In a woman who conceived after IVF, ovarian hyperstimulation syndrome develops 12 days after embryo transfer and runs a severe, prolonged course. Which mediator distinguishes this LATE form of OHSS from the early form?

• A Exogenous hCG given for final oocyte maturation
• B A spontaneous mid-cycle LH surge
• C Endogenous hCG secreted by the implanting trophoblast ✓
• D Supraphysiologic FSH from continued gonadotropin injections

Explanation

Early OHSS appears within about 9 days of retrieval and is driven by the exogenous hCG bolus used to trigger final oocyte maturation. Late OHSS arises 10 days or more after retrieval, is mediated by endogenous hCG from the implanted pregnancy, and tends to be more severe and protracted because trophoblast hCG production persists and escalates. This is why freeze-all strategies, which interrupt the hCG-driven feedback loop, protect against late OHSS. An endogenous LH surge cannot occur under pituitary suppression, and FSH is not the trigger.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.