Excretory profile of inhibin-like peptide (ILP) during human menstrual cycle: a probable marker for determination of fertile period. 
The excretory profile of inhibin-like peptide (10.4 kDa) and its interrelationship with urinary LH, FSH, oestrone glucuronide (E1G) and pregnanediol glucuronide (PdG) during the menstrual cycle were studied.  These hormones/metabolites were estimated in daily early morning urine samples obtained from 20 regularly menstruating women.  The data revealed that the excretory profile of inhibin-like peptide (ILP) follows a pattern similar to that of E1G. In 17 cycles, ILP peaked 3-4 days prior to the urinary LH peak.  A value of 70 ng/mg creatinine (95th centile of ILP levels obtained between 2 and 4 days prior to urinary LH peak and also 5th centile of peak ILP levels) was considered as an indicator of the start of the fertile period.  A value of PdG more than 2 micrograms/mg creatinine on two consecutive days was considered as an end of the fertile period.  The entire fertile period could be determined in 18 out 20 cycles when criteria based on ILP and PdG levels were applied (accuracy, 90%), whereas it could be determined in 13 out of 20 cycles when criteria based on E1G and PdG levels were applied (accuracy, 65%).  Thus, ILP levels in urine may prove to be one of the signals for determining the start of fertile period.