Table 1 Maternal and cycle characteristics among the different groups

Number of transfer cycles

939

1224

1598

—

Female age (years)

31.5±4.4

31.4±4.4

31.1±4.5

0.064

Female BMI (kg/m²)

22.7±3.3

22.4±3.3

22.7±3.3

0.084

Duration of infertility (years)

3.7±2.8

3.6±2.7

3.5±2.7

0.317

Pattern of infertility

 Primary

473(50.4)^a

558(45.6)

791(49.5)

0.047

 Secondary

466(49.6)

666(54.4)

807(50.5)

—

Endometrial preparation

 HRT cycles

774(82.4)

1022(83.5)

1345(84.2)

0.518

 Mild stimulation cycles

31(3.3)

26(2.1)

56(3.5)

0.078

 Gn stimulation cycles

24(2.6)

29(2.4)

43(2.7)

0.865

 Natural cycles

6(0.6)

15(1.2)

17(1.1)

0.378

 Modified natural cycles

104(11.1)

132(10.8)

137(8.6)

0.055

 Thickness of endometrium (mm)

9.6±1.6

9.5±1.6

9.6±1.7

0.359

Pattern of insemination

 IVF

706(75.2)^b

926(75.7)^b

1370(85.7)^c

<0.001

 ICSI

233(24.8)

298(24.3)

228(14.3)

—

Evenness of the blastomeres of day 3 embryo

 Even

654(69.6)^b

1001(81.8)^c

1191(74.5)^d

<0.001

 Uneven

285(30.4)

223(18.2)

407(25.5)

—

Fragmentation of day 3 embryo

 <10%

471(50.2)^b

780(63.7)^c

1183(74.0)^d

<0.001

 10-25%

441(47.0)^b

439(35.9)^c

411(25.7)^d

<0.001

 >25%

27(2.9)^b

5(0.4)^c

4(0.3)^c

<0.001

Grade of transferred blastocysts

 Good quality

143(15.2)^b

379(31.0)^c

598(37.4)^d

<0.001

 Fair quality

487(51.9)^b

629(51.4)^b

746(46.7)^c

0.012

 Poor quality

309(32.9)^b

216(17.6)^c

254(15.9)^c

<0.001

Previous transfer cycles

 0

336(35.8)^b

561(45.8)^c

739(46.2)^c

<0.001

 1

428(45.6)^b

468(38.2)^c

632(39.5)^c

0.001

 2

115(12.2)

130(10.6)

162(10.1)

0.250

 ≥3

60(6.4)^b

65(5.3)^b,c

65(4.1)^c

0.031