Table 1 Ectopic pregnancy rate in fresh embryo transfer cycles and in frozen-thawed embryo transfer cycles

Total No.

27,600

672

2.43%

14,762

417

2.82%

Age (year)

 < 35

22,914

557

2.43%

0.925

12,064

342

2.83%

0.876

 ≥ 35

4686

115

2.45%

2698

75

2.78%

BMI (kg/m²)

 < 18.5

1703

56

3.29%

883

24

2.72%

 18.5–23.9

16,840

386

2.29%

0.029

8840

244

2.76%

0.782

 ≥ 24

9057

230

2.54%

5039

149

2.96%

Infertility type

 Primary

15,265

343

2.25%

0.024

6779

173

2.56%

0.065

 Secondary

12,335

329

2.67%

7983

244

3.06%

Tubal factor existed

 Yes

11,075

402

3.63%

< 0.001

5902

207

3.51%

< 0.001

 No

16,525

270

1.63%

8860

210

2.37%

Ovarian stimulation protocol

 Agonist

27,045

658

2.43%

/

 Antagonist

250

5

2.00%

0.763

/

 Others^*

305

9

2.95%

/

Peak Estrogen level (pg/ml)

 < 2500

9806

216

2.20%

/

 [2500–5000)

12,092

286

2.37%

0.011

/

 [5000–7500)

4104

116

2.83%

/

 ≥ 7500

1598

54

3.38%

/

Endometrial preparation Protocol

 Natural cycle

/

5204

133

2.56%

0.145

 Artificial cycle

/

9558

284

2.97%

Endometrial thickness (mm)⁺

 Thin (< 7)

385

21

5.45%

357

23

6.44%

 Medium (8–13)

17,901

480

2.68%

< 0.001

7624

238

3.12%

< 0.001

 Thick (≥ 14)

8420

147

1.75%

607

9

1.48%

Type of embryos

 Cleavage

22,222

582

2.62%

< 0.001

6503

241

3.71%

< 0.001

 Blastocyst

5378

90

1.67%

8259

176

2.13%

No. of embryos transferred

 1

6793

125

1.84%

6343

139

2.19%

 2

20,328

537

2.64%

0.001

7448

229

3.07%

< 0.001

 3

479

10

2.09%

971

49

5.05%