1 Fukuda Ladies Clinic, 309 Kariya, Ako, Hyogo 6780239, Japan and 2 Laboratory of Reproductive Biology, University Hospital of Copenhagen, Copenhagen, Denmark
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Abstract |
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Key words: anovulation in an ovary/corpus luteum/dominant follicle/pregnancy/two menstrual cycles
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Introduction |
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In order to study intra-ovarian factors affecting follicular and oocyte health we extended our previous studies and monitored three consecutive cycles. During all three cycles, the ovary from which follicular development, ovulation and corpus luteum formation took place was monitored by ultrasound. During the third cycle in-vitro fertilization (IVF) treatment was performed. The results from the IVF treatment were evaluated in relation to the position of follicular development, ovulation and corpus luteum formation during the previous two cycles.
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Materials and methods |
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The treatment cycles were grouped into ovulation group (O) or anovulation group (A), according to whether ovulation or anovulation (no ovulation) was seen in the previous cycle in the same ovary as that with the dominant follicle during the treatment cycle. In group A ovulation was seen in the opposite ovary. Groups O and A were each further subdivided into two groups according to whether ovulation (O-) or anovulation (A-) was seen in the same ovary in the previous second cycle: O-O and A-O; O-A and A-A (previous second cycle-previous first cycle). Based on the IVF treatment of the third cycle, oocyte retrieval rate/total number of follicles, fertilization rate, cleavage rate (cleaved embryo/fertilized embryo), rate of pre-embryo formation/total number of follicles, pregnancy rate/cycle and implantation rate (clinical pregnancies/pre-embryo replaced) were assessed in each group. Clinical pregnancy was confirmed with gestational sac by transvaginal ultrasound. Only singleton pregnancies were observed in the present study except one monozygotic twin. Part of the material from the present study has been used in previous studies (Fukuda et al., 1995, 1996
, 1998
).
Natural IVF cycles
Follicular development of 48 patients with a history of regular menses (29.4 ± 3.1 days) was monitored daily by transvaginal ultrasound (SSA-250A Toshiba scanner with a 5.0 MHz convex vaginal probe or Sonovista CS or EX Mochida scanner with a 5.0, 6.0 or 7.5 MHz mechanical sector vaginal probe) from the time when the follicle measured 14 mm in diameter until oocyte retrieval. During the luteal phase (i.e. from day 5 of ovulation onwards) the site of corpus luteum was confirmed. Ovulation was predicted by the urinary luteinizing hormone (LH) surge (L-check: Nipro, Osaka or Gold Sign LH: Morinaga, Tokyo, Japan). Cycles with more than two preovulatory follicles were excluded from the natural cycles. All procedures were performed as described previously (Foulot et al., 1989; Fukuda and Fukuda, 1997b
). In brief, human chorionic gonadotrophin (HCG) was given when the dominant follicle measured more than 18 mm in diameter and the oocyte was retrieved 3435 h after HCG injection using transvaginal ultrasound guided follicle puncture and the follicle was flushed up to six times.
Clomiphene citrate IVF cycles
Forty-four patients received 50150 mg/day of CC (Serophene®; Serono, Tokyo, Japan) from day 5 of the cycle for 5 days. The usual dose was 50 mg/day for 5 days and was only increased if ovarian response proved unsatisfactory in an earlier treatment cycle. The indications for administration of CC were as follows: (i) ovulation disorder, i.e. oligo-ovulation, anovulatory cycle; (ii) patients showing an endogenous LH surge with a dominant follicle of <17 mm in diameter during a natural IVF cycle. In CC cycles human chorionic gonadotrophin (HCG) was given when the leading follicle measured >20 mm in diameter. Preovulatory follicles measuring 14 mm or more were also aspirated and flushed up to six times. Bilateral ovulation cycles were excluded from the third cycles for IVF treatment in the present study.
Statistical evaluation was performed using 2 test or Fisher's exact test. Differences were considered significant at P < 0.05. Results are presented as mean ±SD.
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Results |
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IVF outcome in clomiphene citrate cycles
IVF outcomes in CC cycles are summarized in Table II. The oocyte retrieval rate/total number of follicles (88%) and fertilization rate (88%) in group A were significantly higher than those of group O (76 and 68% respectively). However, the cleavage rates were similar and high in both groups A (97%) and O (91%). The rate of pre-embryo formation/total number of follicles in group A (75%) was significantly (P < 0.0005) higher than that of group O (47%). As a result, the pregnancy rate/cycle in group A (28%) was significantly (P < 0.05) higher than that of group O (10%).
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IVF outcome in both natural cycles and clomiphene citrate cycles
IVF outcomes in natural cycles and CC cycles combined are summarized in Table III. The oocyte retrieval rate/total number of follicles (90%), the fertilization rate (87%), the cleavage rate (93%) and the rate of pre-embryo formation/total number of follicles (73%) in group A were significantly higher than those of group O (74, 68, 77 and 39% respectively). As a result the pregnancy rate/cycle in group A (20%) was also significantly (P < 0.005) higher than that of group O (7%).
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Discussion |
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The favourable health of oocytes from ovaries which were ovulatory inactive during the previous two cycles is obtained as a collective result of better rates of oocyte retrieval, fertilization, cleavage and pre-embryo development. Similar results are obtained in natural menstrual cycles and in CC stimulated cycles, and the effects are as a consequence clearly expressed when data from these two groups are combined.
If an oocyte experiences a local hostile environment caused by the development of a dominant follicle and/or the formation of a corpus luteum in an ovary, a permanent negative impact may be imposed on the oocyte, whereas the somatic cells of the follicle may, in response to gonadotrophin stimulation, regenerate health and enable them to acquire dominance in the follicular phase of a later cycle. Therefore, the present study does not question the generally accepted notion of the dominant follicle being selected during the late luteal phase and the early follicular phase of the menstrual cycle, but emphasizes that the oocyte of the selected follicle may not be the healthiest one present in the cohort of responsive follicles, and proposes that follicular and oocyte health may not inevitably be linked, i.e. the follicular cells may be healthy, whereas the oocyte of that follicle may not.
The implantation rates in A-A and A-O showing anovulation in an ovary two cycles previously seem to be twice as high as those of O-A and O-O. This may indicate that anovulation in the previous second cycle not only improves oocyte health but also causes a better quality corpus luteum secreting steroid hormones appropriate for implantation and optimal uterine receptivity.
The results of the present study together with our previous studies (Fukuda et al., 1996, 1998
) may reflect that progesterone or the corpus luteum exerts a local paracrine antifolliculogenic effects on follicles before they reach gonadotrophin-dependent follicular growth. Progesterone has been shown to have such an antifolliculogenic effect (Moore and Greenwald, 1974
; Mizuno et al., 1976
; Akahori, 1978
; Fukuda et al., 1980
; Schreiber et al., 1980
, 1981
, 1982
; Tyler et al., 1980
). Progesterone may inhibit follicle-stimulating hormone (FSH)-stimulated granulosa oestrogen production (Schreiber et al., 1980
, 1981
, 1982
) through a progesterone-binding protein with receptor like features located on the surface of granulosa cells (Peluso and Pappalardo, 1998
).
A number of studies are in agreement with the present study: Lass et al. (1997) showed poor ovulation responses in women with a single ovary and a lower IVF pregnancy rate was observed in women with only one ovary (17%) compared to those with two ovaries (28%) (Khalifa et al., 1992). The decreased conception rate of women with one ovary may reflect that continuous ovulations produce suboptimal oocytes.
Sackoff et al. (1994) indicated that women who conceived within the first ovulation or even the second ovulation after termination of taking oral contraceptives had a lower risk of chromosomally normal spontaneous abortions, supporting the observations of the present study. Moreover, a previous work showed that down-regulation with luteinizing hormone-releasing hormone agonists for 34 months improves implantation rates (Edwards, 1996). Reports have also shown that induced anovulation using oral contraceptives prior to ovarian stimulation with gonadotrophins improves IVF and pregnancy outcome (Fisch et al., 1996
; Damario et al., 1997
). These studies are also in agreement with the present data and our previous studies (Fukuda et al., 1996
, 1998
) showing that a previous ovulatory quiescent ovary favours pregnancy. Therefore, anovulation using oral contraceptives prior to CCIVF treatment may offer a milder form of ovarian stimulation as proposed by Edwards et al. (1997).
Women in the general population without any known fertility problem who seek to achieve a pregnancy experience a conception rate of around 2530% per cycle. This is surprisingly low and ranks humans as poor breeders compared to other species. While a number of factors undoubtedly contribute to the low fertility of humans, the present study demonstrates a mechanism which may reduce the natural occurring fertility of humans. It will be of interest to evaluate whether other single ovulatory species like the large domestic animals show a similar pattern affecting the health of the oocyte contained in the dominant follicle.
In conclusion, the health of the oocyte from the dominant follicle seems to be affected by local ovarian conditions earlier, up to two menstrual cycles, than previously shown. The presence of a corpus luteum and/or a dominant follicle is likely to exert unfavourable local effects on the oocyte contained in the follicle which may subsequently be selected to ovulate one or two cycles later. Anovulations in an ovary (an ovulatory quiescent ovary) during two menstrual cycles provide improved conditions for the development of a healthier oocyte with an increased pregnancy potential. This study strongly proposes clinical application of anovulation using oral contraceptives prior to IVF treatment.
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Notes |
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References |
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Submitted on June 12, 1998; accepted on October 14, 1998.