Protocols for High-Risk Pregnancies. Группа авторов

Protocols for High-Risk Pregnancies

the cardiac structure and flow velocities. Some patients with autoimmune conditions will be SSA/SSB antibody positive and require serial fetal echo for evaluation of P‐R intervals as one indicator of risk for developing complete heart block.

Management of a patient with congenital heart disease should be a collaborative effort with a team consisting of a perinatologist, genetic counselor, pediatric cardiologist, neonatologist, pediatric cardiothoracic surgeon, and the primary obstetrical provider.

Fetal growth restriction

Once the fetus has been diagnosed by ultrasound to be growth restricted, a full ultrasound assessment of the fetus should be performed to exclude fetal anomalies, possible karyotypic abnormalities, and congenital infection. The dating criteria for the pregnancy should be reviewed and estimated date of confinement confirmed. Early‐onset structural abnormalities or symmetrical FGR should result in consideration of excluding karyotype abnormalities and congenital infection.

Treatment options are limited in FGR and include avoidance of physically strenuous activities and work, increased fluid intake, and elimination of adverse social habits such as tobacco, alcohol or recreational drug use. Societal impact of bedrest is significant with an estimated 800 000 patients annually placed on bedrest leading to loss of work and wages. Bedrest should not be recommended as there is no evidence of benefit and there is risk of harm (thromboembolic disease). Avoidance or reduction of physically demanding work and exercise may be reasonable and the patient’s activity level can be labeled as “modified” rest and customized for the patient. In pregnant patients with a history of FGR due to preeclampsia in a previous pregnancy, a baby aspirin (81 mg) has been shown to have some benefit in reducing the risk of recurrence and should be started in the first half of pregnancy, preferably prior to 16 weeks of gestation.

Surveillance of the growth‐restricted fetus includes the use of fetal activity count, serial assessment of fetal growth with ultrasound (every 3–4 weeks), nonstress test and/or biophysical profile, and Doppler velocimetry. Early‐onset FGR fetuses who deteriorate in utero from an acid–base standpoint often demonstrate sequential Doppler changes in different vessels, while these changes occur far less frequently in late‐onset FGR. Use of Doppler in the management of the FGR fetus is further discussed in Protocol 41.

Fetal anemia

The management of fetal anemia requires careful consideration of the etiological factors. The majority of cases will be due to RBC alloimmunization of the mother or parvovirus B19 infection.

Rh sensitization begins with identification of an isoimmunized patient from routine blood type and Rh, and antibody screening tests. When the antibody screen shows the presence of an antibody that places the fetus(es) at risk for fetal anemia, the patient needs to undergo serial screening with antibody titers. An alternative to serial antibody titers that is now more commercially available is the use of cell‐free (cf) DNA to see if the fetus carries the RBC antigen in question. If the antigen is absent in the fetus, no further testing is needed. If the antigen is present, the patient should be followed with antibody titers. Once a critical threshold has been reached by a specific titer of a given RBC antigen antibody, the patient must undergo evaluation for fetal anemia. Most hospital laboratories use either a 1:16 or 1:32 threshold cut‐off and it is essential that each practitioner knows the threshold for their particular hospital or laboratory. Once the critical threshold has been reached, the patient needs to undergo either (i) an amniocentesis for assessment of ΔOD450 in the amniotic fluid or (ii) MCA PSV assessment using pulsed‐wave Doppler velocimetry. If the latter is available, it should receive priority over the amniocentesis simply because it avoids the risk associated with the amniocentesis and has very good performance characteristics as a screening test for moderate to severe anemia. If an amniocentesis is performed and the ΔOD450 is in the high zone 2 or zone 3 of the Liley or Queenan curve, then that fetus must undergo fetal blood sampling for documentation of the anemia and transfusion (see Protocol 42). Alternatively, if the MCA PSV is used to assess fetal anemia, a 1.55 multiple of the median (MoM) value should be used as a threshold above which fetal blood sampling and transfusion are needed.

After one blood transfusion, the MCA PSV loses some accuracy and a different threshold for subsequent transfusion should be used (1.32 MoM has been suggested). The MCA PSV becomes increasingly less reliable for timing of subsequent transfusions and empiric intervals between transfusions are usually used: 7–10 days after the first transfusion, then two weeks until fetal bone marrow suppression is confirmed by Kleihauer–Betke stain and then three weeks thereafter. Administration of phenobarbital (30 mg PO TID) to enhance hepatic maturation can be considered at 34 weeks’ gestation or one week prior to delivery. Delivery of the anemic fetus receiving blood transfusion can generally be accomplished at between 36 and 37 weeks. If fetal blood sampling will be performed at a very preterm gestation, administration of betamethasone should be considered prior to the procedure.

Preterm labor

Use of antiprostaglandin medications such as indomethacin for tocolysis results in inhibition of prostaglandin synthase activity and reduction in prostaglandin synthesis, which may constrict the ductus arteriosus. The effect on the ductus arteriosus is gestational age dependent and generally, indomethacin is not used beyond 32 weeks of gestation. A ductus arteriosus effect is not typically seen within the first 48 hours of treatment. Assessment of the velocity within the ductus arteriosus should be considered beyond that time if the patient continues prostaglandin synthase inhibitor therapy. Constriction is typically reversible with discontinuation of antiprostaglandin drugs.

Summary

Color and pulsed‐wave Doppler velocimetry are useful ultrasound tools for the evaluation and management of fetuses with fetal anemia, growth restriction, congenital heart disease, and fetal arrhythmias. While Doppler ultrasound has been used in other fetal conditions, no study has demonstrated any clear clinical benefit for its use outside those stated above. Widespread use of the DV flow velocity waveforms in the diagnosis of Down syndrome in the first trimester has not yet occurred. Although this is a noninvasive tool to assess for Down syndrome, the emergence of maternal cell‐free fetal DNA screening is far more accurate with extremely high sensitivity for the detection of this chromosomal abnormality. While uterine artery Doppler evaluation of the high‐risk pregnancy might identify a subgroup of women who are at higher risk for adverse pregnancy outcome, the use of Doppler should not be considered a standard medical practice in the general population until further studies demonstrate benefit.

Protocols for High-Risk Pregnancies. Группа авторов