A CRITICAL point during mammalian pregnancy is the implantation of the blastocyst when the embryo attaches to the wall of the uterus. The autonomously developing preimplantation embryo then becomes dependent on the maternal environment for its continued development. Little is known about the regulation of implantation, except that a complex interaction between peptide and steroid hormones synchronizes the preparation of the uterus for implantation with the development of the embryo. Whether the implantation event is under maternal or embryonic control is also unclear (reviewed in refs 1, 2). We have previously shown that a cytokine, leukaemia inhibitory factor (LIF), is expressed in the uterine endometrial glands specifically on the fourth day of pregnancy3. This burst of expression is under maternal control and always precedes implantation of the blastocyst. Here we report that transient expression of LIF in mice is essential for implantation. Females lacking a functional LIF gene are fertile, but their blastocysts fail to implant and do not develop. The blastocysts, however, are viable and, when transferred to wild-type pseudopregnant recipients, they can implant and develop to term.
Assisted hatching by zona drilling using acidic Tyrode's solution was performed during three randomized trials in 330 in-vitro fertilization patients. The trials were designed in order to study the overall effect of the procedure and whether characteristic patient [i.e. maternal age and basal levels of follicle stimulating hormone (FSH)] and embryonic features (i.e. zona pellucida thickness) are important for the decision to perform assisted hatching routinely. Couples (n = 137; Trial 1) in whom the female partner had normal basal FSH levels were randomized in a control group (without micromanipulation) and a zona drilling group (all embryos micromanipulated). The incidence of implantation (67/239; 28%) of zona-drilled embryos compared favourably with that of control embryos (49/229; 21%), but the difference was not significant. Retrospective analysis revealed that those embryos whose zonae were thicker than 15-mu-m were rescued. In order to test the validity of this finding, selective assisted hatching was performed on embryos with a poor prognosis in 163 other patients (Trial 2). The couples were randomized into a control group and a group in which embryos were selectively zona-drilled, based on zona thickness and other embryonic features. The rate of embryonic implantation in the selectively zona-drilled group was 25% (70/278), significantly (P < 0.05) higher than that of control embryos (51/285; 18%). Although it was demonstrated retrospectively and prospectively that assisted hatching by zona drilling is effective in embryos with thick zonae (greater-than-or-equal-to 15-mu-m), patients whose embryos have thin (< 13-mu-m) zonae may be jeopardized by the procedure. Selective assisted hatching appeared most effective in women over 38 and in those with elevated basal FSH levels.
Objective: To explore the possible similarities between the biochemical processes of embryo implantation and malignant invasion. Design: The expression of a basement membrane (BM) glycoprotein laminin, a matrix binding cell surface receptor protein beta-1-integrin, and a BM collagen degrading metalloproteinase type IV collagenase, was studied in cultured human in vitro fertilized embryos. Patients: Eighty healthy women suffering from tubal infertility were participating in the IVF program in the Department of Obstetrics and Gynecology in University Hospital of Oulu. Twenty oocytes and 110 pre-embryos that were not transferred for the fertilizations were used in this study. Main Outcome Measures: Fibronectin, laminin, beta-1-integrin, and type IV collagenase immunoreactive proteins were studied in embryos by immunoperoxidase staining, and type IV collagen degrading activity was measured from the culture media of the embryos. Results: Laminin and beta-1-integrin were expressed in the early human embryos before the time of implantation. Type IV collagen degrading activity and the 72 kd-type IV collagenase immunoreactive protein were expressed at the time of implantation. Laminin supported the expression of type IV collagenase. Conclusions: The expression of laminin, beta-1-integrin, and type IV collagenase in vitro are temporally in good correlation with the time of the implantation in vivo. Laminin and beta-1-integrin can relate to the attachment of the embryos to the uterine BM and type IV collagenase to the degradation of the BM collagen during the implantation. Laminin can augment the process locally.
Pre-implantation embryos were recovered from control, diabetic and insulin-treated diabetic rats on day 5 of pregnancy. Compared to control animals, diabetic rats had a 20 % reduction in the number of embryos per rat and blastocysts recovered from diabetic rats showed a 19 % decrease in total cell number. The cellular decrease observed in blastocysts was mainly at the expense of the inner cell mass. Insulin replacement therapy was started on day 1 of pregnancy and normalized the glycaemia of diabetic rats but failed to raise the number of embryos per rat toward the control value. Insulin treatment, however, fully restored the normal cell number in both the inner cell mass and trophectoderm of blastocysts. The dead cell index, which was significantly elevated in the inner cell mass of blastocysts from diabetic rats, also returned to the control value following insulin treatment. Our data suggest that diabetes-induced impairment of pre-implantation development can be partly prevented by insulin treatment started shortly after conception.
Objective: To gain insight into the peri-implantation period in the human and to answer the question whether timing of nidation is dependent on the stage of embryonic development, endometrial maturation, or a possible dialogue between the two. Design: Seventy-five women underwent embryo transfer (ET) throughout 93 cycles. Thirty-three ETs resulted in viable pregnancies and deliveries. These pregnancy cycles were used for embryonic signal detection. Embryos of identical age were transferred onto hormonally and histologically defined endometria of different maturational stages (days 15 to 19). Human chorionic gonadotropin (hCG) was measured by a hypersensitive chemiluminescence assay in maternal serum every 1 to 5 days to detect the first embryonic signal. Results: Individual linear regressions of hCG versus embryonic age and endometrial maturation were performed on 33 viable pregnancy cycles (r2 = 90.5% to 99.9%, P < 0.02 to 0.002). First signal detection was restricted to an embryonic age of 7.1 +/- 0.28 (mean +/- SD) days (range 6.6 to 7.4) irrespective of endometrial maturation. The pattern of hCG detection was triphasic, described by a sigmoidal curve with the maximal slope corresponding to an hCG doubling time of 15.9 hours. Embryo transfers on cycle day 19 had a steeper slope of hCG detection than days 15 and 16 (P < 0.05). Conclusions: First embryonic signal detection (presumed window of implantation) extends between cycle days 20 and 24. Implantation is dependent on embryonic age and is independent of endometrial maturation within this window. The timing and sigmoidal pattern of hCG detection coincides with structural changes of the implantation bed. The steeper slope of late ETs may represent a compensatory mechanism for late maternal recognition of pregnancy for corpus luteum rescue.
To elucidate the effect of nutrient substrates on embryo development, in vitro fertilized bovine one-cell embryos were cultured in a medium similar to synthetic oviduct fluid (SOF) but without glucose and containing 3.3 mM lactate, 0.3 mM pyruvate and 3 mg/ml bovine serum albumin (BSA) at 3-degrees-C in 5% CO2 in air. Results indicated that addition of glucose was not only unnecessary, but it also had a deleterious effect on embryo development to the morula stage. Lactate supported embryo development up to the morula stage as well as pyruvate. Supplementation with 20 amino acids contained in basal medium Eagle's (BME) and minimum essential medium (MEM) improved development to the morula stage dramatically and increased the cell number compared with that of the controls. Addition of the vitamins from MEM to SOF had no beneficial effect. The SOF with amino acids did not increase the frequency of blastocysts 7 days after invitro fertilization but did increase the total number of cells compared with that of the controls. Frequency of blastocysts at Day 7 in SOF with amino acids was equivalent to that of co-culture although the total cell number was lower. These results demonstrate that a semi-chemically defined medium can successfully support the development of bovine embryos to the morula stage to a limited extent, but the medium lacks some nutrients or growth factors to fully support development through the blastocyst stage.
Objective: To compare pregnancy and implantation rates in tubal and uterine transfers during a hormonal replacement cycle in an oocyte donation program. Design: Prospective randomized. Patients: Forty-two consecutive patients who entered an oocyte donation program. Interventions: Twenty-two patients were assigned for uterine transfer and 20 for tubal embryo transfer (ET). Results: Twenty-three pregnancies were achieved, 12 (54.5%) after uterine transfers and 11 (57.9%) after tubal transfers. Implantation rates in both groups are not significantly different (17.4% uterine transfers versus 21.5% tubal ETs). Conclusions: Our results suggest that in hormonal replacement cycles (uniform endometrial stimulation) there is no advantage in transferring embryos to the fallopian tube. Furthermore, embryo quality and endometrial receptivity appear to be significantly more important than the time of entrance of an embryo to the uterine cavity in determining its chances of implantation.
To assess the efficacy of gonadotropin-releasing hormone agonists (GnRH-a) used in ovulation induction for in vitro fertilization and embryo transfer (IVF-ET) and gamete intrafallopian transfer (GIFT). Meta-analysis of 10 trials comparing treatment cycle outcomes after GnRH-a (n = 914) with other ovulation induction protocols (n = 722) and 7 trials comparing outcomes after short flare-up (n = 368) with longer suppression (n = 476) GnRH-a protocols. The outcome of primary interest was clinical pregnancy rate (PR) per treatment cycle commenced. Data describing the amount of gonadotropin used, cycle cancellation rate, clinical pregnancy per ET, and multiple pregnancy and abortion rates were also analyzed. Clinical PR per cycle commenced was significantly improved after GnRH-a use for IVF (common odds ratio [OR] 1.80, 95% confidence interval [CI] 1.33 to 2.44) and GIFT (common OR 2.37, 95% CI 1.24 to 4.51). Clinical PR per embryo transfer was also significantly improved with GnRH-a use (common OR 1.40, 95% CI 1.01 to 1.95). Cycle cancellation was decreased (common OR 0.33, 95% CI 0.25 to 0.44), whereas spontaneous abortion rate was similar with and without GnRH-a use. Cycle cancellation and PRs after short flare-up and longer suppression protocols were similar between groups. This meta-analysis supports the routine use of GnRH-a for IVF and GIFT. Further research is needed, however, to assess the potential for increased rates of multiple pregnancy and ovarian hyperstimulation syndrome, which may be associated with this treatment.
Objective: To determine the possibility of obtaining good pregnancy rates (PRs) after freezing and thawing cocultured blastocysts. Design: Human blastocysts were frozen first according to a protocol available from literature. Two other protocols including the addition of glycerol were designed to improve the results. Setting: All the patients were under clinical management at the Institut Rhonalpin pour l'Etude de la Reproduction Humaine in Lyons, France. Patients: Patients involved in the in vitro fertilization program have had their supernumerary embryos frozen according to the three protocols presented here. Main Outcome Measures: Embryo recovery after freezing and thawing. Clinical and ongoing pregnancies after embryo transfer (ET). Results: A protocol including sucrose addition and reduction of steps in the preparation of the blastocysts for freezing gave us a 21% PR per transfer (15 ongoing) of 101 transfers (106 thawings). Conclusions: Freezing of cocultured human blastocysts allow good PRs. This can represent an alternative for repeated failures of ETs at early stages.