Table 4 Results of multiple regression analysis of singleton birthweight

(Constant)

− 3953.883

118.402

− 33.394

Paternal age (year)

1.224

1.154

0.014

1.060

Paternal education

 Below high school

− 23.543

16.245

− 0.018

− 1.449

 High school (reference)

 College

− 16.949

13.792

− 0.017

− 1.229

 Above college

− 40.042

21.485

− 0.023

− 1.864

Maternal age (year)

− 1.714

1.524

− 0.015

− 1.125

Maternal BMI (kg/m²)

24.929

1.562

0.135

15.959

Maternal education

 Below high school

− 13.133

15.866

− 0.011

− 0.828

 High school (reference)

 College

− 9.940

13.791

− 0.010

− 0.721

 Above college

− 6.272

23.371

− 0.003

− 0.268

Infertility cause

 Female (reference)

 Male

− 16.308

14.775

− 0.011

− 1.104

 Mixed

− 11.251

12.576

− 0.008

− 0.895

 Unexplained

33.220

26.724

0.011

1.243

Infertility duration (years)

0.149

1.528

0.001

0.098

Parity, high order (versus 0)

44.461

15.988

0.025

2.781

FET cycle rank, high order (versus first)

19.885

8.380

0.021

2.373

FET endometrial preparation, artificial cycle (versus natural cycle)

− 15.151

9.444

− 0.013

− 1.604

Endometrial thickness (mm)

 < 8 (reference)

 8–11

32.929

15.073

0.034

2.185

 > 11

46.007

15.670

0.046

2.936

Fertilization method

 IVF (reference)

 ICSI

− 17.118

10.853

− 0.016

− 1.577

 IVF + ICSI

0.574

13.917

< 0.001

0.041

Number of embryos transferred, ≥ 2 (versus 1)

14.579

11.651

0.012

1.251

Embryo developmental stage at transfer, day 5/6 (versus day 3)

70.051

12.674

0.053

5.527

Gestational age (weeks)

176.728

2.722

0.546

64.915

Newborn gender, female (versus male)

− 1.714

1.524

− 0.015

− 1.125