Antenatal prophylaxis of Rh isoimmunization: 28-weeks'-gestation service program

Area of Science:

• Obstetrics and Gynecology
• Immunology
• Perinatal Medicine

Background:

• Rh isoimmunization poses a significant risk during pregnancy.
• Antenatal prophylaxis with Rh immune globulin is crucial for preventing Rh disease.
• Previous Rh immune globulin administration protocols varied, impacting efficacy.

Purpose of the Study:

• To evaluate the effectiveness of a single 300 µg intramuscular injection of Rh immune globulin at 28 weeks gestation.
• To determine failure rates of antenatal Rh prophylaxis in different obstetric populations.
• To identify causes of Rh isoimmunization despite prophylaxis.

Main Methods:

• Prospective study of Rh-negative primigravidas and multigravidas receiving antenatal Rh immune globulin.
• Assessment of Rh isoimmunization at 28 weeks gestation and post-delivery.
• Follow-up screening at 6 months postpartum for a subset of participants.
• Comparison of observed failure rates with expected rates if prophylaxis were unsuccessful.

Main Results:

• Only 0.18% of primigravidas/previously treated multigravidas showed isoimmunization at 28 weeks, indicating high efficacy (88%).
• In Rh-negative multigravidas with no prior treatment, 0.42% showed isoimmunization, indicating 75% efficacy.
• Most failures were attributed to prior sensitization or Rh isoimmunization occurring before the 28-week injection.

Conclusions:

• A single 300 µg dose of Rh immune globulin at 28 weeks is highly effective for antenatal prophylaxis.
• Efficacy is highest in primigravidas and previously treated multigravidas.
• Untreated multigravidas have a higher risk, often due to prior sensitization, necessitating careful management.