SHBG showed the strongest prediction for ovulation. Women with high SHBG, independent of testosterone, had higher ovulation rate. In addition, women in high SHBG quartile showed significantly higher conception rate and high pregnancy rate compared with the other quartiles. These findings imply that baseline SHBG level is an independent prediction marker for ovulation in women with PCOS, which further affects conception, pregnancy and even live birth.
High SHBG contributed to high ovulation, conception and pregnancy rates. More subjects should be enrolled to further explore the effect of high SHBG on live birth rate and there may be a probably statistical correlation between live birth rate and SHBG. Previous studies report similar findings on the effect of SHBG. Women with regular ovulation showed statistically higher serum SHBG compared with PCOS women with anovulation 16. A secondary analysis of two trials conducted among PCOS women showed that SHBG is positively correlated with conception, pregnancy and live birth which is consistent with our results7. However, another prospective study comprising 251 infertile women with clomiphene citrate resistant polycystic ovary disease, reports that SHBG is not predictor of spontaneous ovulation within eight weeks after laparoscopic ovarian drilling17. More studies should be conducted to explore relationships between SHBG and reproductive outcomes of PCOS women.
In addition, SHBG is implicated in several pregnant complications. Firstly, SHBG is a marker in predicting GDM in PCOS subjects 18. Moreover, a previous prospective study reports that SHBG is an independent risk factor for PCOS women who had preeclampsia (PE) 19. However, a previous case–control study report that PCOS women with a preeclamptic history have no significant difference compared with normal subjects 20. Additionally, SHBG can be used as an integrative biomarker in prediction for adverse cardio-metabolic profile in pregnant women with pregestational plus gestational obesity. SHBG levels, independent of BMI and other metabolic and endocrine variables, are associated with c-reactive protein and systolic blood pressure 6. These findings imply that low SHBG level of PCOS women is correlated with low pregnancy rate, live birth rate and a high incidence of several pregnant complications which have adverse effects on both maternal and child health. PCOS women have significantly lower serum SHBG level compared with normal women 21. Therefore, if PCOS women with lower SHBG desire to have children, they should take measures to elevate SHBG levels thus increasing ovulation rate. Increase in ovulation rate will affect conception, pregnancy and delivery.
In addition to treatment, baseline SHBG, showed high predictive ability for ovulation compared with other baseline serum parameters (Fig. 1). SHBG level in higher quartile showed higher ovulation rate after adjustment for testosterone. Testosterone and estradiol had no effect on ovulation rate. Therefore, prediction of ovulation by SHBG is independent of testosterone and estradiol. Most previous studies report on relationships between other sexual hormones and ovulation. Patients with high FSH/LH ratio showed fewer mature oocytes aspirated, indicating that high FSH/LH ratio might has negative effects on follicular development 22. Urinary FSH peak 23 and kisspeptin surge in serum and urine 24 are useful biomarkers for predicting the day of ovulation. Premature ovulation rate is positively correlated with preovulatory E2/−1E2 ratio and premature LH surge 25. A previous prospective study reports that the surge in serum and urinary LH are associated with ovulation 26. Moreover, LH level between 25–30 MIU/ml tested before day 7 of the menstrual cycle showed the strongest prediction for ovulation 27. A prospective trial reports that ovulatory women with PCOS, showed significantly lower anti-mullerian hormone (AMH) and antral follicle count after using clomiphene citrate and highly purified FSH, compared with anovulatory women with PCOS after undergoing the same intervention 28. PCOS women with reduced response to ovulation showed higher AMH 29. Oocyte in-vitro maturation treatments showed that AMH can be used to identify women candidate with suitable number of oocytes 30. However, our findings show that SHBG has higher predictive ability for ovulation compared with other parameters.
Quartiles of SHBG, T and E2 were further calculated and adjusted analyses were performed due to the interaction between SHBG and T and E2. Higher SHBG was positively correlated with higher ovulation rate. Notably, this correlation was statistically significant after adjustment for T, whereas this trend was not observed for T and E2. Therefore, the prediction of ovulation using SHBG levels is independent of testosterone and estradiol. This is consistent with previous findings that SHBG has a stronger prediction value compared with T and E2. A previous polymorphism study conducted on PCOS patients who underwent IVF-ET (in vitro fertilization‐embryo transfer) reports that SHBG rs6259 GA + AA genotype carriers show decreased number of retrieved oocytes and embryo, and fertility rate [= (number of fertilized eggs/number of retrieved oocytes) × 100%] 31. Further, high-molecular-weight adiponectin level is positively correlated with SHBG 32. Adiponectin modulates follicular growth and maturation33, therefore, correlation between adiponectin and follicle showed be further investigated. A previous study reports that granulosa cell proliferation is increased in anovulatory PCO compared with both normal and ovulatory PCO 34. In addition, AQP-9 mRNA levels in granulosa cells of patients with PCOS were significantly correlated with SHBG levels in follicular fluid35. Therefore, further studies on the correlation between granulosa cell and SHBG should be conducted.
The present study is based on a large multi-center, randomized, double-blind, placebo-controlled design with a representative sample of PCOS population to explore and demonstrate the correlation between SHBG level with reproductive outcomes, including ovulation, conception, pregnancy and live birth. Meanwhile, higher baseline SHBG is associated with higher ovulation rate and is an independent predictive marker.
There are limitations of this study. First, this study is a secondary analysis of PCOSAct. The study does not include certain data, such as data of normal controls. Second, the relationship between SHBG and ovulation for each menstrual cycle was not determined. Besides, larger samples are needed to certify that high SHBG statistically associated with high live birth.