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Table 1 Maternal medical background and obstetric outcomes

From: Preconception vitamin D intake and obstetric outcomes in women using assisted reproductive technology: the Japan Environment and Children’s Study

Variable Quintile for VitD  
Q1 (low) Q2 Q3 Q4 Q5 (high)  
n = 18,592 n = 18,439 n = 18,368 n = 18,636 n = 18,536 P-value
Maternal medical background
 VitD intake before pregnancy, μg/day, median (IQR) 1.4 (0.8–1.8) 3.0 (2.6–3.3) 4.3 (4.0–4.7) 6.0 (5.5–6.7) 10.2 (8.6–12.8)  < 0.001a
 Maternal age, years, mean (SD) 30.0 (5.3) 31.0 (5.0) 31.4 (4.9) 31.8 (4.8) 31.8 (4.9)  < 0.001b
Advanced maternal age, %
  < 20 1.6 0.7 0.5 0.5 0.6  < 0.001c
 20–29 45.7 37.7 35.1 31.6 31.8
 30–39 49.1 57.4 59.6 62.8 62.3
  > 40 3.6 4.1 4.8 5.2 5.3
BMI before pregnancy (kg/m2), %
  < 18.5 17.2 16.6 15.8 15.7 15.1  < 0.001c
 18.5–25.0 71.7 73.1 74.0 73.9 73.1
  > 25.0 11.1 10.3 10.2 10.4 11.8
Smoking during pregnancy, % 6.6 4.7 4.3 3.9 4.6  < 0.001c
Primipara, % 51.3 42.5 39.2 35.8 32.7  < 0.001c
ART pregnancy, % 2.2 3.0 3.3 3.2 2.9  < 0.001c
Chronic Hypertension, % 1.3 1.1 1.1 1.2 1.3 0.240
Glucose intolerance, % 1.6 1.7 1.8 1.6 2.1 0.002
Endometriosis, % 3.0 3.6 3.8 3.8 3.9  < 0.001c
Maternal education, years, %
  < 10 7.1 4.6 4.1 3.8 4.5  < 0.001c
 10–12 38.6 32.9 29.6 27.5 29.1
 13–16 38.7 41.8 43.1 42.9 44.2
  > 17 15.7 20.8 23.2 25.8 22.2
Annual household income, %
  < 2,000,000 JPY 8.7 5.4 4.5 4.2 5.6  < 0.001c
 2,000,000–5,999,999 JPY 69.6 68.7 67.7 66.1 66.0
 6,000,000–9,999,999 JPY 18.5 21.9 23.4 24.7 23.7
  > 10,000,000 JPY 3.3 3.9 4.5 4.9 4.7
Daily calorie intake, kcal/day, median (IQR) 1307 (1049–1939) 1523 (1282–1813) 1657 (1416–1952) 1881 (1594–2637) 2254 (1850–3578)  < 0.001a
Obstetric outcomes
 PTB at < 37 weeks, % 4.5 4.8 4.5 4.4 4.8 0.768d
 PTB at < 34 weeks, % 0.9 1.0 0.9 0.8 1.0 0.676d
 LBW < 2500 g, % 8.2 8.3 7.8 7.5 8.2 0.175d
 LBW < 1500 g, % 0.6 0.6 0.5 0.5 0.6 0.443d
 SGA, % 5.1 5.0 4.6 5.0 5.6 0.031d
 HDP, % 3.3 3.1 2.9 3.1 3.1 0.360d
  1. VitD Vitamin D, n Number, IQR Interquartile range, SD Standard deviation, BMI Body mass index, ART Assisted reproductive technology, JPY Japanese Yen, PTB Preterm birth, LBW Low-birth weight infant, SGA Small for gestational age, HDP Hypertensive disorder of pregnancy
  2. a Kruskal–Wallis analysis
  3. b One-way analysis of variance
  4. c Chi-square test
  5. d Mantel–Haenszel’s chi-square test for linear trends