Table 1 Baseline characteristics of the study population before and after PSM.

Maternal age at embryo transfer (years; mean (SD))

30.65 ± 4.23

30.42 ± 4.17

0.124

30.60 ± 4.22

30.61 ± 4.10

0.983

0.001

Maternal BMI (kg/m2; mean (SD))

21.79 ± 2.55

22.12 ± 2.34

< 0.001

21.81 ± 2.55

21.83 ± 2.28

0.828

0.009

Education, n (%)

0.002

0.227

0.069

Primary school and below

42(4.80%)

611(5.70%)

42 (4.88%)

182 (5.43%)

Secondary and High Schools

485(55.50%) ^a

6509(60.50%)

479 (55.70%)

1961 (58.47%)

College and above

347(39.70%) ^a

3631(33.80%)

339 (39.42%)

1221 (36.10%)

Family residence, n (%)

0.023

0.127

0.077

Changsha city

91(10.40%) ^a

861(8.00%)

90 (10.47%)

292 (8.70%)

Outside Changsha and within Hunan Province

520(59.50%)

6361(59.20%)

512 (59.53%)

1962 (58.50%)

Outside Hunan Province

263(30.10%)

3529(32.80%)

258 (30.00%)

1100 (32.80%)

Occupational status, n (%)

0.010

0.287

0.075

Employed

357(40.80%) ^a

3907(36.30%)

352 (40.93%)

1290 (38.46%)

Self-employed

100(11.40%) ^a

1601(14.90%)

99 (11.51%)

459 (13.69%)

Freelance

126(14.40%)

1626(15.10%)

126 (14.65%)

515 (15.35%)

Housewife

291(33.30%)

3617(33.60%)

283 (32.91%)

1090 (32.50%)

Occupational exposure, n (%)

0.937

0.595

0.020

‘Unexposed’ occupation

808(92.40%)

9947(92.50%)

794 (92.33%)

3078 (91.77%)

‘Exposed’ occupation

66(7.60%)

804(7.50%)

66 (7.67%)

276 (8.23%)

Duration of infertility (years; median (interquartile range))

3.71 ± 2.85

4.02 ± 3.05

0.005

3.73 ± 2.86

3.76 ± 2.91

0.737

0.013

Type of infertility, n(%)

0.839

0.734

0.013

Primary infertility

411(47.0%)

5094(47.40%)

403 (46.86%)

1550 (46.21%)

Secondary infertility

463(53.0%)

5657(52.60%)

457 (53.14%)

1804 (53.79%)

Gravidity (n; median (interquartile range))

1(0,2)

1(0,2)

0.816

1 (0,2)

1 (0,2)

0.287

0.054

Parity (n; median (interquartile range))

0(0,0)

0(0,0)

0.375

0 (0,0)

0 (0,0)

0.170

0.045

Main indication for ART, n(%)

0.001

0.652

0.078

Tubal factor

561(64.20%) ^a

7259(67.50%)

557 (64.77%)

2184 (65.12%)

Ovulation disorders

78(8.90%)

963(9.00%)

78 (9.07%)

322 (9.60%)

Endometriosis

48(5.50%)

457(4.30%)

46 (5.35%)

178 (5.31%)

DOR

32(3.70%)

378(3.50%)

32 (3.72%)

128 (3.82%)

Male factor

117(13.40%)

1415(13.20%)

114 (13.26%)

422 (12.58%)

RSA

10(1.10%)

84(0.80%)

3 (0.35%)

1 (0.03%)

Chromosomal abnormality

20(2.30%)

174(1.60%)

10 (1.16%)

38 (1.13%)

Unexplained infertility

8(0.90%) ^a

21(0.20%)

20 (2.33%)

81 (2.42%)

AMH, ng/ml; median (IQR)

3.43(2.11,5.48)

3.54(2.00,5.81)

0.231

3.34 (1.94,5.37)

3.64 (2.07,6.07)

0.309

0.104

Basal FSH, mIU/ml; median (IQR)

6.21(5.20,7.50)

6.30(5.30,7.50)

0.378

6.30 (5.30,7.72)

6.36 (5.28,7.55)

0.338

0.045

Basal LH, mIU/ml; median (IQR)

4.80(3.60,6.30)

4.90(3.53,6.61)

0.220

4.79 (3.69,6.40)

5.11 (3.70,7.00)

0.168

0.097

Basal estradiol, pg/ml; median (IQR)

34.51(26.17,45.26)

34.00(25.00,44.40)

0.112

35.68 (27.00,47.55)

35.17 (26.53,45.48)

0.247

0.042

Testosterone, ng/mL; median (IQR)

0.25(0.16,0.34)

0.24(0.16,0.33)

0.523

0.26 (0.17,0.35)

0.25 (0.17,0.35)

0.576

0.025

AFC, n (%)

0.118

0.247

0.079

1–6

83(9.50%)

1220(11.30%)

81 (9.42%)

378 (11.27%)

7–12

257(29.40%)

3386(31.50%)

251 (29.19%)

1015 (30.26%)

13–24

513(58.70%) ^a

5918(55.00%)

507 (58.95%)

1866 (55.64%)

> 24

21(2.40%)

227(2.10%)

21 (2.44%)

95 (2.83%)

Thyroid-stimulating hormone, uIU/ml; median (IQR)

2.17(1.50,3.07)

2.17(1.51,3.06)

0.737

2.11 (1.48,2.96)

2.24 (1.55,3.06)

0.825

0.006

Serum triglyceride (mmol/L; median (IQR))

0.99(0.75,1.46)

1.06(0.78,1.48)

0.291

1.04 (0.79,1.53)

1.08 (0.81,1.47)

0.051

0.029

Total cholesterol (mmol/L; median (IQR))

4.61(4.12,5.13)

4.62(4.11,5.19)

0.922

4.59 (4.10,5.11)

4.66 (4.11,5.20)

0.692

0.010

Low-density lipoprotein cholesterol (mmol/L; median (IQR))

2.74(2.31,3.16)

2.71(2.29,3.19)

0.835

2.76 (2.34,3.17)

2.76 (2.33,3.21)

0.609

0.009

High-density lipoprotein cholesterol (mmol/L; median (IQR))

1.40(1.20,1.65)

1.41(1.21,1.64)

0.376

1.34 (1.15,1.59)

1.40 (1.21,1.61)

0.139

0.071

Dyslipidemia, (%, n)

38.20% (247/646)

39.40% (3082/7815)

0.548

38.60% (245/635)

38.70% (930/2401)

0.945

0.003

Fasting blood glucose (mmol/L; median (IQR))

5.27(5.00,5.56)

5.29(5.03,5.56)

0.128

5.23 (4.94,5.53)

5.26 (5.01,5.55)

0.390

0.045

Fasting insulin (uU/mL; median (IQR))

9.00(6.55,12.90)

9.58(6.92,13.18)

0.007

8.98 (6.39,13.36)

9.34 (6.73,13.03)

0.381

0.028

HOMA-IR, % (n/N)

0.051

0.651

0.020

< 2.5

62.70% (399/636)

58.80% (4588/7806)

62.52% (392/627)

61.50% (1470/2389)

≥ 2.5

37.30% (237/636)

41.20% (3218/7806)

37.48% (235/627)

38.50% (919/2389)

Type of cycle, % (n/N)

< 0.001

0.357

0.035

Cycle with fresh embryo transfer

61.9% (541/874)

72.4% (7786/10751)

62.44% (537/860)

64.13% (2151/3354)

Cycle with frozen-thawed embryo transfer

38.1% (333/874)

27.6% (2965/10751)

37.56% (323/860)

35.87% (1203/3354)

Fertilization method, n (%)

0.278

0.466

0.048

IVF

636(72.80%)

7842(72.90%)

628 (73.02%)

2431 (72.48%)

ICSI

187(21.40%)

2149(12.00%)

182 (21.16%)

689 (20.54%)

IVF + ICSI

51(5.80%)

760(7.10%)

50 (5.81%)

234 (6.98%)

Endometrial thickness (mm; mean (SD))

10.47 ± 2.18

10.59 ± 2.14

0.126

10.48 ± 2.19

10.47 ± 2.15

0.947

0.005

Endometrial type, n (%)

0.011

0.706

0.032

A

323(37.00%) ^a

4527(42.10%)

322 (37.44%)

1276 (38.04%)

B

483(55.30%) ^a

5496(51.10%)

474 (55.12%)

1805 (53.82%)

C

68(7.80%)

728(6.80%)

64 (7.44%)

273 (8.14%)

Stage of embryo development, n (%)

< 0.001

0.816

0.028

Cleavage stage embryos

1313 (86.73%)

17,633 (91.27%)

1305 (87.23%)

5116 (87.01%)

Blastocyst stage embryos

201 (13.27%)

1686 (8.73%)

191 (12.17%)

764 (12.99%)

No. of embryos transferred (n; mean (SD))

1.73 ± 0.44

1.80 ± 0.40

< 0.001

1.74 ± 0.44

1.75 ± 0.43

0.411

0.031

Good-quality embryos transferred rate, % (n/N)

88.84% (1345/1514)

92.10% (17793/19319)

< 0.001

89.30% (1336/1496)

89.54% (5265/5880)

0.790

0.029

Clinician’ title, n (%)

0.057

0.832

0.008

Associate chief physician and above

692(79.20%)

8791(81.80%)

688 (80.00%)

2694 (80.32%)

Attending physician

182(20.80%)

1960(18.20%)

172 (20.00%)

660 (19.68%)

Clinician’ gender, n (%)

0.080

0.658

0.017

Female

614(70.30%)

7847(73.00%)

607 (70.58%)

2393 (71.35%)

Male

260(29.70%)

2904(27.00%)

253 (29.42%)

961 (28.65%)