I.M. per this study. Of course it's one study but I have others if you like
Bioavailability of hCG after intramuscular or subcutaneous injection in obese and non‐obese women
Carina C.W. Chan Ernest H.Y. Ng Maureen M.Y. Chan Oi Shan Tang Estella Y.L. Lau William S.B. Yeung Pak‐chung Ho
Hum Reprod (2003) 18 (11): 2294-2297. DOI:
https://doi.org/10.1093/humrep/deg446
Published: 01 November 2003
Conclusion:
...The AUC and Cmax of hCG in the obese group were significantly lower than those of the non‐obese group, whether hCG was given by either the i.m. or s.c. route (Table I; Figure 1). The AUC and Cmax of hCG were significantly higher after i.m. injection than after s.c. injection in both the obese and non‐obese groups (P < 0.001, Wilcoxon Signed Rank test; Figure 1).
In conclusion, the higher bioavailability of hCG after i.m. injection than after s.c. injection was demonstrated, and a significantly lower bioavailability of hCG was observed in obese women, irrespective of the route of hCG administration. These findings support the advice that obese women should reduce their body weight before embarking on subfertility treatment, as the poor bioavailability of gonadotrophins is one of the many problems that these women might encounter.