Potential risk factors between immediate and delayed FET groups in the entire and propensity score-matched cohort
A total of 2128 HOR patients adopting freeze-all strategy underwent their first IVF/ICSI cycle (Fig. 1). There are 1130 patients in the immediate FET group and 998 patients in the delayed FET group. Patients’ and IVF characteristics in the immediate and delayed FET groups, which as potential risk factors, were presented in Table 1. Before matching, the distribution of these risk factors were not absolutely balanced. The distribution of COH protocol, number of embryo transferred, embryo stage and multiple pregnancies were significantly different between the two groups (P < 0.05). No significant differences were found in maternal age, body mass index (BMI), insemination method, and infertility causes (P > 0.05). We obtained 1366 patients by propensity score matching, and all potential risk factors and the pregnancy outcome of multiple pregnancies among them are balanced and comparable (Table 1).
Table 1
Baseline characteristics of immediate and delayed FET groups in the entire and propensity score-matched cohorts
Potential risk factors
|
Entire cohort
(n = 2128)
|
P-value
|
Propensity score-matched cohort*
(n = 1366)
|
P-value
|
Immediate FETa
|
Delayed FETb
|
Immediate FETa
|
Delayed FETb
|
(n = 1130 )
|
(n = 998)
|
|
(n = 683)
|
(n = 683)
|
|
Maternal age (years)
|
|
|
0.455
|
|
|
1.000
|
≤ 34
|
976 (86.4)
|
851 (85.3)
|
|
622 (91.1)
|
622 (91.1)
|
|
35–37
|
114 (10.1)
|
101 (10.1)
|
|
48 (7.0)
|
48 (7.0)
|
|
≥ 38
|
40 (3.5)
|
46 (4.6)
|
|
13 (1.9)
|
13 (1.9)
|
|
BMI (kg/m2)
|
|
|
0.431
|
|
|
1.000
|
< 18.5
|
70 (6.2)
|
58 (5.8)
|
|
465 (68.1)
|
465 (68.1)
|
|
18.5–24.9
|
750 (66.4)
|
641 (64.2)
|
|
22 (3.2)
|
22 (3.2)
|
|
≥ 25
|
310 (27.4)
|
299 (30.0)
|
|
196 (28.7)
|
196 (28.7)
|
|
Insemination method
|
|
|
0.056
|
|
|
1.000
|
IVF
|
814 (72.0)
|
681 (68.2)
|
|
490 (71.7)
|
490 (71.7)
|
|
ICSI
|
316 (28.0)
|
317 (31.8)
|
193 (28.3)
|
193 (28.3)
|
COH protocol
|
|
|
0.000
|
|
|
1.000
|
GnRH-ant protocol
|
485 (42.9)
|
433 (43.4)
|
0.273#
|
284 (41.6)
|
284 (41.6)
|
0.651#
|
HCG trigger
|
330 (68.0)
|
306 (70.7)
|
|
199 (70.1)
|
199 (70.1)
|
|
GnRH-a trigger
|
137 (28.2)
|
105 (24.2)
|
79 (27.8)
|
79 (27.8)
|
Double trigger
|
18 (3.7)
|
22 (5.1)
|
6 (2.1)
|
6 (2.1)
|
Short acting GnRH-a protocol
|
566 (50.1)
|
434 (43.5)
|
|
335 (49.0)
|
335 (49.0)
|
|
Long acting GnRH-a protocol
|
79 (7.0)
|
131 (13.1)
|
|
64 (9.4)
|
64 (9.4)
|
|
Number of embryo transfer
|
|
|
0.000
|
|
|
1.000
|
1
|
265 (23.5)
|
416 (41.7)
|
|
208 (30.5)
|
208 (30.5)
|
|
2
|
865 (76.5)
|
582 (58.3)
|
475 (69.5)
|
475 (69.5)
|
Embryo stage
|
|
|
0.000
|
|
|
1.000
|
Cleavage stage
|
711 (62.9)
|
499 (50.0)
|
|
418 (61.2)
|
418 (61.2)
|
|
Blastocyst stage
|
419 (37.1)
|
499 (50.0)
|
265 (38.8)
|
265 (38.8)
|
Cause of infertility
|
Tubal factor
|
720 (63.7)
|
630 (63.1)
|
0.778
|
456 (66.8)
|
456 (66.8)
|
1.000
|
Ovulatory disorder
|
304 (26.9)
|
257 (25.8)
|
0.548
|
167 (24.5)
|
167 (24.5)
|
1.000
|
Male factor
|
452 (40.0)
|
420 (42.1)
|
0.329
|
273 (40.0)
|
273 (40.0)
|
1.000
|
Unexplained factor
|
48 (4.2)
|
46 (4.6)
|
0.686
|
16 (2.3)
|
16 (2.3)
|
1.000
|
Multiple pregnancies
|
216 (19.1)
|
137 (13.7)
|
0.001
|
106 (15.5)
|
112 (16.4)
|
0.658
0.658
|
Abbreviations
BMI, body mass index; COH, controlled ovarian hyperstimulation; FET, frozen embryo transfer; GnRH-a, gonadotrophin-releasing hormone agonist; GnRH-ant, gonadotrophin-releasing hormone antagonist; HRT, hormone replacement therapy; IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection. Data are presented as number (%).
aImmediate FET and bDelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards.
*The predictors of propensity score matching were maternal age, BMI, insemination method, COH protocol, number of embryo transferred, embryo stage and cause of infertility. The match tolerance was set to 0.000001. Categorical variables were compared with χ2 test.
# P value of differences of different trigger drugs in GnRH-ant protocol.
Multivariable logistic regression analysis on FET timing and potential risk factors for pregnancy outcomes in the entire before-matching cohort
Multivariable logistic regression analysis on the entire before-matching cohort demonstrated no statistically differences on pregnancy outcomes between the immediate and delayed FET groups [CPR, adjusted odd ratio (OR), 0.942, 95% confidence interval (CI), 0.784–1.133; SAR, adjusted OR, 1.118, 95% Cl (0.771–1.623); LBR, adjusted OR, 1.060, 95% Cl (0.886–1.267)] (P > 0.05), which were adjusted for maternal age, BMI, COH protocol, insemination method, number of embryo transferred, embryo stage, trigger type, and cause of infertility (Table 2).
Table 2
Multivariable logistic regression analysis on potential risk factors for pregnancy outcomes in the entire cohort
Potential risk factor variables
|
Adjusted OR* (95% CI)
|
P-value
|
Clinical pregnancy
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
0.942 (0.784–1.133)
|
NS
|
Age (35–37 versus ≤ 34)
|
0.922 (0.685–1.241)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.414 (0.263–0.650)
|
P < 0.001
|
BMI (< 18.5 versus 18.5–24.9)
|
1.078 (0.734–1.585)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
1.121 (0.911–1.380)
|
NS
|
COH protocol (short-acting GnRH-a versus GnRH-ant)
|
1.240 (0.998–1.542)
|
NS
|
COH protocol (long-acting GnRH-a versus GnRH-ant)
|
1.376 (0.983–1.928)
|
NS
|
Trigger type (GnRH-a trigger versus HCG trigger)
|
1.279 (0.933–1.754 )
|
NS
|
Trigger type (Double trigger versus HCG trigger)
|
2.714 (1.217–6.053)
|
P < 0.05
|
Insemination method (ICSI versus IVF)
|
0.880 (0.691–1.122)
|
NS
|
Number of embryo transferred (2 versus 1)
|
1.534 (1.122–2.099)
|
P < 0.01
|
Embryo stage (blastocyst versus cleavage)
|
2.637 (1.968–3.533)
|
P < 0.001
|
Tubal factor (yes versus no)
|
1.114 (0.879–1.410)
|
NS
|
Ovulatory disorder (yes versus no)
|
1.107 (0.874–1.401)
|
NS
|
Male factor (yes versus no)
|
1.174 (0.926–1.487)
|
NS
|
Unexplained factor (yes versus no)
|
1.475 (0.884–2.460)
|
NS
|
Spontaneous abortion
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
1.118 (0.771–1.623 )
|
NS
|
Age (35–37 versus ≤ 34)
|
1.083 (0.690–1.699)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
1.980 (0.630–2.276)
|
NS
|
BMI (< 18.5 versus 18.5–24.9)
|
0.971 (0.507–1.859)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
1.788 (1.337–2.393)
|
P < 0.001
|
COH protocol (short-acting GnRH-a versus GnRH-ant)
|
0.826 (0.590–1.157)
|
NS
|
COH protocol (long-acting GnRH-a versus GnRH-ant)
|
1.239 (0.760–2.018)
|
NS
|
Trigger type (GnRH-a trigger versus HCG trigger)
|
0.875 (0.553–1.385)
|
NS
|
Trigger type (Double trigger versus HCG trigger)
|
1.458 (0.640–3.326)
|
NS
|
Insemination method (ICSI versus IVF)
|
1.118 (0.771–1.623)
|
NS
|
Number of embryo transferred (2 versus 1)
|
0.951 (0.618–1.465)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
1.188 (0.789–1.788)
|
NS
|
Tubal factor (yes versus no)
|
0.730 (0.515–1.034)
|
NS
|
Ovulatory disorder (yes versus no)
|
1.332 (0.947–1.873)
|
NS
|
Male factor (yes versus no)
|
0.709 (0.491–1.022)
|
NS
|
Unexplained factor (yes versus no)
|
0.750 (0.350–1.609)
|
NS
|
Live birth
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
1.060 (0.886–1.267)
|
NS
|
Age (35–37 versus ≤ 34)
|
0.928 (0.695–1.240)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.357 (0.217–0.587)
|
P < 0.001
|
BMI (< 18.5 versus 18.5–24.9)
|
1.092 (0.753–1.583)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
0.842 (0.689–1.029)
|
NS
|
COH protocol (short-acting GnRH-a versus GnRH-ant)
|
1.252 (1.012–1.550)
|
P < 0.05
|
COH protocol (long-acting GnRH-a versus GnRH-ant)
|
1.253 (0.904–1.737)
|
NS
|
Trigger type (GnRH-a trigger versus HCG trigger)
|
1.331 (0.979–1.809)
|
NS
|
Trigger type (Double trigger versus HCG trigger)
|
1.943 (0.995–3.794)
|
NS
|
Insemination method (ICSI versus IVF)
|
0.897 (0.709–1.136)
|
NS
|
Number of embryo transferred (2 versus 1)
|
1.420 (1.064–1.895)
|
P < 0.05
|
Embryo stage (blastocyst versus cleavage)
|
2.246 (1.717–2.937)
|
P < 0.001
|
Tubal factor (yes versus no)
|
1.302 (1.035–1.639)
|
P < 0.05
|
Ovulatory disorder (yes versus no)
|
0.947 (0.754–1.189)
|
NS
|
Male factor (yes versus no)
|
1.326 (1.054–1.669)
|
P < 0.05
|
Unexplained factor (yes versus no)
|
1.575 (0.970–2.559)
|
NS
|
Abbreviations BMI, body mass index; FET, frozen embryo transfer; GnRH-a, gonadotrophin-releasing hormone agonist; GnRH-ant, gonadotrophin-releasing hormone antagonist; IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection; OR, odds ratio; CI, confidence interval; NS, not significant.
aImmediate FET and bdelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards.
*Using the multivariable logistic regression and adjusting for maternal age, BMI, insemination method, COH protocol, trigger type, number of embryo transferred, embryo stage and cause of infertility.
Immediate FET versus delayed FET cycles on pregnancy outcomes in propensity score-matched cohort
The CPR (60.5% versus 63.5%), SAR (11.6% versus 12.3%), LBR (48.0% versus 49.3%) had no significant differences between the immediate and delayed FET groups in the propensity score-matched cohort (P > 0.05), which were detailed in Table 3.
Table 3
Pregnancy outcomes of immediate FETa and delayed FETb groups in the propensity score-matched cohort
Pregnancy outcomes
|
Immediate FETa
(n = 683)
|
Delayed FETb
(n = 683)
|
P-value
|
Clinical pregnancy
|
413 (60.5)
|
434 (63.5)
|
0.242
|
Spontaneous abortion
|
79 (11.6)
|
84 (12.3)
|
0.676
|
Live birth
|
328 (48.0)
|
337 (49.3)
|
0.626
|
Abbreviations FET, frozen embryo transfer.
aImmediate FET and bDelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards. Data are presented as number (%).
Differences between the groups were evaluated by χ2 test.
Subgroup analysis on immediate FET versus delayed FET on pregnancy outcomes in different COH protocol cohorts
To investigate the effect of FET timing on pregnancy outcomes in different COH protocols, multivariable logistic regression were performed on each COH protocol cohort, including 918 patients in antagonist protocol, 1000 patients in short-acting GnRH-a long protocol, and 210 patients in long-acting GnRH-a long protocol. Multivariable logistic regression analysis demonstrated no statistically differences on pregnancy outcomes between the immediate and delayed FET groups in short acting GnRH-a long protocol (CPR, adjusted OR, 0.998, 95% CI, 0.761–1.308; SAR, adjusted OR, 1.350, 95% Cl, 0.854–2.135; LBR, adjusted OR, 0.939, 95% Cl, 0.723–1.220) (P > 0.05), which were adjusted for maternal age, BMI, insemination method, number of embryo transferred, embryo stage and cause of infertility. However, the SAR of the immediate FET group was lower than that of the delayed FET group in the GnRH-ant protocol (adjusted for maternal age, BMI, trigger type, insemination method, embryo stage, number of embryo transferred, and cause of infertility) and long-acting GnRH-a long protocol (adjusted for maternal age, BMI) (GnRH-ant protocol, adjusted OR, 0.646, 95% CI, 0.432–0.966; long-acting GnRH-a long protocol, adjusted OR, 0.375, 95% CI, 0.142–0.990) (P < 0.05). No significant differences were found on CPRs and LBRs in GnRH-ant and long-acting GnRH-a long protocols (P > 0.05) (Table 4–6).
Table 4
Multivariable logistic regression analysis on potential risk factors for pregnancy outcomes in GnRH-ant protocol
Potential risk factor variables
|
Adjusted OR* (95% CI)
|
P-value
|
Clinical pregnancy
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
0.957 (0.723–1.267)
|
NS
|
Age (35–37 versus ≤ 34)
|
0.799 (0.502–1.270)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.387 (0.211–0.708)
|
P < 0.01
|
BMI (< 18.5 versus 18.5–24.9)
|
0.781 (0.424–1.439)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
0.980 (0.731–1.314)
|
NS
|
Trigger type (GnRH-a trigger versus HCG trigger)
|
1.228 (0.819–1.693)
|
NS
|
Trigger type (Double trigger versus HCG trigger)
|
2.562 (1.144–5.740)
|
P < 0.05
|
Insemination method (ICSI versus IVF)
|
1.005 (0.696–1.451)
|
NS
|
Number of embryo transferred (2 versus 1)
|
1.729 (1.043–2.865)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
3.069 (1.883–5.003)
|
P < 0.001
|
Tubal factor (yes versus no)
|
1.043 (0.745–1.461)
|
NS
|
Ovulatory disorder (yes versus no)
|
1.242 (0.909–1.695)
|
NS
|
Male factor (yes versus no)
|
1.012 (0.720–1.423)
|
NS
|
Unexplained factor (yes versus no)
|
1.267 (0.622–2.581)
|
NS
|
Spontaneous abortion
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
0.646 (0.432–0.966)
|
P < 0.05
|
Age (35–37 versus ≤ 34)
|
1.203 (0.621–2.330)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
1.516 (0.701–3.280)
|
NS
|
BMI (< 18.5 versus 18.5–24.9)
|
0.716 (0.245–2.093)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
1.399 (0.934–2.095)
|
NS
|
Trigger type (GnRH-a trigger versus HCG trigger)
|
0.906 (0.569–1.443)
|
NS
|
Trigger type (Double trigger versus HCG trigger)
|
1.410 (0.615–3.235)
|
NS
|
Insemination method (ICSI versus IVF)
|
1.271 (0.756–2.136)
|
NS
|
Number of embryo transferred (2 versus 1)
|
1.039 (0.556–1.943)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
1.543 (0.838–2.840)
|
NS
|
Tubal factor (yes versus no)
|
0.874 (0.550–1.389)
|
NS
|
Ovulatory disorder (yes versus no)
|
1.583 (1.017–2.465)
|
P < 0.05
|
Male factor (yes versus no)
|
0.794 (0.483–1.305)
|
NS
|
Unexplained factor (yes versus no)
|
0.977 (0.353–2.707)
|
NS
|
Live birth
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
1.216 (0.923–1.601)
|
NS
|
Age (35–37 versus ≤ 34)
|
0.760 (0.478–1.208)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.248 (0.121–0.511)
|
P < 0.001
|
BMI (< 18.5 versus 18.5–24.9)
|
0.883 (0.484–1.611)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
0.799 (0.600-1.064)
|
NS
|
Trigger type (GnRH-a trigger versus HCG trigger)
|
1.253 (0.918–1.710)
|
NS
|
Trigger type (Double trigger versus HCG trigger)
|
1.862 (0.949–3.653)
|
NS
|
Insemination method (ICSI versus IVF)
|
0.942 (0.657–1.350)
|
NS
|
Number of embryo transferred (2 versus 1)
|
1.629 (1.024–2.593)
|
P < 0.05
|
Embryo stage (blastocyst versus cleavage)
|
2.391 (1.528–3.740)
|
P < 0.001
|
Tubal factor (yes versus no)
|
1.145 (0.825–1.588)
|
NS
|
Ovulatory disorder (yes versus no)
|
0.993 (0.734–1.345)
|
NS
|
Male factor (yes versus no)
|
1.154 (0.826–1.610)
|
NS
|
Unexplained factor (yes versus no)
|
1.235 (0.621–2.455)
|
NS
|
Abbreviations BMI, body mass index; FET, frozen embryo transfer; GnRH-a, gonadotrophin-releasing hormone agonist; GnRH-ant, gonadotrophin-releasing hormone antagonist; IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection; OR, odds ratio; CI, confidence interval; NS, not significant.
aImmediate FET and bdelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards.
*Using the multivariable logistic regression and adjusting for maternal age, BMI, insemination method, trigger type, number of embryo transferred, embryo stage and cause of infertility.
Table 5
Multivariable logistic regression analysis on risk factors for pregnancy outcomes in short-acting GnRH-a long protocol
Potential risk factor variables
|
Adjusted OR* (95% CI)
|
P-value
|
Clinical pregnancy
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
0.998 (0.761–1.308)
|
NS
|
Age (35–37 versus ≤ 34)
|
0.979 (0.632–1.518)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.406 (0.191–0.863)
|
P < 0.05
|
BMI (< 18.5 versus 18.5–24.9)
|
1.399 (0.797–2.455)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
1.272 (0.914–1.770)
|
NS
|
Insemination method (ICSI versus IVF)
|
0.725 (0.507–1.037)
|
NS
|
Number of embryo transferred (2 versus 1)
|
1.359 (0.890–2.076)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
2.304 (1.586–3.347)
|
P < 0.001
|
Tubal factor (yes versus no)
|
1.111 (0.769–1.605)
|
NS
|
Ovulatory disorder (yes versus no)
|
0.929 (0.631–1.367)
|
NS
|
Male factor (yes versus no)
|
1.236 (0.854–1.790)
|
NS
|
Unexplained factor (yes versus no)
|
2.149 (0.910–5.075)
|
NS
|
Spontaneous abortion
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
1.350 (0.854–2.135)
|
NS
|
Age (35–37 versus ≤ 34)
|
1.190 (0.598–2.368)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.987 (0.279–3.490)
|
NS
|
BMI (< 18.5 versus 18.5–24.9)
|
1.267 (0.515–3.114)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
2.656 (1.660–4.250)
|
P < 0.001
|
Insemination method (ICSI versus IVF)
|
1.059 (0.559–2.004)
|
NS
|
Number of embryo transferred (2 versus 1)
|
0.799 (0.409–1.562)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
0.843 (0.466–1.526)
|
NS
|
Tubal factor (yes versus no)
|
0.443 (0.232–0.848)
|
P < 0.05
|
Ovulatory disorder (yes versus no)
|
0.856 (0.457–1.606)
|
NS
|
Male factor (yes versus no)
|
0.358 (0.178–0.723)
|
P < 0.01
|
Unexplained factor (yes versus no)
|
0.239 (0.049–1.167)
|
NS
|
Live birth
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
0.939 (0.723–1.220)
|
NS
|
Age (35–37 versus ≤ 34)
|
0.962 (0.630–1.468)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.423 (0.192–0.934)
|
P < 0.05
|
BMI (< 18.5 versus 18.5–24.9)
|
1.270 (0.747–2.161)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
0.853 (0.623–1.169)
|
NS
|
Insemination method (ICSI versus IVF)
|
0.794 (0.560–1.126)
|
NS
|
Number of embryo transferred (2 versus 1)
|
1.324 (0.893–1.961)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
2.270 (1.605–3.211)
|
P < 0.001
|
Tubal factor (yes versus no)
|
1.459 (1.071–2.092)
|
P < 0.05
|
Ovulatory disorder (yes versus no)
|
0.916 (0.629–1.334)
|
NS
|
Male factor (yes versus no)
|
1.588 (1.111–2.272)
|
P < 0.05
|
Unexplained factor (yes versus no)
|
2.973 (1.336–6.619)
|
P < 0.01
|
Abbreviations BMI, body mass index; FET, frozen embryo transfer; GnRH-a, gonadotrophin-releasing hormone agonist; IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection; OR, odds ratio; CI, confidence interval; NS, not significant.
aImmediate FET and bdelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards.
*Using the multivariable logistic regression and adjusting for maternal age, BMI, insemination method, number of embryo transferred, embryo stage and cause of infertility.
Table 6
Multivariable logistic regression analysis on risk factors for pregnancy outcomes in long-acting GnRH-a long protocol
Potential risk factor variables
|
Adjusted OR* (95% CI)
|
P-value
|
Clinical pregnancy
|
|
|
FET timing (Immediate FETa versus delayed FETb)
|
0.702 (0.382–1.292)
|
NS
|
Age (35–37 versus ≤ 34)
|
1.153 (0.461–2.883)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
0.706 (10.106–4.696)
|
NS
|
BMI (< 18.5 versus 18.5–24.9)
|
0.907 (0.272–3.020)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
1.243 (0.605–2.555)
|
NS
|
Insemination method (ICSI versus IVF)
|
1.306 (0.544–3.132)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
1.854 (0.944–3.643)
|
NS
|
Tubal factor (yes versus no)
|
2.545 (0.988–6.552)
|
P < 0.05
|
Ovulatory disorder (yes versus no)
|
0.732 (0.226–2.369)
|
NS
|
Male factor (yes versus no)
|
2.535 (1.058–6.070)
|
NS
|
Unexplained factor (yes versus no)
|
1.383 (0.239–7.999)
|
NS
|
Spontaneous abortion
|
Adjusted OR# (95% CI)
|
|
FET timing (Immediate FETa versus delayed FETb)
|
0.375 (0.142–0.990)
|
P < 0.05
|
Age (35–37 versus ≤ 34)
|
0.409 (0.089–1.887)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
-
|
NS
|
BMI (< 18.5 versus 18.5–24.9)
|
0.548 (0.066–4.518)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
1.959 (0.791–4.849)
|
NS
|
Live birth
|
Adjusted OR* (95% CI)
|
P-value
|
FET timing (Immediate FETa versus delayed FETb)
|
1.124 (0.625–2.023)
|
NS
|
Age (35–37 versus ≤ 34)
|
1.774 (0.730–4.311)
|
NS
|
Age (≥ 38 versus ≤ 34)
|
1.501 (0.221–10.185)
|
NS
|
BMI (< 18.5 versus 18.5–24.9)
|
1.134 (0.359–3.582)
|
NS
|
BMI (≥ 25 versus 18.5–24.9)
|
0.895 (0.454–1.764)
|
NS
|
Insemination method (ICSI versus IVF)
|
1.607 (0.712–3.631)
|
NS
|
Embryo stage (blastocyst versus cleavage)
|
1.798 (0.959–3.370)
|
NS
|
Tubal factor (yes versus no)
|
2.156 (0.922–5.042)
|
NS
|
Ovulatory disorder (yes versus no)
|
0.531 (0.159–1.769)
|
NS
|
Male factor (yes versus no)
|
1.379 (0.635–2.993)
|
NS
|
Unexplained factor (yes versus no)
|
0.474 (0.070–3.203)
|
NS
|
Abbreviations BMI, body mass index; FET, frozen embryo transfer; GnRH-a, gonadotrophin-releasing hormone agonist; IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection; OR, odds ratio; CI, confidence interval; NS, not significant.
aImmediate FET and bdelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards.
*Using the multivariable logistic regression and adjusting for maternal age, BMI, insemination method, trigger type, embryo stage and cause of infertility.
# Using the multivariable logistic regression and adjusting for maternal age, BMI.
"-" means that the number of miscarriages in the group over 38 years old is 0.