doi:10.1111/jog.12687
J. Obstet. Gynaecol. Res. Vol. 41, No. 8: 1223–1228, August 2015
Factors affecting occurrence of twin pregnancy after double embryo transfer on day 3 Myo Sun Kim1, Ji Hee Kim2, Byung Chul Jee1,3, Chang Suk Suh1,3 and Seok Hyun Kim2,3 1
Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam 2Department of Obstetrics and Gynecology, Seoul National University Hospital, Seoul 3Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea
Abstract Aim: The aim of this study was to identify the risk factors of twin gestation in fresh double day-3 embryo transfer cycles. Material and Methods: Out of a total of 386 cycles of fresh double embryo transfers on day 3 between 2006 and 2013 at a single center, 72 women with single intrauterine gestational sac (GS) (single-GS group) and 32 women with double GS (double-GS group) were identified. The patients’ clinical characteristics and laboratory results were extracted from electronic medical records and were compared. Results: The double-GS group had a significantly younger age (P = 0.012), and higher bodyweight (P = 0.033) compared with the single-GS group. The total number of blastomeres (P = 0.013) and cumulative embryo score (P = 0.012) were higher in the double-GS group. By receiver–operator curve analysis, maternal age ≤ 35 years, maternal bodyweight > 60 kg, total number of blastomeres > 14, and cumulative embryo score > 49 were the cut-off values to predict twin pregnancy. Among eight women with all four risk factors, the twin pregnancy rate was 87.5%. There was no twin pregnancy among seven women with no risk factors. Conclusion: Younger age, higher bodyweight, and better embryo quality are all associated with a higher incidence of twin pregnancy after double embryo transfer on day 3. Single embryo transfer might be advisable for couples with risk factors for twin pregnancy. Key words: double embryo transfer, in vitro fertilization, pregnancy, twins.
Introduction Over the past 30 years, various infertility therapies have resulted in increased conception of twin and higherorder multiple pregnancies. Between 1980 and 2005, the twinning rate rose from 18.9 to 32.1 per 1000 live births, and during the same time period, the number of live births from twin deliveries rose to nearly 50%.1 This extraordinary increase in multifetal births is a public health concern due to increased rates of preterm deliveries and thus decreased survival chances and increased risk of lifelong disability.2,3 Multiple embryo transfer, together with multiple implantation, during in vitro fertilization (IVF) increases
multiple pregnancy rates, thus increasing maternal and perinatal morbidity.4 Single-embryo transfer (SET) has been introduced to decrease multiple pregnancy, but the decrease in pregnancy rate and live birth rate have to be considered.5 It is reported that SET has about a one-third lower live birth rate relative to double-embryo transfer (DET).6 Therefore, the transfer of more than one embryo is still a preferred choice for most cases in order to achieve a favorable pregnancy outcome. There have been several studies to define embryo and cycle-specific parameters associated with twin pregnancy after DET. In a Chinese study, the women’s age and the number of high-quality embryos transferred were risk factors associated with twin pregnancy after
Received: November 11 2014. Accepted: January 4 2015. Reprint request to: Professor Byung Chul Jee, Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, 166 Gumi-ro, Bundang-gu, Seongnam 463-707, Korea. Email: [email protected]
© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
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IVF with DET.7 In another study from China, four variables – first attempt, good ovarian responsibility, higher number of top-quality embryos, and development stage score of the second-best embryo transferred – were correlated independently with twin pregnancy after DET.8 In a European study, the height of the women and the number of oocytes retrieved had an increased chance of twinning after DET.9 In a recent study from the USA, six risk factors were identified for twin live birth in day-3 cryopreserved DET cycles: (i) patient age < 35 years; (ii) intact survival of the lead embryo; (iii) resumption of mitosis; (iv) seven to eight viable cells in the non-lead embryo; (v) transfer of a lead embryo with ≥7 cells; and (vi) a sum of ≥14 viable cells in the two transferred embryos.10 If we know the risk factors associated with twinning after DET, SET would be preferred in the high-risk group, thus preventing the occurrence of twin gestation while maintaining a good clinical outcome. So far, there has been no report regarding the risk factors associated with twin pregnancy after DET in Korean women. This study aims to identify the risk factors for twin pregnancy in fresh day-3 DET cycles in Korean women.
Methods A single-institution, retrospective study was conducted at the Seoul National University Bundang Hospital with the approval of the Institutional Review Board. IVF cycles with fresh DET on day 3 performed between 2006 and 2013 were identified. IVF cycles needing surgical retrieval of sperm were excluded in this study. Clinical pregnancy was defined as detection of an identifiable intrauterine gestational sac(s) (GS). The patients’ demographics and clinical characteristics were collected through electronic medical records, which included the women’s age, height, weight, body mass index (BMI), parity, cause of infertility, cycle number, serum level of anti-Müllerian hormone (AMH), basal follicle-stimulating hormone (FSH), types and dose of gonadotrophins administered, peak serum estradiol level, and the quality of ejaculated sperm. Laboratory data, such as total or mature oocyte number, insemination method (conventional or intracytoplasmic sperm injection), fertilization rate, embryo grade, cell number of best-quality embryo, total cell number, and cumulative embryo score (CES), were also extracted. The quality of embryos was evaluated by morphological criteria based on the fragmentation degree and the regularity of blastomeres on day 3 after fertilization.
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The embryos were graded as follows: grade A, 0% anucleate fragments, regularity of blastomeres, and no apparent morphologic abnormalities; grade B, 50% anucleate fragments, irregularity of blastomeres, and apparent morphologic abnormalities. The CES was calculated by multiplication of morphological grade of the embryo (Grade A = 4, Grade B = 3, Grade C = 2, Grade D = 1) by the number of blastomeres. All statistical analyses were performed using SPSS 18. The data were analyzed using the Student’s t-test or the χ 2-test, as indicated. If the cell numbers were 14 (AUC 0.66, 95%CI 0.56–0.75), and CES > 49 (AUC 0.66, 95%CI 0.56–0.75) (Table 3). The twin pregnancy rates according to different variables were as follows: 39.6% (23/58) in women ≤ 35 years old and 19.7% (9/46) in women > 35 years old (P = 0.030, odds ratio [OR] 2.7, 95%CI 1.1–6.6); 50% (13/26) in women with bodyweight > 60 kg and 24.1% (14/58) in women with bodyweight ≤ 60 kg (P = 0.022, OR 3.1, 95%CI 1.2–8.3); 41.9% (26/62) in women with total number of blastomeres > 14 and 14.3% (6/42) in women with total number of blastomeres ≤ 14 (P = 0.004, OR 4.3, 95%CI 1.6–11.8); and 44.3% (27/61) in women with CES > 49 and 11.6% (5/43) in women with CES ≤ 49 (P = 0.001, OR 6.0, 95%CI 2.1–17.4). Among eight women with all four risk factors, the twin pregnancy rate was 87.5%. All seven women with no risk factors achieved singleton pregnancy.
Discussion In the present study, we demonstrated a close association of maternal age and bodyweight with twinning in DET. Women aged 35 years or less showed 2.7-fold higher occurrence of twinning, and the cut-off of maternal age was identical to that suggested in other previous studies.7,10 Women with bodyweight > 60 kg showed 3.1-fold higher occurrence of twinning, which has not been reported previously. Maternal height and BMI were not risk factors in the present study, although Groeneveld et al.9 suggested maternal height as a risk factor. In natural conception, it has been shown that features of body composition (in particular maternal height but also BMI) are associated with dizygotic twinning.11–13 Natural dizygotic twinning derives from multiple follicle growth and ovulation, followed by multiple implantations. It has been suggested that increased BMI or height results in multiple ovulation by higher levels of
© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
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Table 2 Comparison of semen and endometrial quality and IVF outcomes, including embryo morphologic parameters, between women in the single-GS and double-GS groups Single-GS group (n = 72)
Double-GS group (n = 32)
P
122 ± 148 62.2 ± 21.3 10.6 ± 4.8 18.6 ± 11.4 9.5 ± 2.3 33 (45.8%) 40 (55.6%)
170 ± 227 57.2 ± 20.8 10.3 ± 5.1 11.3 ± 11.2 10.4 ± 2.4 20 (62.5%) 14 (43.8%)
NS NS NS NS NS NS NS
2.6 ± 1.9 3.2 ± 2.3
3.5 ± 2.6 3.9 ± 2.9
NS NS
78.2 ± 26.2 75.4 ± 26.0 0.4 ± 1.4
84.3 ± 18.9 78.9 ± 20.4 0.7 ± 1.9
NS NS NS NS
31 (43.1%) 29 (40.3%) 12 (16.6%) 7.7 ± 1.0 14.1 ± 2.4 49.7 ± 13.2
17 (53.1%) 11 (34.4%) 4 (12.5%) 7.9 ± 0.9 15.3 ± 1.8 56.5 ± 11.1
Sperm concentration (million/mL) Sperm motility (%) Strict morphology (%) Sperm DNA fragmentation (%) Endometrial thickness (mm) Endometrial triple pattern (type C) Use of ICSI No. of fertilized oocytes Among initial mature oocyte Including in vitro matured oocyte Fertilization rate (%) Among initial mature oocyte Including in vitro matured oocyte No. of cryopreserved embryos No. of grade A embryos on day 3 2 1 0 No. of blastomeres in best-quality embryos Total no. of blastomeres† Cumulative embryo score†
NS 0.013 0.012
Mean ± standard deviation. †From two embryos transferred. GS, gestational sac; ICSI, intracytoplasmic sperm injection; IVF, in vitro fertilization; NS, not significant.
Table 3 Receiver–operator curve analysis for prediction of twin pregnancy
Maternal age (years) Maternal bodyweight (kg) Total no. of blastomeres† Cumulative embryo score†
Cut-off value
AUC
95%CI
Sensitivity
Specificity
LR+
LR–
≤35 >60 >14 >49
0.646 0.618 0.661 0.659
0.546–0.737 0.505–0.722 0.561–0.751 0.559–0.749
84.4 48.1 81.3 84.4
41.7 77.2 50.0 52.8
1.45 2.11 1.62 1.79
0.38 0.67 0.38 0.30
†
From two embryos transferred. AUC, area under the curve; CI, confidence interval; LR+, positive likelihood ratio; LR–, negative likelihood ratio.
FSH in obese women,11,12 but the exact mechanisms are largely unknown. In IVF conception, there has been only one report regarding an association between body composition and twinning rate: a Dutch group demonstrated that tall stature (>1.74 m) was related with dizygotic twining after IVF with DET.9 In that study, maternal height was significantly higher in the twin group (170.7 cm vs 169.3 cm, P = 0.043) although the difference was only 1.4 cm; maternal weight (64.8 kg vs 63.9 kg) and BMI (22.2 vs 22.3) were similar in the twin and singleton groups. In our study, maternal weight (60.6 kg vs 56.8 kg) was the only significant factor among maternal composition; maternal height (162.7 cm vs 160.1 cm) and BMI (23.1 vs 22.2) tended to be higher in the twin group, but this did not reach a statistical significance. It has been
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demonstrated that obesity is a fertility-decreasing factor, resulting in retained oocytes of diminished quality, decreased fertilization rates and poor pregnancy outcomes in IVF patients.14 However, it must be noted from our study that the BMI of women who conceived a singleton or twins were not excessively high (mean 22.5, range 17.9–31.6), indicating that only 10 women (9.6%) were overweight (BMI ≥ 25). Possibly, some overweight women may favor implantation with only minimal or even absent negative implications for fertility. The risk of natural dizygotic twinning has been reported to depend on maternal family history,13,15 but we were unable to obtain this data from the electronic medical records. Previous studies have shown that first attempt, good ovarian response8 and the number of oocytes retrieved9 were related to twinning after DET. However, our study
© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
Double day-3 ET and twin pregnancy
showed no effect in cycle number, number of oocytes retried, or marker of ovarian reserve. We found that embryo status significantly influences the twin pregnancy rate – especially the total cell number and CES. Compared with other previous reports, the number of top-grade embryos7,8 and cell number of the second-best-quality embryos8 did not have significance. Kaser et al.10 described a lead embryo with ≥7 cells and a sum of ≥14 viable cells as a risk factor. Our data match those of Kaser et al. in the total cell number as 14. Here, we additionally described the role of CES, where a CES score > 49 is a risk factor, which has been not reported previously. Numerous attempts have been done by the Korean government to decrease multiple pregnancies during IVF. The 2008 Korean Ministry of Health and Welfare guideline recommends the number of embryos transferred based on age ( 9. Other parameters, such as cycle number, maternal BMI, basal FSH and AMH, and semen quality, were not predictors. Our present work focused on identifying possible predictors for twinning in women who achieved clinical pregnancy after DET at day 3. The strengths of this study include the use of CES score for identifying risk factors and the identification of factors that favor SET rather than DET during day-3 ET. In conclusion, our analysis demonstrated four factors that influence twin pregnancy during DET on day 3. For women aged ≤ 35 years, with bodyweight > 60 kg, total number of blastomeres > 14, and a CES > 49, SET would be preferred for the achievement of singleton pregnancy. Further prospective studies are needed to demonstrate whether SET in women with these risk factors would really improve IVF outcome and reduce the twinning rate.
Acknowledgments This work was supported by grant no. A120043 from the Korea Health Care Technology R&D Project, Ministry of Health and Welfare, Korea.
Disclosure The authors have nothing to disclose.
References 1. Martin JA, Hamilton BE, Sutton PD, Ventura SJ, Mathews TJ, Osterman MJ. Births: final data for 2008. Natl Vital Stat Rep 2010; 59: 3–71.
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2. Thurin A, Hausken J, Hillensjo T et al. Elective single-embryo transfer versus double-embryo transfer in in vitro fertilization. N Engl J Med 2004; 351: 2392–2402. 3. Grady R, Alavi N, Vale R, Khandwala M, McDonald SD. Elective single embryo transfer and perinatal outcomes: A systematic review and meta-analysis. Fertil Steril. 2012; 97: 324–331. 4. Pandian Z, Marjoribanks J, Ozturk O, Serour G, Bhattacharya S. Number of embryos for transfer following in vitro fertilisation or intra-cytoplasmic sperm injection. Cochrane Database Syst Rev 2013; 7: CD003416. 5. Baruffi RL, Mauri AL, Petersen CG et al. Single-embryo transfer reduces clinical pregnancy rates and live births in fresh IVF and intracytoplasmic sperm injection (ICSI) cycles: A meta-analysis. Reprod Biol Endocrinol 2009; 7: 36. 6. Roberts SA, McGowan L, Mark Hirst W et al. Reducing the incidence of twins from IVF treatments: Predictive modelling from a retrospective cohort. Hum Reprod 2011; 26: 569–575. 7. Xu WH, Tong XM, Zhu HY, Lin XN, Jiang LY, Zhang SY. Risk factors associated with twin pregnancy in double embryo transfer. Zhonghua yi xue za zhi 2011; 91: 2615–2618. 8. Niu ZH, Feng Y, Zhang AJ, Zhang HQ, Sun YJ, Lu XW. Factors related to occurrence of twin pregnancy after double-embryo transfer in vitro fertilization cycles. Zhonghua fu chan ke za zhi 2009; 44: 413–417. 9. Groeneveld E, Lambers MJ, Stakelbeek ME et al. Factors associated with dizygotic twinning after IVF treatment with double embryo transfer. Hum Reprod 2012; 27: 2966–2970.
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10. Kaser DJ, Missmer SA, Correia KF, Ceyhan ST, Hornstein MD, Racowsky C. Predictors of twin live birth following cryopreserved double embryo transfer on day 3. J Assist Reprod Genet 2013; 30: 1023–1030. 11. Basso O, Nohr EA, Christensen K, Olsen J. Risk of twinning as a function of maternal height and body mass index. JAMA 2004; 291: 1564–1566. 12. Reddy UM, Branum AM, Klebanoff MA. Relationship of maternal body mass index and height to twinning. Obstet Gynecol 2005; 105: 593–597. 13. Hoekstra C, Willemsen G, van Beijsterveldt CE, Lambalk CB, Montgomery GW, Boomsma DI. Body composition, smoking, and spontaneous dizygotic twinning. Fertil Steril 2010; 93: 885–893. 14. Robker RL. Evidence that obesity alters the quality of oocytes and embryos. Pathophysiology 2008; 15: 115–121. 15. Beemsterboer SN, Homburg R, Gorter NA, Schats R, Hompes PG, Lambalk CB. The paradox of declining fertility but increasing twinning rates with advancing maternal age. Hum Reprod 2006; 21: 1531–1532. 16. Committee for Assisted Reproductive Technology KSoOG, Choi YM, Chun SS, Han HD et al. Current status of assisted reproductive technology in Korea, 2009. Obstet Gynecol Sci 2013; 56: 353–361. 17. Vilska S, Tiitinen A, Hyden-Granskog C, Hovatta O. Elective transfer of one embryo results in an acceptable pregnancy rate and eliminates the risk of multiple birth. Hum Reprod 1999; 14: 2392–2395. 18. Gerris JM. Single embryo transfer and IVF/ICSI outcome: A balanced appraisal. Hum Reprod Update 2005; 11: 105–121.
© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
J. Obstet. Gynaecol. Res. Vol. 41, No. 8: 1223–1228, August 2015
Factors affecting occurrence of twin pregnancy after double embryo transfer on day 3 Myo Sun Kim1, Ji Hee Kim2, Byung Chul Jee1,3, Chang Suk Suh1,3 and Seok Hyun Kim2,3 1
Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam 2Department of Obstetrics and Gynecology, Seoul National University Hospital, Seoul 3Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea
Abstract Aim: The aim of this study was to identify the risk factors of twin gestation in fresh double day-3 embryo transfer cycles. Material and Methods: Out of a total of 386 cycles of fresh double embryo transfers on day 3 between 2006 and 2013 at a single center, 72 women with single intrauterine gestational sac (GS) (single-GS group) and 32 women with double GS (double-GS group) were identified. The patients’ clinical characteristics and laboratory results were extracted from electronic medical records and were compared. Results: The double-GS group had a significantly younger age (P = 0.012), and higher bodyweight (P = 0.033) compared with the single-GS group. The total number of blastomeres (P = 0.013) and cumulative embryo score (P = 0.012) were higher in the double-GS group. By receiver–operator curve analysis, maternal age ≤ 35 years, maternal bodyweight > 60 kg, total number of blastomeres > 14, and cumulative embryo score > 49 were the cut-off values to predict twin pregnancy. Among eight women with all four risk factors, the twin pregnancy rate was 87.5%. There was no twin pregnancy among seven women with no risk factors. Conclusion: Younger age, higher bodyweight, and better embryo quality are all associated with a higher incidence of twin pregnancy after double embryo transfer on day 3. Single embryo transfer might be advisable for couples with risk factors for twin pregnancy. Key words: double embryo transfer, in vitro fertilization, pregnancy, twins.
Introduction Over the past 30 years, various infertility therapies have resulted in increased conception of twin and higherorder multiple pregnancies. Between 1980 and 2005, the twinning rate rose from 18.9 to 32.1 per 1000 live births, and during the same time period, the number of live births from twin deliveries rose to nearly 50%.1 This extraordinary increase in multifetal births is a public health concern due to increased rates of preterm deliveries and thus decreased survival chances and increased risk of lifelong disability.2,3 Multiple embryo transfer, together with multiple implantation, during in vitro fertilization (IVF) increases
multiple pregnancy rates, thus increasing maternal and perinatal morbidity.4 Single-embryo transfer (SET) has been introduced to decrease multiple pregnancy, but the decrease in pregnancy rate and live birth rate have to be considered.5 It is reported that SET has about a one-third lower live birth rate relative to double-embryo transfer (DET).6 Therefore, the transfer of more than one embryo is still a preferred choice for most cases in order to achieve a favorable pregnancy outcome. There have been several studies to define embryo and cycle-specific parameters associated with twin pregnancy after DET. In a Chinese study, the women’s age and the number of high-quality embryos transferred were risk factors associated with twin pregnancy after
Received: November 11 2014. Accepted: January 4 2015. Reprint request to: Professor Byung Chul Jee, Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, 166 Gumi-ro, Bundang-gu, Seongnam 463-707, Korea. Email: [email protected]
© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
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IVF with DET.7 In another study from China, four variables – first attempt, good ovarian responsibility, higher number of top-quality embryos, and development stage score of the second-best embryo transferred – were correlated independently with twin pregnancy after DET.8 In a European study, the height of the women and the number of oocytes retrieved had an increased chance of twinning after DET.9 In a recent study from the USA, six risk factors were identified for twin live birth in day-3 cryopreserved DET cycles: (i) patient age < 35 years; (ii) intact survival of the lead embryo; (iii) resumption of mitosis; (iv) seven to eight viable cells in the non-lead embryo; (v) transfer of a lead embryo with ≥7 cells; and (vi) a sum of ≥14 viable cells in the two transferred embryos.10 If we know the risk factors associated with twinning after DET, SET would be preferred in the high-risk group, thus preventing the occurrence of twin gestation while maintaining a good clinical outcome. So far, there has been no report regarding the risk factors associated with twin pregnancy after DET in Korean women. This study aims to identify the risk factors for twin pregnancy in fresh day-3 DET cycles in Korean women.
Methods A single-institution, retrospective study was conducted at the Seoul National University Bundang Hospital with the approval of the Institutional Review Board. IVF cycles with fresh DET on day 3 performed between 2006 and 2013 were identified. IVF cycles needing surgical retrieval of sperm were excluded in this study. Clinical pregnancy was defined as detection of an identifiable intrauterine gestational sac(s) (GS). The patients’ demographics and clinical characteristics were collected through electronic medical records, which included the women’s age, height, weight, body mass index (BMI), parity, cause of infertility, cycle number, serum level of anti-Müllerian hormone (AMH), basal follicle-stimulating hormone (FSH), types and dose of gonadotrophins administered, peak serum estradiol level, and the quality of ejaculated sperm. Laboratory data, such as total or mature oocyte number, insemination method (conventional or intracytoplasmic sperm injection), fertilization rate, embryo grade, cell number of best-quality embryo, total cell number, and cumulative embryo score (CES), were also extracted. The quality of embryos was evaluated by morphological criteria based on the fragmentation degree and the regularity of blastomeres on day 3 after fertilization.
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The embryos were graded as follows: grade A, 0% anucleate fragments, regularity of blastomeres, and no apparent morphologic abnormalities; grade B, 50% anucleate fragments, irregularity of blastomeres, and apparent morphologic abnormalities. The CES was calculated by multiplication of morphological grade of the embryo (Grade A = 4, Grade B = 3, Grade C = 2, Grade D = 1) by the number of blastomeres. All statistical analyses were performed using SPSS 18. The data were analyzed using the Student’s t-test or the χ 2-test, as indicated. If the cell numbers were 14 (AUC 0.66, 95%CI 0.56–0.75), and CES > 49 (AUC 0.66, 95%CI 0.56–0.75) (Table 3). The twin pregnancy rates according to different variables were as follows: 39.6% (23/58) in women ≤ 35 years old and 19.7% (9/46) in women > 35 years old (P = 0.030, odds ratio [OR] 2.7, 95%CI 1.1–6.6); 50% (13/26) in women with bodyweight > 60 kg and 24.1% (14/58) in women with bodyweight ≤ 60 kg (P = 0.022, OR 3.1, 95%CI 1.2–8.3); 41.9% (26/62) in women with total number of blastomeres > 14 and 14.3% (6/42) in women with total number of blastomeres ≤ 14 (P = 0.004, OR 4.3, 95%CI 1.6–11.8); and 44.3% (27/61) in women with CES > 49 and 11.6% (5/43) in women with CES ≤ 49 (P = 0.001, OR 6.0, 95%CI 2.1–17.4). Among eight women with all four risk factors, the twin pregnancy rate was 87.5%. All seven women with no risk factors achieved singleton pregnancy.
Discussion In the present study, we demonstrated a close association of maternal age and bodyweight with twinning in DET. Women aged 35 years or less showed 2.7-fold higher occurrence of twinning, and the cut-off of maternal age was identical to that suggested in other previous studies.7,10 Women with bodyweight > 60 kg showed 3.1-fold higher occurrence of twinning, which has not been reported previously. Maternal height and BMI were not risk factors in the present study, although Groeneveld et al.9 suggested maternal height as a risk factor. In natural conception, it has been shown that features of body composition (in particular maternal height but also BMI) are associated with dizygotic twinning.11–13 Natural dizygotic twinning derives from multiple follicle growth and ovulation, followed by multiple implantations. It has been suggested that increased BMI or height results in multiple ovulation by higher levels of
© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
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Table 2 Comparison of semen and endometrial quality and IVF outcomes, including embryo morphologic parameters, between women in the single-GS and double-GS groups Single-GS group (n = 72)
Double-GS group (n = 32)
P
122 ± 148 62.2 ± 21.3 10.6 ± 4.8 18.6 ± 11.4 9.5 ± 2.3 33 (45.8%) 40 (55.6%)
170 ± 227 57.2 ± 20.8 10.3 ± 5.1 11.3 ± 11.2 10.4 ± 2.4 20 (62.5%) 14 (43.8%)
NS NS NS NS NS NS NS
2.6 ± 1.9 3.2 ± 2.3
3.5 ± 2.6 3.9 ± 2.9
NS NS
78.2 ± 26.2 75.4 ± 26.0 0.4 ± 1.4
84.3 ± 18.9 78.9 ± 20.4 0.7 ± 1.9
NS NS NS NS
31 (43.1%) 29 (40.3%) 12 (16.6%) 7.7 ± 1.0 14.1 ± 2.4 49.7 ± 13.2
17 (53.1%) 11 (34.4%) 4 (12.5%) 7.9 ± 0.9 15.3 ± 1.8 56.5 ± 11.1
Sperm concentration (million/mL) Sperm motility (%) Strict morphology (%) Sperm DNA fragmentation (%) Endometrial thickness (mm) Endometrial triple pattern (type C) Use of ICSI No. of fertilized oocytes Among initial mature oocyte Including in vitro matured oocyte Fertilization rate (%) Among initial mature oocyte Including in vitro matured oocyte No. of cryopreserved embryos No. of grade A embryos on day 3 2 1 0 No. of blastomeres in best-quality embryos Total no. of blastomeres† Cumulative embryo score†
NS 0.013 0.012
Mean ± standard deviation. †From two embryos transferred. GS, gestational sac; ICSI, intracytoplasmic sperm injection; IVF, in vitro fertilization; NS, not significant.
Table 3 Receiver–operator curve analysis for prediction of twin pregnancy
Maternal age (years) Maternal bodyweight (kg) Total no. of blastomeres† Cumulative embryo score†
Cut-off value
AUC
95%CI
Sensitivity
Specificity
LR+
LR–
≤35 >60 >14 >49
0.646 0.618 0.661 0.659
0.546–0.737 0.505–0.722 0.561–0.751 0.559–0.749
84.4 48.1 81.3 84.4
41.7 77.2 50.0 52.8
1.45 2.11 1.62 1.79
0.38 0.67 0.38 0.30
†
From two embryos transferred. AUC, area under the curve; CI, confidence interval; LR+, positive likelihood ratio; LR–, negative likelihood ratio.
FSH in obese women,11,12 but the exact mechanisms are largely unknown. In IVF conception, there has been only one report regarding an association between body composition and twinning rate: a Dutch group demonstrated that tall stature (>1.74 m) was related with dizygotic twining after IVF with DET.9 In that study, maternal height was significantly higher in the twin group (170.7 cm vs 169.3 cm, P = 0.043) although the difference was only 1.4 cm; maternal weight (64.8 kg vs 63.9 kg) and BMI (22.2 vs 22.3) were similar in the twin and singleton groups. In our study, maternal weight (60.6 kg vs 56.8 kg) was the only significant factor among maternal composition; maternal height (162.7 cm vs 160.1 cm) and BMI (23.1 vs 22.2) tended to be higher in the twin group, but this did not reach a statistical significance. It has been
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demonstrated that obesity is a fertility-decreasing factor, resulting in retained oocytes of diminished quality, decreased fertilization rates and poor pregnancy outcomes in IVF patients.14 However, it must be noted from our study that the BMI of women who conceived a singleton or twins were not excessively high (mean 22.5, range 17.9–31.6), indicating that only 10 women (9.6%) were overweight (BMI ≥ 25). Possibly, some overweight women may favor implantation with only minimal or even absent negative implications for fertility. The risk of natural dizygotic twinning has been reported to depend on maternal family history,13,15 but we were unable to obtain this data from the electronic medical records. Previous studies have shown that first attempt, good ovarian response8 and the number of oocytes retrieved9 were related to twinning after DET. However, our study
© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
Double day-3 ET and twin pregnancy
showed no effect in cycle number, number of oocytes retried, or marker of ovarian reserve. We found that embryo status significantly influences the twin pregnancy rate – especially the total cell number and CES. Compared with other previous reports, the number of top-grade embryos7,8 and cell number of the second-best-quality embryos8 did not have significance. Kaser et al.10 described a lead embryo with ≥7 cells and a sum of ≥14 viable cells as a risk factor. Our data match those of Kaser et al. in the total cell number as 14. Here, we additionally described the role of CES, where a CES score > 49 is a risk factor, which has been not reported previously. Numerous attempts have been done by the Korean government to decrease multiple pregnancies during IVF. The 2008 Korean Ministry of Health and Welfare guideline recommends the number of embryos transferred based on age ( 9. Other parameters, such as cycle number, maternal BMI, basal FSH and AMH, and semen quality, were not predictors. Our present work focused on identifying possible predictors for twinning in women who achieved clinical pregnancy after DET at day 3. The strengths of this study include the use of CES score for identifying risk factors and the identification of factors that favor SET rather than DET during day-3 ET. In conclusion, our analysis demonstrated four factors that influence twin pregnancy during DET on day 3. For women aged ≤ 35 years, with bodyweight > 60 kg, total number of blastomeres > 14, and a CES > 49, SET would be preferred for the achievement of singleton pregnancy. Further prospective studies are needed to demonstrate whether SET in women with these risk factors would really improve IVF outcome and reduce the twinning rate.
Acknowledgments This work was supported by grant no. A120043 from the Korea Health Care Technology R&D Project, Ministry of Health and Welfare, Korea.
Disclosure The authors have nothing to disclose.
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© 2015 The Authors Journal of Obstetrics and Gynaecology Research © 2015 Japan Society of Obstetrics and Gynecology
