Whither human IVF? Fertilisable oocytes selected on the basis of follicular temperature

Temperature gradients in the mammalian ovary and genital tract: A clinical perspective

Temperature within mammalian reproductive tissues is noted to be a key component of fertility, and significant gradients in temperature can be demonstrated deep within the abdomen shortly before ovulation. Indeed, in the absence of such gradients in the ovary and genital tract, the processes of ovulation and fertilisation are severely compromised. This review aims to assess literature produced during the last five decades regarding temperature gradients in the mammalian ovary and genital tract. A large body of observations derived from rabbits, women, pigs and cattle is summarised in tabular form, ovarian follicular values being as much as 2.5 °C or more cooler than neighbouring ovarian tissues or deep rectal temperature. We highlight recent works demonstrating a positive correlation between pre-ovulatory follicular cooling and pregnancy. Understanding the significance of follicular cooling should help us (a) explain why so many potential pregnancies fail in vivo as in vitro and (b) inspire ways for improving the processes of fertilisation and establishment of a full-term pregnancy. Based on our findings in domestic animals, and most recently in cows whose Graafian follicles are comparable in size and timing of response to the LH peak with human follicles, we wish to encourage IVF and fertility preservation clinics to take advantage of this work. By so doing, the incidence of full-term pregnancies in women should be improved.

Pre-ovulatory follicular cooling correlates positively with the potential for pregnancy in dairy cows: Implications for human IVF

INTRODUCTION

In rabbits, pigs, cows and humans, pre-ovulatory Graafian follicles may be more than 1.0 °C cooler than ovarian stroma and both these ovarian compartments are cooler than deep rectal temperatures. This study examines the effect of follicular cooling on the incidence of pregnancy in dairy cows.

MATERIAL AND METHODS

Follicular measurements were compiled for cows with one ovulatory follicle (monovular) and cows with one ovulatory follicle per ovary (bi-ovular) and their corresponding uterine horn contents. The study sample consisted of 80 pre-ovulatory follicles in which antral temperatures were measured using a fine thermistor probe.

RESULTS

Mean (± S.D.) follicular fluid temperature of the ovulating follicles was 1.12 ± 0.86 °C significantly cooler (P < 0.0001) than rectal temperatures. No significant differences in temperatures were found for non-ovulating follicles. In follicles undergoing cooling (n = 58), a one-tenth of a degree drop in temperature with reference to control rectal temperature gave rise to a 3.6-fold increase (odds ratio) in the pregnancy rate (P = 0.003). The follicle-rectum temperature differential giving rise to pregnancy (n = 18; 1.51 ± 1.15 °C) was significantly greater (P = 0.004) than the differential recorded in cooling follicles at that did not result in a subsequent pregnancy (n = 40; 0.83 ± 0.57 °C).

CONCLUSION

Follicular cooling is needed to trigger ovulation and correlates positively with the potential for pregnancy in cows. This finding has interesting implications for human reproductive medicine.