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

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

		Model 1: Unadjusted GEE		Model 2: Multivariable GEE^b
	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

Abbreviations: CI confidence interval, GEE generalized estimating equation, LMP last menstrual period, PCE tetrachloroethylene, RR risk ratio.
^aIncluding placental abruption, preeclampsia, small for gestational age, and stillbirth at ≥27 weeks gestation.
^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).

ISSN: 1476-069X