Ideal lag time from ovulation to oocyte aspiration using a GnRH agonist trigger

In ART, oocyte maturation (M2) and ovulation is stimulated by a hormonal trigger. For maturation to occur, sufficient "lag time" must elapse between the trigger and aspiration, ranging from 32 to 38 hours. Premature aspiration can result in poor yields; late aspiration risks spontaneous ovulation.

Our study examines optimal lag time using a GnRH antagonist protocol and GnRH agonist trigger for ICSI.

We analyzed data from 220 women undergoing GnRH antagonist protocol using a GnRH agonist trigger for ICSI at our clinic between 02/2012-03/2018. Patients were divided into 4 groups based on lag time: 34.00-34.99 hours (n = 32), 35.00-35.99 hours (n = 113), 36.00-36.99 hours (n = 57) and 37.00 h or more (n = 18). Analyses were performed with the Kruskal-Wallis test, Chi-Square, and Spearman's rho correlation.

A positive correlation was found for the number of M2 oocytes aspirated and lag time (ρ = 0.138, p = 0.04) and for the total number of oocytes aspirated and lag time, (ρ = 0.174, p = 0.01). No correlation was found between the proportion of M2 oocytes aspirated and lag time (p = 0.217). The third group (36 h) had significantly more M2 oocytes aspirated than the second group (35 h) (12.4 ± 7.1 vs 9.4 ± 6.2; p = 0.039). The four groups did not differ for the proportion of mature M2 oocytes (H = 2.453, p = 0.484). The four groups differed in the frequency of live births per fresh embryos transferred (χ² = 9.364, p = 0.025).

Our study identified a positive correlation between lag time and both the number of M2 oocytes and the total number of oocytes aspirated-factors which lead to an increased rate of successful pregnancies. Further research is necessary.