As shown in Table 1, female age, proportion of primary infertility, basal FSH, rFSH starting dose and rFSH total dose were significantly lower in the SBT group than those in the DET group, and AMH concentration, AFC, number of retrieved oocytes, proportion of IVF, number of 2PN zygotes and number of usable embryos were significantly higher in the SBT group than those in the DET group. There were no significant differences in female BMI, duration of infertility, basal LH, ovarian stimulation type or thickness of endometrium between the two groups.
Table 1. Maternal and cycle characteristics between the two groups. BMI body mass index, FSH follicle-stimulating hormone, LH luteinizing hormone, AMH anti-Müllerian hormone, rFSH recombinant follicle-stimulating hormone, GnRH gonadotrophin-releasing hormone, Gn gonadotropin, IVF in vitro fertilization, ICSI intracytoplasmic sperm injection.
|
SBT
|
DET
|
P value
|
Number of transfer cycles, n
|
1548
|
1393
|
—
|
Female age (years)
|
30.2±3.6
|
30.5±4.1
|
0.043
|
Female BMI (kg/m2)
|
23.0±3.3
|
23.3±3.2
|
0.065
|
Duration of infertility (years)
|
3.3±2.3
|
3.3±2.4
|
0.508
|
Pattern of infertility
|
|
|
|
Primary, n (%)
|
785(50.7)
|
808(58.0)
|
<0.001
|
Secondary, n (%)
|
763(49.3)
|
585(42.0)
|
<0.001
|
Basal FSH (IU/L)
|
6.6±1.6
|
6.9±1.8
|
<0.001
|
Basal LH (IU/L)
|
6.1±4.8
|
5.9±3.3
|
0.319
|
AMH (ng/mL)
|
4.0±2.2
|
3.5±2.1
|
<0.001
|
Antral follicle counts
|
21.5±11.7
|
18.4±7.6
|
<0.001
|
rFSH starting dose (IU/L)
|
134.7±45.0
|
163.6±68.3
|
<0.001
|
rFSH total dose (IU/L)
|
1976.1±657.8
|
2140.2±664.7
|
<0.001
|
Ovarian stimulation type
|
|
|
|
Long GnRH agonist protocol, n (%)
|
1489(96.2)
|
1322(94.9)
|
0.106
|
Prolonged GnRH agonist protocol, n (%)
|
55(3.6)
|
57(4.1)
|
0.500
|
GnRH antagonist protocol, n (%)
|
—
|
11(0.8)
|
—
|
Gn protocol, n (%)
|
4(0.3)
|
3(0.2)
|
1.000
|
Number of retrieved oocytes
|
12.7±3.9
|
11.0±3.8
|
<0.001
|
Pattern of insemination
|
|
|
|
IVF, n (%)
|
1285(83.0)
|
1037(74.4)
|
<0.001
|
ICSI, n (%)
|
263(17.0)
|
356(25.6)
|
<0.001
|
Number of 2PN zygotes
|
10.1±3.3
|
8.3±3.2
|
<0.001
|
Number of usable embryos
|
6.7±2.4
|
5.3±2.0
|
<0.001
|
Thickness of endometrium (mm)
|
12.1±2.6
|
12.0±2.6
|
0.195
|
Average number of transferred embryos, n
|
1
|
2
|
—
|
The grades of the transferred embryos or blastocysts in the two groups are shown in Table 2. In the SBT group, the proportion of fully expanded (IV+V) blastocysts in the transferred blastocysts reached 98.7% according to the degree of blastocyst expansion. The proportion of good-quality and fair-quality blastocysts according to the grades of the ICM and TE reached 35.1% and 60.3%, respectively. In the DET group, the proportion of transferred embryos with 8 or more cells reached 97.6%. The proportion of transferred embryos with uniform blastomeres reached 89.0%. The proportion of transferred embryos with less than 10% fragmentation reached 83.0%. Therefore, more than 80% of the transferred embryos in the DET group were good-quality embryos.
Table 2. Grades of transferred embryos or blastocysts in the two groups
|
SBT
|
DET
|
Number of transferred embryos, n
|
1548
|
2786
|
Day 3 embryo grade
|
—
|
|
Embryo cell number
|
—
|
|
<8cell, n (%)
|
—
|
69(2.5)
|
8cell, n (%)
|
—
|
1796(64.5)
|
>8cell, n (%)
|
—
|
921(33.1)
|
Blastomere uniformity
|
—
|
|
Even, n (%)
|
—
|
2480(89.0)
|
Uneven, n (%)
|
—
|
306(11.0)
|
Embryo fragmentation
|
—
|
|
<10%, n (%)
|
—
|
2313(83.0)
|
10-25%, n (%)
|
—
|
473(17.0)
|
Blastocysts grade
|
|
—
|
Expansion grade
|
|
—
|
Ⅲ, n (%)
|
20(1.3)
|
—
|
Ⅳ, n (%)
|
1501(97.0)
|
—
|
Ⅴ, n (%)
|
27(1.7)
|
—
|
Good quality (Ⅳ-ⅤAA/Ⅳ-ⅤAB/Ⅳ-ⅤBA), n (%)
|
544(35.1)
|
—
|
Fair quality (Ⅲ-ⅤBB), n (%)
|
933(60.3)
|
—
|
Poor quality (Ⅲ-ⅣAC/Ⅲ-ⅣBC/Ⅲ-ⅣCA/Ⅲ-ⅣCB), n (%)
|
71(4.6)
|
—
|
The clinical outcomes of the two groups are shown in Table 3. The rates of clinical pregnancy and live birth in the DET group were significantly higher than those in the SBT group (75.1% vs. 71.3%, P=0.020; 66.6% vs. 63.0%, P=0.041). The rate of twin pregnancy in the SBT group was significantly lower than that in the DET group (2.3% vs. 37.0%, P<0.001). The rates of ectopic pregnancy, miscarriage, termination of pregnancy and ongoing pregnancy were not significantly different between the two groups.
Table 3. Clinical outcomes in the two groups.
|
SBT
|
DET
|
P value
|
Number of transfer cycles, n
|
1548
|
1393
|
—
|
Number of clinical pregnancy cycles, n (%)
|
1103(71.3)a
|
1046(75.1)
|
0.020
|
Number of twin pregnancy cycles, n (%)
|
36(2.3)
|
516(37.0)
|
<0.001
|
Number of ectopic pregnancy cycles, n (%)
|
5(0.5)
|
10(1.0)
|
0.199
|
Number of miscarriage cycles, n (%)
|
115(10.4)
|
96(9.2)
|
0.346
|
Number of termination of pregnancy cycles, n (%)
|
8(0.7)
|
11(1.1)
|
0.493
|
Number of ongoing pregnancy cycles, n (%)
|
975(88.4)
|
929(88.8)
|
0.786
|
Number of live birth cycles (per transfer cycle), n (%)
|
975(63.0)
|
928(66.6)
|
0.041
|
The results of the logistic regression analysis of clinical pregnancy, twin pregnancy and live birth rates after adjustments for confounding factors according to the maternal and cycle characteristics are shown in Table 4. Female age, number of transferred embryos, ovarian stimulation type, number of 2PN zygotes and number of usable embryos were significant factors affecting clinical pregnancy rate. Female age, number of transferred embryos, basal LH, AFC and number of usable embryos were significant factors affecting twin pregnancy rate. Female age, number of transferred embryos, rFSH starting dose, ovarian stimulation type and endometrial thickness were significant factors affecting live birth rate. Among these significant factors, female age and the number of transferred embryos simultaneously affected the rates of clinical pregnancy, twin pregnancy and live birth.
Table 4. Results of the logistic regression analysis of clinical pregnancy, twin pregnancy and live birth rates after adjustments for confounding factors according to the maternal and cycle characteristics. PN pronuclei, LH luteinizing hormone, rFSH recombinant follicle-stimulating hormone.
|
Adjusted OR
|
95% CI
|
P value
|
Clinical pregnancy
|
|
|
|
Female age
|
0.953
|
0.930-0.977
|
<0.001
|
Number of transferred embryos
|
1.542
|
1.277-1.863
|
<0.001
|
Ovarian stimulation type
|
0.634
|
0.460-0.874
|
0.005
|
Number of 2PN zygotes
|
0.942
|
0.890-0.998
|
0.042
|
Number of usable embryos
|
1.108
|
1.049-1.171
|
<0.001
|
|
|
|
|
Twin pregnancy
|
|
|
|
Female age
|
0.927
|
0.898-0.957
|
<0.001
|
Number of transferred embryos
|
30.655
|
21.165-44.401
|
<0.001
|
Basal LH
|
1.025
|
1.001-1.050
|
0.038
|
Antral follicle counts
|
0.978
|
0.957-0.999
|
0.038
|
Number of usable embryos
|
1.095
|
1.021-1.175
|
0.012
|
|
|
|
|
Live birth
|
|
|
|
Female age
|
0.948
|
0.927-0.970
|
<0.001
|
Number of transferred embryos
|
1.431
|
1.202-1.704
|
<0.001
|
rFSH starting dose
|
0.997
|
0.996-0.999
|
0.001
|
Ovarian stimulation type
|
0.685
|
0.498-0.942
|
0.020
|
Thickness of endometrium
|
1.046
|
1.012-1.081
|
0.007
|
The impact of the number of transferred embryos on clinical pregnancy, twin pregnancy and live birth rates by age stratification are shown in Table 5. For females aged less than 35 years, the rates of clinical pregnancy and live birth in the DET group were significantly higher than those in the SBT group (adjusted OR (aOR) 1.792, 95% CI 1.455-2.207; aOR 1.572, 95% CI 1.301-1.901). For females aged 35 years and over, the rates of clinical pregnancy and live birth in the DET group were not significantly different compared with those in the SBT group (aOR 0.879, 95% CI 0.530-1.457; aOR 1.004, 95% CI 0.614-1.643). The twin pregnancy rate in the SBT group was significantly lower than that in the DET group at all ages (aOR 32.502, 95% CI 21.885-48.269; aOR 23.504, 95% CI 7.714-71.608).
Table 5. The impact of the number of transferred embryos on clinical pregnancy, twin pregnancy and live birth rates by age stratification.
|
Adjusted OR
|
95% CI
|
P value
|
< 35
|
|
|
|
Clinical pregnancy
|
1.792
|
1.455-2.207
|
<0.001
|
Twin pregnancy
|
32.502
|
21.885-48.269
|
<0.001
|
Live birth
|
1.572
|
1.301-1.901
|
<0.001
|
≥ 35
|
|
|
|
Clinical pregnancy
|
0.879
|
0.530-1.457
|
0.617
|
Twin pregnancy
|
23.504
|
7.714-71.608
|
<0.001
|
Live birth
|
1.004
|
0.614-1.643
|
0.986
|