Table 2 Univariate liner analysis of impact factors on birthweight (n = 1846)

Maternal age (y)

30.92 ± 3.95

−1.20 (−6.12, 3.73)

0.6338

Paternal age (y)

32.46 ± 4.77

−0.37 (−4.44, 3.70)

0.8571

Maternal BMI (kg/m²)

22.25 ± 3.12

15.97 (9.79, 22.15)

< 0.0001

Basal FSH

7.66 ± 2.46

−1.05 (− 8.95, 6.85)

0.7948

AMH

2.87 ± 2.24

5.09 (−3.57, 13.75)

0.2495

Type of infertility

  Primary

934 (50.60%)

Ref

  Secondary

912 (49.40%)

30.32 (−8.50, 69.14)

0.1260

Infertility duration (y)

3.65 ± 2.69

−6.65 (−13.85, 0.56)

0.0708

Infertility cause

  Female

1196 (64.79%)

Ref

  Male

362 (19.61%)

−27.00 (−77.04, 23.05)

0.2906

  Mixed

175 (9.48%)

25.37 (−42.16, 92.89)

0.4616

  Unexplained

113 (6.12%)

−34.34 (− 116.45, 47.77)

0.4125

Prior gonadotropin cycle

1.22 ± 0.54

−9.29 (−44.99, 26.41)

0.6101

COS protocols

  GnRH-a long protocol

1211 (65.60%)

Ref

  Antagnist protocol

635 (34.40%)

−52.70 (−94.43, −10.96)

0.0134

Dosage of gonadotropins (IU)

2277.14 ± 1114.47

0.02 (−0.00, 0.03)

0.0764

Stimulation duration (days)

11.57 ± 2.20

9.36 (0.55, 18.18)

0.0375

E2 level on HCG day (100 pg/ml)

29.96 ± 12.67

−5.49 (−8.83, −1.23)

0.023

Number of oocytes retrieved

9.68 ± 3.81

2.63 (− 2.47, 7.72)

0.3120

Fertilization method

  IVF

1218 (65.98%)

Ref

  ICSI

535 (28.98%)

−29.85 (−73.09, 13.39)

0.1762

  IVF + ICSI

93 (5.04%)

−92.14 (−182.74, − 1.54)

0.0464

Stage embryo transferred

  D3

1542 (83.53%)

Ref

  D5

304 (16.47%)

13.04 (−39.32, 65.40)

0.6255

Number of embryos transferred

  1

498 (26.98%)

Ref

  2

1344 (72.81%)

22.23 (−21.54, 66.00)

0.3197

  3

4 (0.22%)

141.86 (− 276.99, 560.71)

0.5069

Endometrial thickness (mm)

9.97 ± 1.53

8.59 (−4.09, 21.27)

0.1844

Endometrial type

  A

28 (1.52%)

Ref

  A-B

104 (5.63%)

54.59 (− 122.82, 232.01)

0.5465

  B

564 (30.55%)

91.85 (−69.49, 253.20)

0.2646

  B-C

1023 (55.42%)

106.98 (−52.65, 266.60)

0.1892

  C

127 (6.88%)

183.22 (9.24, 357.19)

0.0391

Gender of newborn

  Male

927 (50.22%)

Ref

  Female

919 (49.78%)

−109.08 (− 147.60, − 70.56)

< 0.0001