A Rh-negative woman at 28 weeks gestation undergoes amniocentesis for fetal karyotyping. She has not yet received antenatal anti-D prophylaxis. How many international units of anti-D immunoglobulin should be administered?

• A 500 IU
• B 250 IU
• C 3000 IU (600 µg)
• D 1500 IU (300 µg) ✓

Explanation

For sensitising events (including amniocentesis) at or after 20 weeks of gestation in Rh-negative women, 1500 IU (approximately 300 µg) of anti-D immunoglobulin is recommended by RCOG and most international guidelines; this dose covers feto-maternal haemorrhage of up to 15 mL of fetal red cells (or ~30 mL fetal blood). The 250 IU dose is used for events before 20 weeks. If Kleihauer-Betke test indicates a larger haemorrhage, a higher dose is required. Routine antenatal prophylaxis is also given at 28 weeks as a separate dose.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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