Tentative extrapolation of animal data to human implantation

The effect of estradiol depletion during the luteal phase on endometrial development

OBJECTIVE

To examine whether luteal E2 is obligatory for obtaining an adequately developed endometrium.

DESIGN

Survey of women with premature ovarian failure (POF) in a prospective, controlled, randomized study.

SETTING

In vitro fertilization unit in a tertiary care university medical center.

PATIENTS

Fourteen amenorrheic women with POF, candidates for oocyte donation, were divided into two distinct groups with seven women in each subgroup.

INTERVENTIONS

Endometrial priming with a fixed dose of oral micronized E2, 4 mg/d for 14 days, was similarly performed in the study and the control groups. Progesterone replacement during the luteal phase was also identical in the two groups and was accomplished by IM P in oil, 50 mg/d for another 14 days. Only the control group continued to have the same E2 regimen during the luteal phase.

MAIN OUTCOME MEASURES AND RESULTS

Follicular phase mean E2 levels as well as luteal phase mean P levels were similar in both groups. However, luteal E2 levels differed significantly between the study and the control groups (21 +/- 5 and 692 +/- 199 pg/mL, respectively; conversion factor to SI units, 3.671). Nevertheless, histologic evaluation of endometrial biopsies on days 21 and 26 were similar for both groups. Endometrial gland dating, using light microscopy in the study and the control groups, on day 21, was 19.1 +/- 0.8 and 18.4 +/- 0.5, respectively, and on day 26, 25.4 +/- 0.8 and 25.9 +/- 0.5, respectively. Dating of the stroma in the two biopsies was also similar in both groups. Moreover, transmission electron microscopy performed in two patients of the study group showed typical characteristics of a secretory endometrium.

CONCLUSIONS

Luteal E2 depletion in the human does not seem to adversely affect the morphological developmental capacity of the endometrium. Our results suggest that E2 secretion by the corpus luteum in the human does not appear to be obligatory for the development of a normal secretory endometrium. The actual receptivity of the endometrium after such preparation needs to be evaluated.

The endometrial biopsy as a predictive factor of pregnancy rate in women with unexplained infertility

To investigate whether or not there is any relation between endometrial morphology and subsequent pregnancy rate, 47 couples with unexplained infertility were followed up for 3 years after they had had an endometrial biopsy. Each woman had an LH-timed endometrial biopsy performed in the luteal phase of the cycle. The biopsy was dated chronologically according to the luteinizing hormone (LH) surge and histologically using morphometric criteria. None of the women received any form of treatment in the endometrial biopsy cycle. Of 47 women with unexplained infertility, 36 (76.6%) (Group I) had 'in phase' endometrial development and 11 (23.4%) (Group II) had retarded endometrium. Women with normal endometrial development had a higher pregnancy rate than women with retarded endometrial development (50% vs. 9%; P less than 0.02). The fecundability during treatment cycles was higher in Group I than in Group II (0.051 vs. 0.008; P less than 0.05). In women with 'in phase' endometrium, treatment increased the monthly probability of conception (0.051 vs. 0.006; P less than 0.001). A precisely timed endometrial biopsy should be considered as part of the investigations for women with unexplained reproductive failure, to help determine prognosis.

Uterine receptivity for blastocyst implantation

The receptivity for blastocyst implantation is controlled by progesterone and in some species by the synergistic action of progesterone and estrogen. The duration of the receptive phase, the so-called "window," is short in rodents (less than 24 hours) and may be three days in the primate. Once the uterus becomes receptive, it automatically becomes refractory at the end of the receptive phase. The uterus in the refractory phase can be toxic to the blastocyst in small laboratory animals. The endometrium of the receptive uterus may be characterized by the following parameters: (1) Formation of bulbous protrusions on the apical surface of the luminal epithelium; (2) Secretion of the stage-specific glycoproteins by the luminal epithelium; (3) Readiness of stromal cells to decidualize when appropriate stimulation is applied; and (4) Reorganization and changes of stromal extracellular matrix components so that stromal cells are conditioned for decidualization, and after decidualization the appearance of basement membrane components in the matrix.

Effect of short-duration progesterone treatment on decidual prolactin production by cultures of proliferative human endometrium

The effect of short-term progesterone (P) treatment in vitro on decidual prolactin (dPRL) production by human endometrium was investigated. Cultures prepared from proliferative endometrium received medium containing P for 3 hours, 1 day, or 3 days. The culture medium was then changed daily for 7 to 14 days, and the amounts of dPRL in the spent medium were measured by radioimmunoassay. The results of these experiments indicated that even a short exposure to elevated concentrations of P is adequate to stimulate dPRL production and that the resulting pattern of dPRL production is determined by the duration of the P treatment.

Endometrial morphology in stimulated in vitro fertilization cycles and after steroid replacement therapy in cases of primary ovarian failure

Endometrial morphology and ultrastructure are studied in 17 spontaneous, 23 stimulated, and 18 artificial cycles in cases of primary ovarian failure. Normal light-microscopic aspect was found, but impaired development of nucleolar channel system and stronger intercellular junction have been observed by electron-microscopic studies in stimulated cycles with relative excess of luteal estrogen. Normal glandular maturation can be obtained in patients with premature menopause, given adequate steroid replacement, but an abnormally dense fibrocytic aspect of the stroma is characteristic of the first treatment cycles.

Differences in the luteal phases after failed or successful in vitro fertilization and embryo replacement

Luteal phases after in vitro fertilization (IVF) and embryo replacement have been studied in 241 cycles. A positive correlation was observed between the follicular estradiol (E2) peak and the progesterone (P) level on day 3 of the luteal phase, but no correlation was found between the E2-peak value and the luteal-phase duration or midluteal P concentration. When the trials were classified in relation to their outcome (i.e., clinical pregnancies, chemical pregnancies, or failures), the mean P level on day 3 of the luteal phase was significantly higher in clinical pregnancies than in chemical pregnancies and in failures. Mean E2 levels on day 3 were not significantly different among the three groups. Values of the E2/P ratio were significantly higher in chemical pregnancies than in the other groups. No significant differences were observed among the three groups on day 8. When comparing trials ending in failure to those leading to clinical pregnancy for the same patients, pregnancies were obtained in cycles in which early luteal P was higher and the early luteal E2/P ratio was lower than in failures cycles. These data suggest that high P levels and a low E2/P ratio in the early luteal phase might have a favorable influence on the implantation process in human IVF.