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Table 1 Characteristics of the study subjects according to the method of pregnancy

From: The risk of secondary sex ratio imbalance and increased monozygotic twinning after blastocyst transfer: data from the Japan Environment and Children’s Study

Characteristics Spontaneous conception Non-ART treatment CT BT Spontaneous vs Non-ART treatment vs CT and BT
Mother (Pregnancies) (n) 92,022 3546 728 2020  
 Age (year) 30.4 ± 5.0 32.7 ± 4.2 35.6 ± 4.0 35.6 ± 3.9 <.0001
 BMI (kg/m2) 21.2 ± 3.3 21.4 ± 3.6 21.3 ± 3.0 21.3 ± 3.1 <.0001
 Metabolic equivalent/min 414.1 ± 732.9 334.8 ± 604.6 256.0 ± 488.1 258.6 ± 462.5 <.0001
 Calorie intake 385.4 ± 729.3 318.0 ± 597.4 235.0 ± 453.0 249.5 ± 551.8 <.0001
 Low education (%) 37.3 22.4 21.9 22.8 <.0001
 Smoking habit (%) 18.9 8.5 4.4 4.8 <.0001
 Alcohol consumption habit (%) 65.6 63.2 60.6 62.4 <.0001
 Physical component summary (SF-8 score) 45.3 ± 5.3 44.1 ± 7.6 43.7 ± 7.9 43.8 ± 8.2 <.0001
 Mental component summary (SF-8 score) 46.1 ± 7.3 46.9 ± 7.1 47.6 ± 7.2 47.0 ± 7.0 <.0001
 Assessing depression (K6 score) 3.7 ± 3.9 3.2 ± 3.4 2.8 ± 3.0 3.0 ± 3.4 <.0001
 Hyperlipidemia (%) 0.5 1.3 0.5 0.7 <.0001
 Diabetes (%) 0.2 0.4 0.5 0.5 <.0001
 Hyperthyroidism (%) 1.0 1.3 1.4 1.8 0.001
 Hypothyroidism (%) 0.9 2.1 3.4 3.9 <.0001
Family
 Low income (%) 41.5 26.8 16.7 20.2 <.0001
Father (n) 47,208 1929 410 1082  
 Age (year) 32.4 ± 5.8 34.4 ± 5.2 37.2 ± 5.4 37.6 ± 5.5 <.0001
 BMI (kg/m2) 23.4 ± 3.5 23.5 ± 3.4 23.9 ± 3.2 23.8 ± 3.3 <.0001
 Low education (%) 45.1 31.3 30.3 32.3 <.0001
 Smoking habit (%) 51.2 38.7 33.8 33.6 <.0001
 Alcohol consumption habit (%) 78.8 78.0 78.1 80.1 NS
 Physical component summary (SF-8 score) 51.0 ± 5.3 51.1 ± 5.3 51.2 ± 4.7 50.9 ± 5.3 NS
 Mental component summary (SF-8 score) 49.8 ± 6.1 49.9 ± 6.2 50.0 ± 6.2 50.1 ± 5.9 NS
 Assessing depression (K6 score) 2.6 ± 3.5 2.5 ± 3.4 2.3 ± 3.2 2.5 ± 3.5 NS
Infants (n) 92,545 3696 751 2102  
 Male (%) (95% CI) 51.3 (49.2–53.4) 50.7(48.6–52.8) 48.9 (45.3–52.5) 53.4 (51.3–55.5) NS
 Sex ratio 1.05 1.03 0.96 1.15  
Pregnancies (n) 92,022 3546 728 2020  
 Single (%) 99.4 95.8 96.8 95.9 <.0001
 Multiple (%) 0.6 4.2 3.2 4.1  
  [Monozygotic twinning (%)] (95% CI) 0.27 (0.23–0.30) 0.11 (0–0.22) 0.27 (0–0.65) 0.99 (0.56–1.42) <.0001
  1. Data are shown as mean ± SD (The percentages are drawn from available data and the total number varies for each category because of missing values and refer to the Additional file 2.). Smoking and alcohol consumption habits at pregnancy recognition, SF-8 score of 50 or less. Low education: defined by the highest academic background and categorized as graduation from high school or less, Low income: defined by the annual revenue of the household and categorized as an annual income of 4,000,000 Japanese yen or less. The P values are listed simply to give an indication of the magnitude of the inter-group differences. It is not intended that all those P values should have the customary probabilistic interpretation
  2. BMI (body mass index), CT (early cleavage-stage embryo transfer), BT (blastocyst transfer), NS (not statistically significant)