A total of 3,362 patients who met the inclusion criteria were included in the study from January 2016 to October 2018. A total of 22 pregnant patients were lost to follow-up in this study. The clinical and neonatal outcomes were analyzed according to age, using a cutoff of 35 years. The patients’ baseline characteristics are presented in Table 1. When patients were in the same age category, no significant differences were found in terms of age, body mass index (BMI), basal FSH, anti-mullerian hormone (AMH), infertility duration, type of infertility, type of endometrial preparation, and endometrium thickness (all values of P>0.05).
Table 1. Baseline characteristics of patients among groups A–E stratified by age
|
<35years of age
|
≥35years of age
|
|
Group A
|
Group B
|
Group C
|
Group D
|
Group E
|
P
|
Group A
|
Group B
|
Group C
|
Group D
|
Group E
|
P
|
Cycles (n)
|
1425
|
844
|
206
|
183
|
120
|
|
144
|
269
|
107
|
39
|
25
|
|
female age(year)
|
29.17±2.89
|
29.32±2.92
|
29.45±2.93
|
29.50±2.69
|
29.38±3.62
|
0.419
|
36.65±1.91
|
37.17±2.01
|
37.16±1.93
|
37.51±2.53
|
37.08±2.57
|
0.063
|
BMI (kg/m2)
|
21.46±3.09
|
21.70±3.20
|
21.34±3.13
|
21.71±3.48
|
21.67±3.41
|
0.343
|
21.96±2.75
|
22.59±2.82
|
22.59±2.88
|
22.38±2.45
|
22.06±2.41
|
0.210
|
Basal FSH (mIU/ml)
|
5.08±1.24
|
4.92±1.25
|
5.07±1.37
|
4.96±1.21
|
5.16±1.44
|
0.104
|
5.15±1.63
|
5.15±1.31
|
4.81±1.22
|
5.15±1.66
|
5.11±0.91
|
0.701
|
AMH (ng/ml)
|
8.06±5.71
|
7.80±4.03
|
7.22±3.68
|
6.85±3.72
|
6.98±3.80
|
0.095
|
6.08±3.56
|
6.34±3.75
|
5.08±2.25
|
5.74±3.86
|
5.80±3.07
|
0.347
|
Duration of infertility (years)
|
3.44±1.94
|
3.57±2.06
|
3.85±2.08
|
3.53±1.94
|
3.33±1.89
|
0.052
|
4.21±3.39
|
5.08±3.92
|
5.06±3.96
|
5.81±4.17
|
4.72±3.02
|
0.099
|
Type of infertility
|
|
|
|
|
|
0.276
|
|
|
|
|
|
0.522
|
Primary infertility
|
56.14
(800/1425)
|
52.25
(441/844)
|
56.31
(116/206)
|
55.19
(101/183)
|
60.83
(73/120)
|
|
27.08
(39/144)
|
33.09
(89/269)
|
25.23
(27/107)
|
33.33
(13/39)
|
28.0
(7/25)
|
|
Secondary infertility
|
43.86
(625/1425)
|
47.75
(403/844)
|
43.69
(90/206)
|
44.81
(82/183)
|
39.17
(47/120)
|
|
72.92
(105/144)
|
66.91
(180/269)
|
74.77
(80/107)
|
66.67
(26/39)
|
72.0
(18/25)
|
|
Endometrial preparation (%)
|
|
|
|
|
|
0.669
|
|
|
|
|
|
0.149
|
Natural
|
84.0
(1197/1425)
|
86.26
(728/844)
|
85.44
(176/206)
|
84.70
(155/183)
|
83.33
(100/120)
|
|
70.83
(102/144)
|
76.95
(207/269)
|
82.24
(88/107)
|
79.49
(31/39)
|
64.0
(16/25)
|
|
HRT
|
16.0
(228/1425)
|
13.74
(116/844)
|
14.56
(30/206)
|
15.30
(28/183)
|
16.67
(20/120)
|
|
29.17
(42/144)
|
23.05
(62/269)
|
17.76
(19/107)
|
20.51
(8/39)
|
36.0
(9/25)
|
|
Endometrial thickness (mm)
|
9.04±1.61
|
8.67±1.58
|
8.85±1.53
|
8.93±1.60
|
8.99±1.56
|
0.106
|
8.98±1.83
|
8.89±1.61
|
8.96±1.63
|
8.86±1.73
|
9.13±1.52
|
0.939
|
BMI, body mass index; FSH, follicle-stimulating hormone; AMH, anti-mullerian hormone; HRT, hormone replacement therapy
group A, one good-quality blastocyst; group B, two good-quality blastocysts; group C, one good- and one average-quality blastocyst; group D, two average-quality blastocysts
The clinical outcomes of the patients in groups A–D stratified by 35 years of age are shown in Table 2. There were significant differences in the rates of implantation, clinical pregnancy, live birth, and multiple pregnancy among groups A–D when patients were in the same age category. For women under 35 years old, the LBR in groups B and C was significantly higher than group A, but the LBR in group A was acceptable (54.2%), and the multiple pregnancy rate (MPR, 3.5%) was significantly lower than groups B (62.4%) and C (49.7%). There was no significant difference in the LBR between groups D and A, but the MPR in group D was significantly higher than that in group A (50% vs. 3.5%). In women 35 years of age and older, the LBR (which still reached 42.4%) and MPR (6.3% vs. 49.2%) in group A were significantly lower than that in group B. There was no significant difference in the LBR between groups A and C or D, but the MPR in group A was significantly lower than that in groups C and D. Meanwhile, we compared the clinical outcomes of patients with two average-quality blastocysts (group D) versus one average-quality blastocyst (group E). The results showed that for patients under 35 years old, the LBR in group D was higher than that in group E, but the MPR was as high as 50% (P < 0.01). In women 35 years of age and older, there was no significant difference in the LBR and MPR between groups D and E; however, patients in group D had a nonsignificant trend toward a higher multiple rate than group E (31.3% vs. 10%).
Table 2. The clinical outcomes of patients in groups A–D stratified by 35 years of age
|
<35years of age
|
≥35years of age
|
|
Group A
|
Group B
|
Group C
|
Group D
|
Group E
|
P#
|
Group A
|
Group B
|
Group C
|
Group D
|
Group E
|
P#
|
Cycles (n)
|
1425
|
844
|
206
|
183
|
120
|
|
144
|
269
|
107
|
39
|
25
|
|
Implantation rate
|
63.72b,c(908/1425)
|
60.37(1019/1688)
|
53.64(221/412)
|
45.90(168/366)
|
46.67(56/120)
|
0.000
|
55.56b,c(80/144)
|
52.97(285/538)
|
40.19(86/214)
|
26.92(21/78)
|
40.0(10/25)
|
0.000
|
Pregnancy rate
|
63.72a,b(908/1425)
|
75.59(638/844)
|
72.33(149/206)
|
62.30(114/183)
|
46.67d(56/120)
|
0.000
|
55.56a(80/144)
|
73.23(197/269)
|
57.0(61/107)
|
41.03(16/39)
|
40.0(10/25)
|
0.000
|
Live birth
|
54.25a,b(773/1425)
|
64.57
(545/844)
|
64.08
(132/206)
|
48.63
(89/183)
|
36.67 d(44/120)
|
0.000
|
42.36a(61/144)
|
59.48(160/269)
|
48.60(52/107)
|
30.77(12/39)
|
24.0(6/25)
|
0.000
|
Singleton
|
52.70a,b,c
(751/1425)
|
33.05(279/844)
|
38.84(80/206)
|
25.13(46/183)
|
36.67d
(44/120)
|
0.000
|
40.97
(59/144)
|
38.29(103/269)
|
33.64(36/107)
|
23.08(9/39)
|
24.0
(6/25)
|
0.177
|
Twin
|
1.55a,b,c
(22/1425)
|
31.52(266/844)
|
25.24(52/206)
|
23.50
(43/183)
|
0.0d
(0/120)
|
0.000
|
1.39a,b
(2/144)
|
21.19
(57/269)
|
14.95
(16/107)
|
7.69
(3/39)
|
0.0
(0/25)
|
0.000
|
Multiple pregnancy rate
|
3.52a,b,c
(32/908)
|
62.38
(398/638)
|
49.66
(74/149)
|
50.0
(57/114)
|
0.0d
(0/56)
|
0.000
|
6.25a,b,c
(5/80)
|
49.24
(97/197)
|
42.62
(26/61)
|
31.25
(5/16)
|
10.0
(1/10)
|
0.000
|
Monozygotic twins rate
|
3.52
(32/908)
|
2.66
(17/638)
|
1.34
(2/149)
|
2.63
(3/114)
|
0.0
(0/56)
|
0.462
|
6.25
(5/80)
|
4.57
(9/197)
|
1.64
(1/61)
|
0.0
(0/16)
|
10.0
(1/10)
|
0.462
|
Early abortion rate
|
11.67a
(106/908)
|
8.31
(53/638)
|
8.72
(13/149)
|
15.79
(18/114)
|
21.43
(12/56)
|
0.037
|
20.0
(16/80)
|
17.26
(34/197)
|
13.11
(8/61)
|
18.75
(3/16)
|
27.27
(3/11)
|
0.758
|
Abortion rate
|
13.33
(121/908)
|
11.44
(73/638)
|
9.40
(14/149)
|
19.30
(22/114)
|
21.43
(12/56)
|
0.067
|
21.25
(17/80)
|
18.78
(37/197)
|
14.75
(9/61)
|
25.0
(4/16)
|
27.27
(3/11)
|
0.715
|
Ectopic pregnancy rate
|
0.88
(8/908)
|
1.25
(8/638)
|
1.34
(2/149)
|
0.0
(0/114)
|
0.0
(0/56)
|
0.597
|
2.50
(2/80)
|
0.0
(0/197)
|
0.0
(0/61)
|
0.0
(0/16)
|
10.0
(1/10)
|
0.076
|
#comparison among groups A–D. P < 0.05 was considered statistically significant
a P < .05 compared to group B
b P < .05 compared to group C
c P < .05 compared to group D
d P < .05 between groups D and E
Comparisons of neonatal outcomes of patients among groups A–E stratified by 35 years of age are presented in Table 3. The results showed that 70–90% of preterm births resulted from multiple pregnancies, and about 85–95% of low birth weight babies come from multiple pregnancies. When patients were in the same age category, the gestational age, birth weight, and birth height of group A were significantly higher than those in groups B, C, or D, but this statistical difference disappeared if the patients were subgrouped by singleton or twin birth. Meanwhile, there was no significant difference in terms of the gestational age, birth weight, and birth height between groups A and E. Finally, the neonatal outcomes were compared between groups D and E, and the results showed that the gestational age, birth weight, and birth height of patients in group D were significantly lower than those in group E when patients were in the same age category.
Table 3. The neonatal outcomes of patients among groups A–E stratified by 35 years of age
|
<35years of age
|
≥35years of age
|
|
Group A
|
Group B
|
Group C
|
Group D
|
Group E
|
P
|
Group A
|
Group B
|
Group C
|
Group D
|
Group E
|
P
|
Cycles (n)
|
1425
|
844
|
206
|
183
|
120
|
|
144
|
269
|
107
|
39
|
25
|
|
Preterm birth
(<37weeks)
|
11.77a,b,c
(91/773)
|
39.45
(215/545)
|
33.33
(44/132)
|
42.70
(38/89)
|
4.55d
(2/44)
|
0.000
|
8.20a,b
(5/61)
|
35.0
(56/160)
|
25.0
(13/52)
|
16.67
(2/12)
|
16.67
(1/6)
|
0.001
|
Singleton
|
8.67a
(67/773)
|
3.30
(18/545)
|
6.82
(9/132)
|
3.37
(3/89)
|
4.55
(2/44)
|
0.001
|
4.92
(3/61)
|
5.62
(9/160)
|
7.69
(4/52)
|
0.0
(0/12)
|
0.0
(0/6)
|
0.755
|
Twin
|
3.10a,b,c
(24/773)
|
36.15
(197/545)
|
26.51
(35/132)
|
39.33
(35/89)
|
0.0d
(0/44)
|
0.000
|
3.28a,b
(2/61)
|
29.38
(47/160)
|
17.31
(9/52)
|
16.67
(2/12)
|
16.67
(1/6)
|
0.000
|
Gestational age (weeks)
|
38.70±1.94a,b,c
|
37.37±2.52
|
37.59±2.52
|
36.86±3.33
|
39.18±1.91d
|
0.000
|
38.72±1.23a,b,c
|
37.61±2.33
|
37.66±2.89
|
37.00±3.43
|
38.32±0.86d
|
0.022
|
Singleton
|
38.80±1.83
|
38.94±1.71
|
38.51±2.18
|
39.00±1.58
|
39.18±1.91
|
0.325
|
38.81±1.56
|
38.59±2.14
|
38.76±1.97
|
38.52±1.71
|
38.32±0.86
|
0.951
|
Twin
|
35.32±1.47
|
36.04±2.32
|
36.02±2.37
|
35.15±3.01
|
/
|
0.095#
|
36.20±0.40
|
35.98±1.63
|
35.06±3.21
|
34.29±4.99
|
/
|
0.330#
|
Birth height (mm)
|
49.51±2.3a,b,c
|
47.72±3.21
|
48.23±2.41
|
46.61±4.26
|
49.89±2.22d
|
0.000
|
49.77±1.85a,b,c
|
48.03±2.70
|
47.95±3.75
|
48.31±5.70
|
49.75±0.96d
|
0.000
|
Singleton
|
49.68±2.27
|
49.82±1.98
|
49.88±1.73
|
49.53±1.44
|
49.88±2.22
|
0.838
|
49.93±1.76
|
49.50±2.39
|
49.77±2.41
|
50.00±2.00
|
49.75±0.96
|
0.868
|
Twin
|
46.66±2.40
|
46.72±2.95
|
46.97±2.20
|
45.50±4.32
|
/
|
0.113#
|
46.75±0.35
|
46.90±1.91
|
45.70±3.70
|
45.83±6.83
|
/
|
0.155#
|
Birth weight (kg)
|
3.16±.054a,b,c
|
2.73±0.61
|
2.79±0.62
|
2.57±0.66
|
3.19±0.43d
|
0.000
|
3.12±0.51a,b,c
|
2.76±0.60
|
2.81±0.75
|
2.55±0.88
|
3.30±0.29d
|
0.000
|
Singleton
|
3.22±0.50
|
3.27±0.51
|
3.24±0.52
|
3.17±0.33
|
3.19±0.43
|
0.583
|
3.36±0.49
|
3.22±0.50
|
3.24±0.49
|
3.26±0.45
|
3.30±0.29
|
0.666
|
Twin
|
2.34±0.43
|
2.48±0.45
|
2.44±0.42
|
2.31±0.54
|
/
|
0.113#
|
2.55±0.25
|
2.43±0.34
|
2.24±0.52
|
2.00±0.82
|
/
|
0.142#
|
Still birth
|
0.0
(0/773)
|
0.0
(0/545)
|
0.0
(0/132)
|
0.0
(0/89)
|
0.0
(0/44)
|
/
|
0.0
(0/61)
|
0.0
(0/160)
|
0.0
(0/52)
|
0.0
(0/12)
|
0.0
(0/6)
|
/
|
Congenital anomalies
|
1.64
(13/795)
|
1.60
(13/811)
|
1.09
(2/184)
|
1.52
(2/132)
|
2.27
(1/44)
|
0.958
|
0.0
(0/63)
|
0.0
(0/217)
|
0.0
(0/68)
|
0.0
(0/15)
|
0.0
(0/6)
|
/
|
Sex ratio(male/female)
|
1.30
(450/345)
|
1.43
(477/334)
|
1.10
(97/87)
|
1.46
(78/54)
|
0.83
(20/24)
|
0.445
|
1.43
(37/26)
|
1.22
(119/98)
|
1.16
(37/31)
|
0.63
(6/9))
|
1.00
(3/3)
|
0.632
|
Low birth weight
(<2500 g) in singleton
|
7.04a,b,c
(56/795)
|
27.25
(221/811)
|
28.26
(52/184)
|
34.09
(45/132)
|
4.55d
(2/44)
|
0.000
|
6.34a,b
(4/63)
|
29.03
(63/217)
|
27.94
(19/68)
|
13.33
(2/15)
|
0.0
(0/6)
|
0.002
|
Singleton
|
4.02
(32/795)
|
4.44
(36/811)
|
4.35
(8/184)
|
4.55
(6/132)
|
4.55
(2/44)
|
0.977
|
3.17
(2/63)
|
2.76
(6/217)
|
1.47
(1/68)
|
0.0
(0/1)
|
0.0
(0/6)
|
0.833
|
Twin
|
3.02a,b,c
(24/795)
|
22.81
(185/811)
|
23.91
(44/184)
|
29.54
(39/132)
|
0.0d
(0/44)
|
0.000
|
3.17a,b
(2/63)
|
26.27
(57/217)
|
26.47
(18/68)
|
13.33
(2/15)
|
0.0
(0/6)
|
0.001
|
Very low birth weight(<1500 g) in singleton
|
0.75a,c
(6/795)
|
2.84
(23/811)
|
1.63
(3/184)
|
5.30
(7/132)
|
0.0
(0/44)
|
0.001
|
0.0c
(0/63)
|
2.76
(6/217)
|
2.94
(2/68)
|
13.33
(2/15)
|
0.0
(0/6)
|
0.045
|
Singleton
|
0.63
(5/795)
|
0.12
(1/811)
|
0.54
(1/184)
|
0.0
(0/132)
|
0.0
(0/44)
|
0.324
|
0.0
(0/63)
|
0.5
(1/217)
|
0.0
(0/68)
|
0.0
(0/15)
|
0.0
(0/6)
|
0.879
|
Twin
|
0.12a,c
(1/795)
|
2.72
(22/811)
|
1.09
(2/184)
|
5.30
(7/13)
|
0.0
(0/44)
|
0.000
|
0.0c
(0/63)
|
2.30
(5/217)
|
2.94
(2/68)
|
13.33
(2/15)
|
0.0
(0/6)
|
0.029
|
#comparison among groups A–D. P < 0.05 was considered statistically significant
a P < .05 compared to group B
b P < .05 compared to group C
c P < .05 compared to group D
d P < .05 between groups D and E