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1.
PURPOSE: To assess the impact of assisted hatching on in vitro fertilization (IVF) outcome in women age 40 and older. METHODS: A retrospective analysis was performed to compare 28 cycles of IVF without assisted hatching to 38 cycles of IVF with assisted hatching. All patients in both groups were age 40 or older and the mean age was similar. RESULTS: The delivery rate per oocyte retrieval was significantly higher in the assisted hatching group (18/38; 48%) compared to the nonhatched controls (3/28; 11%, P = 0.0003). The implantation rate of hatched embryos (40/175; 22%) was clearly enhanced, compared to the nonhatched embryos (7/126; 6%, P < 0.001). The fertilization rate, number of oocytes and the number of embryos per patient were comparable in the two groups. CONCLUSIONS: Assisted hatching dramatically improves embryonic implantation and term pregnancy rates in women age 40 and older undergoing IVF.  相似文献   

2.
OBJECTIVE: To compare the results of pelvic reconstructive surgery with cumulative success rates of IVF for couples with tubal factor infertility. DATA RESOURCES: Outcomes of pelvic surgery were obtained from a review of articles from the literature identified by directed Medline searches. Cumulative pregnancy rates of 771 couples with tubal factor infertility treated at the Cornell IVF program between December 1989 and December 1992 were calculated by life-table analysis. RESULTS: Overall delivery rate per transfer for patients with tubal factor was 28.9% (303 deliveries per 1,048 transfers) and did not appear to be affected significantly by the presence of a secondary diagnosis. A significant decline in pregnancy rates was observed with advancing age: age < 30 years, 48.4%; 30 to 34 years, 44%; 35 to 38 years, 28%; 39 to 40 years, 20%; 41 to 42 years, 9%; and > 42 years, 4.3%. Cumulative pregnancy rates for cycles 1 to 4 were 32%, 59%, 70%, and 77%, respectively, in patients with only tubal factor, and 28%, 55%, 62%, and 75% in patients with tubal combined with other associated infertility factors. CONCLUSIONS: Our experience suggest that > 70% of women with tubal factor infertility will have a live birth within four cycles of treatment with IVF. These results compare favorably with the best outcomes after tubal reconstructive surgery. In older women, because of the rapid decline of fertility potential with advancing age, efforts should be directed toward the treatment method that provides the highest likelihood of success within the shortest time interval.  相似文献   

3.
OBJECTIVE: To evaluate the results of IVF in women > or = 40 years of age using their own oocytes. DESIGN: Retrospective study. SETTING: Wolfson and Royal Masonic in vitro fertilization units, London, United Kingdom. PATIENT(S): A total of 1,087 IVF cycles were started in women > or = 40 years of age. INTERVENTION(S): Medical records of patient outcomes were reviewed. MAIN OUTCOME MEASURE(S): Clinical pregnancy, miscarriage, and delivery rates. RESULT(S): Of the 1,087 cycles started in 471 women > or = 40 years of age, 842 reached oocyte retrieval (77.5%) and 702 had embryos transferred (64.6%). The pregnancy rate (PR) was significantly lower in women > or = 40 years of age than in a control group of women <40 years of age (11.3% versus 28.2%). It decreased sharply in women >42 years of age, and no women >45 years of age had a child. Women > or = 40 years of age were more likely to miscarry (27% versus 12.7%). When only one embryo was available for transfer, the PR was 3.3%. When >2 embryos were available for transfer, the PR was similar whether 2 or 3 embryos were replaced. No triplet pregnancy occurred. Women > or = 40 years of age achieved a cumulative PR of 30% after three cycles with a cumulative "take home baby" rate of 21%. CONCLUSION(S): In vitro fertilization is a reasonable treatment for women <45 years of age using their own gametes. Those with a "good response" in their first attempt may be encouraged to complete three cycles with an acceptable chance of conception.  相似文献   

4.
OBJECTIVE: To access the effect of augmenting IVF with assisted hatching in the treatment of poor-prognosis patients. DESIGN: Thirty-three poor-prognosis IVF patients were treated with assisted hatching and were compared with 43 control subjects without assisted hatching. SETTING: Center for Reproductive Medicine, Swedish Medical Center, Englewood, Colorado. PARTICIPANTS: Seventy-six women undergoing IVF with a poor prognosis for pregnancy. Poor prognosis was defined as Elevated day 3 FSH level; age > or = 39 years; and multiple prior IVF failures. MAIN OUTCOME MEASURES: Pregnancy and implantation rates per embryo. RESULTS: The incidence of ongoing pregnancy in the assisted hatching group was 64% compared with 19% in the control group. Implantation rate per embryo transferred was 33% in the assisted hatching group versus 6.5% in the control group. CONCLUSIONS: These results demonstrate that assisted hatching, when applied to poor-prognosis patients, improves embryonic implantation and pregnancy rates.  相似文献   

5.
OBJECTIVE: To analyze data from a large multicenter study to determine whether pregnancy and delivery rates decrease with repeated IVF-ET cycles. DESIGN: Multicenter retrospective study. SETTING: Participating centers from the Society of Assisted Reproductive Technology. PATIENT(S): Fifty-four centers contributed 4,043 cycles of oocyte retrieval for uterine transfer. INTERVENTION(S): Oocyte retrieval for uterine transfer. MAIN OUTCOME MEASURE(S): Pregnancy and delivery rates, analyzed according to age, program success rate, and whether the program was doing assisted hatching. RESULT(S): Pregnancy and delivery rates for cycles 1, 2, 3, 4, and >4 were 33.7% and 27.0%, 33.9% and 27.4%, 28.9% and 23.4%. 25.9% and 16.1%, and 21.0% and 15.4%, respectively. The pregnancy rate decreased significantly for >4 cycle; delivery rate decreased significantly for cycles 4 and >4. Assisted hatching was strongly related to better odds of pregnancy (OR, 1.50) and delivery (OR, 1.44) in women under age 40, and for pregnancy (1.64) in women age 40-42 years. CONCLUSION(S): Success rates do not decrease markedly with repeated IVF attempts, and the decrease did not change with program success rate, suggesting the IVF population is not markedly heterogeneous. Uncontrolled studies of new treatments for cycle repeaters cannot assume that success rate is poor without a treatment change.  相似文献   

6.
Due to a paucity of donated eggs, we have excluded, until recently, couples with severe male factor infertility from our egg donation programme, except for those who accepted insemination with donor spermatozoa. The purpose of this study was to assess the feasibility of a shared in-vitro fertilization (IVF)-embryo transfer treatment whenever the recipients have severe oligoasthenoteratozoospermia (OTA) and need intracytoplasmic sperm injection (ICSI) for egg fertilization. The results from 163 consecutive couples with ovarian failure who underwent 273 cycles of IVF with donated eggs and augmented with ICSI were analysed. The rate of diploid fertilization was 54.7%; in 92.3% of the cycles, at least one embryo was available for transfer. Forty-seven clinical pregnancies were achieved, representing 18.6% conceptions per transfer. The highest pregnancy rate was achieved in menopausal patients aged 40-45 years (26.2% per cycle) and the lowest in patients >45 years old (10.8% per cycle, P = 0.03). Overall, 28.8% of the couples achieved a clinical pregnancy. A total of 196 treatment cycles resulted in 46 clinical pregnancies (23.5%) among the donors. No statistical differences were found in pregnancy rate achieved by the donors when compared with the recipients. We conclude that ICSI with egg donation is a reliable treatment in patients with ovarian failure and severe OTA.  相似文献   

7.
OBJECTIVE: To compare the cumulative probability of pregnancy after multiple IVF cycles by age and cause of infertility. DESIGN: A prospective study was done in which patients were followed from the time they registered for their first IVF cycle until they achieved a clinical pregnancy, withdrew from treatment, or study was terminated. PATIENTS, SETTING, TREATMENTS: Infertile women undergoing IVF-ET at the Cooper Institute for In Vitro Fertilization were enrolled in this study if the luteal phase leuprolide acetate (LA) and hMG controlled ovarian hyperstimulation (COH) regimen was used. MAIN OUTCOME MEASURES: Clinical pregnancy, as determined by a positive beta-hCG level and ultrasonographic confirmation of a gestational sac, and delivery rates based on number of women with live births were compared by infertility factor and age. RESULTS: The 3-month cumulative probability of pregnancy based on life table analysis was 33% in women with tubal factor who were < or = 35 years of age, 25% in women with tubal factor who were > 35 years of age, 30% for women with multiple factors who were < or = 35 years of age, and 14% for women with multiple factors who were > 35 years of age. The rate for the older women with multiple factors was significantly lower than that for the other groups. The delivery rates were lower for the women with multiple factors than for women under 35 with tubal factor only. CONCLUSIONS: There is a significant effect of age and infertility factor on pregnancy and delivery rates. Physicians should consider these factors in evaluating their patients' prospects for success in IVF-ET.  相似文献   

8.
To evaluate the efficacy of gamete intra-Fallopian transfer (GIFT) the Kaplan-Meier life table method was used to analyse a patient cohort treated with GIFT between 1991 and 1994. In a tertiary referral centre for reproductive medicine, 1628 women with a median age of 33 years and various causes of infertility were included to calculate cumulative pregnancy and live birth rates. Age and cause of infertility were main factor variables and the study was based on a total of 2941 consecutive GIFT cycles, leading to a first clinical pregnancy, and 3052 cycles, leading to a first live birth. The cumulative pregnancy and live birth rates were 49.6 and 38.8% respectively, after three initiated cycles and 64.1 and 52.0% respectively, after five initiated cycles. The multiple pregnancy rate was 22.6%. The implantation rate of 13.1% after GIFT demonstrates that the developing embryo benefits from a period of exposure within the environment of the Fallopian tube. The present results indicate that approximately 50% of couples will have at least one live baby after five initiated GIFT cycles. Advancing age was a major negative prognostic factor for the cumulative live birth rate because of higher cancellation rates, lower implantation rates and higher pregnancy failure rates.  相似文献   

9.
This study examines the relationship between the first cycle of in-vitro fertilization (IVF) and subsequent cycles. The results of all IVF cycles conducted at The Hammersmith Hospital or The Royal Masonic Hospital between 1988 and 1995 were studied including those cycles where egg recovery was abandoned due to poor ovarian response. All patients underwent a standardized treatment protocol. Of those women who achieved a clinical pregnancy during their first IVF attempt, 33% achieved a pregnancy during their second cycle, statistically significantly different from the 24% of patients conceiving during a second cycle who had failed to conceive during their first. 36% of those who achieved a biochemical pregnancy in their first cycle became pregnant in their second. Age was an important factor in the success of IVF treatment, with pregnancy rates of 48% in the 20-25 year age group falling to 8% in those aged > or =41 years. Cumulative pregnancy rates were 26% after one cycle, increasing to 43% after two cycles and reached 80% after seven cycles. A previous pregnancy significantly improved a couple's probability of conception in a later IVF cycle. Overall pregnancy rates per cycle were constant for the first three attempts. Cumulative pregnancy rates continued to rise to 72% after six cycles. Thus the more cycles a couple undergo (up to six) the greater their chance of a pregnancy.  相似文献   

10.
Data were analysed from 710 couples who had been assessed to determine the effectiveness and the drawbacks of three different methods of insemination using frozen donor semen. Intracervical insemination (ICI) was the first method used when the women had no tubal disorder: 255 pregnancies were achieved in a total of 2558 cycles (10%). Intrauterine insemination (IUI) associated with ovarian stimulation resulted in 152 pregnancies over 966 cycles (16%). In-vitro fertilization (IVF) was proposed after approximately 12 insemination failures using either of the other methods or when the initial gynaecological examination had revealed abnormalities such as tubal occlusions; 48 pregnancies were obtained in 262 cycles (18.3%). The pregnancy rate using ICI was significantly higher when two inseminations were performed per cycle, compared with one insemination per cycle (12.3 versus 7%, P < 0.001). The number of motile spermatozoa per straw was correlated with the pregnancy rate when using ICI, rising from 9% with < 4 x 10(6) motile spermatozoa to 13.8% with 4-8 x 10(6) and 17.2% with > 8 x 10(6). No relationship was found between the number of motile spermatozoa and the pregnancy rate using IUI and IVF. The incidence of primary ovulatory disorder was higher among women whose husbands were oligozoospermic than among those whose husbands were azoospermic (19 versus 9%, P < 0.01), but ovarian stimulation improved the fecundity of subfertile women. The outcome of pregnancies was also analysed for the three methods. From these data, strategic plans have been proposed to maximize the pregnancy rate for women undergoing therapeutic donor insemination with frozen semen.  相似文献   

11.
All assisted conception techniques are associated with an increase in the multiple pregnancy rate. Iatrogenic multiple births are increasing as the use of these technologies expands. The cornerstone of safe ovulation induction is careful ultrasound monitoring, with cancellation of cycles if excessive ovulation is expected. In in vitro fertilization (IVF) cycles, the main determinant of multiple pregnancy risk is the number of embryos replaced. The current move in IVF clinics is to reduce the risk of multiple pregnancy by reducing the number of embryos transferred. We would suggest a maximum of two embryos transferred to women under, for example, 39 years of age. Women of 39 years or over have a reduced chance of embryo implantation; they should be allowed the transfer of up to three embryos (the UK legal maximum).  相似文献   

12.
The objective of this study was to compare prospectively pregnancy outcome as it is related to ultrasonic endometrial echo pattern in women exposed to diethylstilboestrol (DES) in utero by their mother's consumption with women not exposed to DES, all of whom were undergoing in-vitro fertilization (IVF). Pregnancy outcome relative to endometrial thickness and pattern was evaluated in 540 cycles of IVF including DES (n = 50) and non-DES-exposed (n = 490) women. Endometrial patterns were designated as p1 = solid; p2 = ring; and p3 = intermediate. DES patients exhibited p1 more often than the majority of the non-DES-exposed group. There was no significant difference in endometrial thickness among the cycles where p1 was noted when comparing the DES (10.3 mm) with the non-DES-exposed (10.7 mm) groups. Notably, within the group exhibiting p1, no pregnancies occurred in the 18 cycles of DES-exposed women compared with a 39.2% clinical pregnancy and 36.5% delivery rate in the non-DES-exposed controls (P < 0.0001 and P = 0.008 respectively). Pregnancy rates were not significantly different in the cycles where the other endometrial patterns were found when comparing the two groups. The impact of uterine shape on pregnancy outcome was also investigated. A T-shaped uterine configuration was noted in 11 out of 18 (61.1%) cycles of DES-exposed women with pattern p1 compared with nine out of 23 (39.1%) with pattern p2. Of cycles where a T-shaped uterus was demonstrated, none out of 11 (0%) with pattern p1 compared with four out of nine (44.4%) with pattern p2 resulted in pregnancy (P = 0.026). These data suggest that endometrial pattern is one of the most significant variables for pregnancy outcome in DES-exposed women undergoing IVF.  相似文献   

13.
There are numerous studies concerning pregnancy rates in oocyte donation, yet only a handful report the obstetric outcome in such pregnancies. The purpose of this study was to assess factors that influence pregnancy rates, to determine the incidence of complications, and to evaluate obstetric outcome in pregnancies resulting from oocyte donation. This study included 423 oocyte recipients who underwent 1001 oocyte donation cycles at the Oocyte Donation Programme, In-Vitro Fertilization (IVF)-Embryo Transfer Unit, Herzlia Medical Center, Israel. Donors were all healthy women < 34 years old who underwent IVF themselves. In 873 cycles, fertilization occurred and embryo transfer was performed, resulting in 194 clinical pregnancies. Pregnancy rates (PR) significantly declined with the increase in number of previous attempts, and with increasing age of recipient (36.8%/embryo transfer in patients < or = 30 compared to 17.8% in patients > 40 years old). A significant increment in PR was noted with the increasing number of embryos transferred. The overall PR was 22.2%/embryo transfer. However, in young amenorrhoeic patients with normal karyotypes undergoing their first cycle, PR was 52.2%; the 'take home baby' rate was 38.3% per patient undergoing embryo transfer and 17.8% per embryo transfer cycle. A significant increase in the incidence of pregnancy-induced hypertension and a higher proportion of abortions were noted in older patients. A significantly higher incidence of prematurity and low birthweight was observed in multiple pregnancies.  相似文献   

14.
A matched follow-up study design was used to test the hypothesis that pregnancy rates following assisted reproduction procedures do not differ between women with or without intramural or sub-serosal uterine leiomyomas. Women undergoing their first in-vitro fertilization (IVF)-embryo transfer or zygote intra-Fallopian transfer (ZIFT) cycle between January 1993 and June 1995 were included. Cases (women with leiomyomas) were matched 1:1 with the next consecutive control (women without leiomyomas) according to age, number of embryos transferred, embryo grade, and the route of embryo transfer (uterine or Fallopian). Assisted reproduction cycles were performed in an identical manner, independent of the presence or absence of uterine leiomyomas. The main outcomes measured were clinical pregnancy and delivery rates. A total of 182 cycles was evaluated. Of the 91 assisted reproduction cycles performed in the leiomyoma group, there were 34 clinical pregnancies (37%) and 30 deliveries (33%). Of the 91 assisted reproduction cycles in the control group, there were 48 clinical pregnancies (53%) and 44 deliveries (48%). The Mantel-Haenszel estimate of relative risk indicated that the presence of a uterine leiomyoma significantly reduced the chance for a clinical pregnancy or delivery. These findings suggest that leiomyomas are associated with a reduction in the efficacy of assisted reproduction cycles.  相似文献   

15.
OBJECTIVE: To evaluate whether endometrial receptivity is compromised in patients with premature ovarian failure (POF) due to Turner's syndrome who undergo oocyte donation. DESIGN: Retrospective analysis. SETTING: In vitro fertilization-ET units, anonymous oocyte donation program. PATIENTS: The study included 53 patients with POF who underwent oocyte donation. These included 7 patients with Turner's syndrome (45,X) who underwent 22 ET cycles, 15 women with Turner variants (mosaics, deletions, or isochromosomes) who underwent 36 ET cycles, and 31 other patients with POF and a normal karyotype who underwent 69 oocyte donation cycles. INTERVENTION: All patients on standby for donation were treated with E2 valerate 6 mg/d until oocytes became available; then P 100 mg/d was added. Oocyte donors were healthy women < 34 years who underwent IVF themselves. MAIN OUTCOME MEASURES: Clinical pregnancy rates (PRs), biochemical pregnancies, early abortions, and delivery rates were evaluated. RESULTS: Turner's syndrome patients had a significantly higher rate of biochemical pregnancies (22.7% versus 4.3%), a lower clinical PR (22.7% versus 33.3%), a significantly higher rate of early abortions (60% versus 8.7%), and a significantly lower rate of deliveries per pregnancy (20.0% versus 73.1%) compared with non-Turner patients. CONCLUSIONS: Patients with a complete or partial deficiency of an X chromosome have reduced PRs and an increase in early implantation failure after oocyte donation. This may indicate an inherent endometrial abnormality, possibly associated with a deficiency of X-linked genes regulating endometrial receptivity.  相似文献   

16.
BACKGROUND: The effectiveness of in-vitro fertilisation (IVF) treatment depends both on the overall success rate in the treating clinic and on the characteristics of the couple seeking treatment. Since 1991, the Human Fertilisation and Embryology Authority (HFEA) has been collecting information on all IVF cycles carried out in the UK. This database has been analysed to identify the factors that affect the outcome of treatment. METHODS: All IVF treatment cycles and outcomes registered between August, 1991, and April, 1994, were identified (52507). Cycles that involved gamete or embryo donation, frozen embryo transfer, or micromanipulation and unstimulated cycles were excluded. Thus, 36961 cycles (70% of those registered) were included in the analysis. The main outcome measure was liverbirth rate per cycle started. The relation between age and outcome was investigated by fitting of different fractional polynomials of age with logistic regression models. All other factors were analysed by logistic regression with age included in the model. FINDINGS: The overall livebirth rate per cycle of treatment was 13.9%. The highest livebirth rates were in the age-group 25-30 years; younger women had lower rates and there was a sharp decline in older women. At all ages over 30, use of donor eggs was associated with a significantly higher livebirth rate than use of the woman's own eggs, but there was also a downward trend in success rate with age (p = 0.04). After adjustment for age, there was a significant decrease in livebirth rate with increasing duration of infertility from 1 to 12 years (p < 0.001). The medical indication for treatment had no significant effect on the outcome. Previous pregnancy and livebirth significantly increased treatment success. The possibility of success decreased with each IVF treatment cycle. INTERPRETATION: We were able to identify by logistic regression the factors that significantly affect the outcome of IVF treatment, and to measure the magnitude of that effect. These factors should be taken into account in assessment of IVF results. After allowance for background clinic success rates, these factors can be used to predict outcome in individual cases.  相似文献   

17.
OBJECTIVE: To describe our experience with natural cycle IVF making clinical and endocrine comparisons with our standard stimulated cycle IVF program. DESIGN: We attempted 75 natural IVF-ET cycles with hCG given to preempt the LH surge and compared these with 450 attempts at standard superovulation IVF-ET done in our unit during the same time period. PATIENTS: Natural cycle patients are normally ovulating women < age 38. Superovulation IVF-ET patients are all < 41 years old. Patients in both groups had partners with normal semen parameters and tubal factor infertility. MAIN OUTCOME MEASURES: Cancellation rates, pregnancy rates per egg retrieval, per ET procedure, and luteal phase E2:P ratios of the treatment cycles are compared. RESULTS: There were 35 of 75 (47%) natural cycle and 112 of 450 (25%) superovulation cycle cancellations. An egg was retrieved in only 24 of 40 (60%) natural cycles and 336 of 338 (99%) superovulation egg retrieval procedures. Pregnancy rates per ovum pick-up procedure were significantly higher: 65 of 338 (19%) in the superovulation versus 2 of 40 (5%) in the natural cycle groups. Pregnancy rates per ET were not significantly different between natural IVF-ET, 2 of 18 (11%) and superovulation IVF-ET, 65 of 298 (22%). The E2:P ratios 5 days after ET were similar in both groups at 18 +/- 4 after natural IVF-ET and 21 +/- 18 after superovulation IVF-ET. CONCLUSIONS: [1] Cancellation rates for natural cycle IVF are very high. [2] Midluteal E2:P ratios are the same in both groups. [3] Pregnancy rates per egg retrieval are significantly lower for natural versus superovulation IVF-ET. [4] In our experience, natural cycle IVF-ET is an inefficient therapy for tubal infertility compared with superovulation IVF-ET.  相似文献   

18.
The experience of transferring embryos produced through in-vitro fertilization (IVF) utilizing donated oocytes and spermatozoa is described. Recipients (n = 28; aged 38-59 years) received oral micronized oestradiol and i.m. progesterone and were synchronized to donors undergoing ovarian stimulation. Reasons for selecting therapy included advanced reproductive age (> 42 years; n = 21) or hypergonadotrophic hypogonadism (n = 7), combined with severe male factor infertility in 23 couples. Five women were single and without partners. Oocytes were fertilized by cryopreserved spermatozoa designated for use by the recipient. Up to five embryos were transferred transcervically. Supernumerary embryos were cryopreserved. A total of 36 aspirations produced 15.6 +/- 7.3 oocytes per retrieval. In 10/36 cycles (27.8%), embryos were available for cryopreservation. Using fresh embryos, the overall pregnancy rate was 38.9% (14/36), clinical pregnancy rate 33.3% (12/36), and ongoing/delivered pregnancy rate 30.6% (11/36). Three ongoing pregnancies were later established by transferring cryopreserved embryos. Adjusting for these events, the per aspiration overall pregnancy rate per retrieval was 47.2%, clinical pregnancy rate 41.7%, and ongoing/delivered pregnancy rate 38.9%. Implantation rates per individual embryo transferred were 16.6% following fresh embryo transfer. A viable pregnancy was achieved by 14 of 28 women (50% cumulative pregnancy rate). We conclude that using donor oocytes and donor spermatozoa is efficacious and allows couples of whom both members suffer from severe gamete abnormalities and single functionally agonadal women an effective means of achieving pregnancy.  相似文献   

19.
20.
The French national register on in vitro fertilization (IVF) FIVNAT, which has collected most of the oocyte pick-ups realised in France since 1986 has allowed us to build a cohort of 35,714 couples, of which the first recovery took place between 1990 and 1994 and followed up to a pregnancy or to the 31st of december, 1996. The per recovery clinical pregnancy rate decreased from 20.2% on the first attempt to 17.4% on the second, and to less than 13% after the sixth. This evolution existed whatever the women's age class or the infertility diagnosis. The women's age remained the most important factor, since the cumulative pregnancy rate decreased from 60% for women aged less than 35 years to 17% for those aged more than 41 years. Among the indications, male infertility using spouse's semen had the poorest prognosis, especially for women aged more than 41 years (9.6%) whereas male infertility using donor's semen among women aged less than 35 years was associated to the best results (68%). It must be noticed than a high percentage of unpregnant women did not come again for a further recovery (40% to 50%). Then, the crude cumulative birth rate (24.4%) was far below the theoretical cumulative one(54.2%).  相似文献   

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