Implications of blood type for ovarian reserve.

BACKGROUND: We explored the relevance of blood type to ovarian reserve, as reflected by early follicular phase FSH levels. METHODS: For this cross-sectional observational study, early follicular phase serum levels of FSH (mIU/ml) and estradiol (E2, pg/ml), and information on blood type (A, B, AB and O) and patient age were procured for female patients, ≤ 45 years age (n= 544), who were undergoing fertility evaluation at one of two tertiary care facilities. Serum FSH > 10 mIU/ml was taken to reflect diminished ovarian reserve (DOR). Data distribution for FSH and age was analyzed and non-parametric tests used for comparisons across blood groups. Multivariable logistic regression analyses determined the relationship between elevated FSH and respective blood types after adjusting for age and study site. RESULTS: Prevalence of blood types according to order of frequency was: O (45%), A (35%), B (16%) and AB (5%). After adjusting for age and study site, patients with blood type O were twice as likely to exhibit FSH > 10 mIU/ml compared with those with A or AB blood types [odds ratio (OR) 2.36; 95% confidence interval (CI) 1.27-4.41; P= 0.007], and three times as likely to manifest FSH > 12 m IU/ml (OR 3.48, 95% CI 1.46-7.32, P= 0.004). The B blood group antigen failed to exhibit any relationship with ovarian reserve as reflected by baseline FSH (P> 0.05). CONCLUSIONS: The A blood group antigen appears to be protective for ovarian reserve, whereas blood type O appears to be associated with DOR, in a relationship that is independent of advancing age. Further studies are needed to establish causality and identify the underlying mechanisms for the association.