Table 2 Independent dataset characteristics. Double stratification of data by age (< 35; 35–37, 38–40, 41–43, > 43 years), and by different subgroups of maternal (uterus) age, oocyte age, and oocyte source (autologous and donor oocyte recipient). Odds ratio (OR) and P-values for the associations between each subgroup and fetal heartbeat (FH) rate is shown. Mean AI score per age category is also shown. All transferred embryos in this analysis had known FH clinical outcomes

Maternal (Uterus) Age

Transferred embryos (n)

408

287

235

140

98

known transfer outcomes (n)

337

238

195

119

73

FH + embryos (n)

175

123

84

54

43

FH rate (%)

[95% CI]

51.92 [46.60–57.30]

51.68 [45.30–58.10]

43.07 [36.10–50.10]

45.37 [36.30–54.50]

58.90 [47.30–70.50]

Age

(mean ± SD, years)

31.8 ± 2.26

36.0 ± 0.80

39.0 ± 0.86

41.8 ± 0.77

45.8 ± 1.83

OR

[95% CI]

1.09

[0.88–1.30]

0.98 [0.70–1.36]

0.70 [0.49–0.99]

0.76 [0.50–1.16]

1.32 [0.79–2.20]

P-value

0.443

0.884

0.045

0.208

0.291

AI score (mean ± SD)

6.06 ± 2.67

5.98 ± 2.57

5.60 ± 2.73

5.74 ± 2.73

6.86 ± 1.98

Oocyte Age

Transferred embryos (n)

598

258

200

74

10

Known transfer outcomes (n)

486

214

172

66

10

FH + embryos (n)

273

111

68

20

1

FH rate (%)

[95% CI]

56.17 [51.70–60.60]

51.86 [45.10–58.60]

39.53 [32.20–46.90]

30.30 [18.90–41.70]

10.0

[0.0-32.60]

Age

(mean ± SD, years)

29.6 ± 4.41

36.0 ± 0.811

38.9 ± 0.877

41.7 ± 0.766

44.1 ± 0.316

OR [95% CI]

1.29

[1.08–1.53]

0.83 [0.60–1.15]

0.507 [0.36–0.72]

0.34

[0.19–0.59]

0.09

[0.01–0.69]

P-value

0.006

0.254

< 0.01

< 0.01

0.021

AI score (mean ± SD)

6.43 ± 2.43

5.90 ± 2.64

5.39 ± 2.81

4.67 ± 2.92

5.43 ± 1.79

Autologous IVF Cycles

Transferred embryos (n)

394

258

200

74

10

Known transfer outcomes (n)

329

214

172

66

10

FH + embryos (n)

168

111

68

20

1

FH rate (%)

[95% CI]

51.06 [45.60–56.50]

51.86 [45.10–58.60]

39.53 [32.20–46.90]

30.30 [18.90–41.70]

10.0 [0.0-32.60]

Age (mean ± SD)

31.8 ± 2.26

36.0 ± 0.811

38.9 ± 0.877

41.7 ± 0.766

44.1 ± 0.316

OR [95% CI]

1.05 [0.85–1.31]

1.017 [0.72–1.44]

0.62 [0.43–0.91]

0.41 [0.24–0.73]

0.11 [0.01–0.84]

P-value

0.657

0.924

0.013

0.002

0.034

AI Score (mean ± SD)

6.04 ± 2.68

5.90 ± 2.64

5.39 ± 2.81

4.67 ± 2.92

5.43 ± 1.79

Donor Oocyte Recipient IVF Cycles

Transferred embryos (n)

14

29

35

66

88

Known transfer outcomes (n)

8

24

23

53

63

FH + embryos (n)

7

12

16

34

42

FH rate (%)

[95% CI]

87.5 [57.90–100.00]

50.0 [28.40–71.60]

69.56 [49.20–89.90]

64.15 [50.80–77.50]

66.67 [54.70–78.60]

Oocyte age (mean ± SD, years)

27.6 ± 4.25

24.3 ± 4.43

25.5 ± 4.56

25.7 ± 4.74

25.0 ± 4.20

Maternal age

(mean ± SD)

31.9 ± 2.16

36.2 ± 0.689

39.3 ± 0.701

42.0 ± 0.754

46.0 ± 1.83

OR [95% CI]

7.00 [0.86–56.90]

0.14 [0.02–1.35]

0.33 [0.03–3.18]

0.26 [0.03–2.24]

0.29 [0.03–2.48]

P-value

0.068

0.089

0.335

0.217

0.255

AI score (mean ± SD)

6.62 ± 2.38

6.73 ± 1.68

6.80 ± 1.85

6.93 ± 1.89

7.02 ± 1.95