liver and spleen length or thickness

placental thickness

increased bowel echogenicity

cardiac biventricular diameter

none of these are reliable.

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6. Serial NSTs or BPPs Weekly beginning at 32 W.

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6. Delivery.

At 35 weeks:

1. Fetus has required transfusion

2. Abnormal Doppler studies

At 37 and 39 weeks:

If the maternal critical titers were not

reached

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Management of Sensitized Rh-Negative Women

Serial indirect Coombs tests are performed at monthly

intervals after 18 w until the critical titer is exceeded.

• At that time, serial MCA-PSV are performed weekly.

• Cordocentesis is performed when MCA-PSV>1.5 MoM

During the first sensitized pregnancy, the Coombs titer

correlates with the severity of fetal disease. However,

these titers are poorly predictive after the first sensitized

pregnancy. Aboubakr Elnashar

Thank you

Aboubakr Elnashar