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Table 4 Risk ratios and 95% confidence intervals for the association between average monthly PCE exposure (g) during the LMP year and overall ischemic placental disease a among 2,110 index pregnancies

From: Prenatal drinking-water exposure to tetrachloroethylene and ischemic placental disease: a retrospective cohort study

     Model 1: Unadjusted GEE     Model 2: Multivariable GEEb  
  Events/N RR 95% CI RR 95% CI
Exposure categorized by any or the sample median      
  Any exposure 92/1,091 0.81 0.61, 1.07 0.86 0.65, 1.14
  ≥50th (5.7 × 10-1 g - 89.2 g) 55/635 0.82 0.59, 1.14 0.90 0.65, 1.24
  >0- < 50th (1.2 × 10-4 g – 5.7 × 10-1 g) 37/456 0.79 0.54, 1.15 0.82 0.55, 1.23
  0 104/1,019 1.00 Referent 1.00 Referent
Exposure categorized by 1980 action level (40 ppb)      
  ≥1.136 g (40 ppb) 39/480 0.77 0.54, 1.11 0.88 0.62, 1.26
  >0 - <1.136 g 53/611 0.83 0.60, 1.16 0.85 0.61, 1.20
  0 104/1,019 1.00 Referent 1.00 Referent
Exposure categorized in quartiles (percentiles)      
  ≥75th (2.3 g - 89.2 g) 26/331 0.77 0.50, 1.17 0.87 0.56, 1.35
  50th-75th (5.7 × 10-1 g - 2.3 g) 29/304 0.88 0.57, 1.35 0.91 0.60, 1.39
  25th-50th (1.3 × 10-1 g - 5.7 × 10-1 g) 20/261 0.72 0.44, 1.18 0.74 0.43, 1.26
  >0- < 25th (1.2 × 10-4 g – 1.3 × 10-1 g) 17/195 0.89 0.54, 1.46 0.95 0.58, 1.54
  0 104/1,019 1.00 Referent 1.00 Referent
  1. Abbreviations: CI confidence interval, GEE generalized estimating equation, LMP last menstrual period, PCE tetrachloroethylene, RR risk ratio.
  2. aIncluding placental abruption, preeclampsia, small for gestational age, and stillbirth at ≥27 weeks gestation.
  3. bAdjusted for maternal age during LMP year (<25 y, 25–29.9 y, 30–34.9 y, 35+ y), year pregnancy ended (<1974, 1975–1980, and >1980), prior ischemic placental disease (nulliparous, parous without history of ischemic placental disease, parous with history of ischemic placental disease), and first-trimester smoking (none, <11 cigarettes/day, ≥11 cigarettes/day).