Journal of Environmental Protection, 2011, 2, 683-691
doi:10.4236/jep.2011.26079 Published Online August 2011 (http://www.SciRP.org/journal/jep)
683
Persistent Organochlorine Exposure and
Pregnancy Loss: A Prospective Cohort Study
Anna Z. Pollack1, Germaine M. Buck Louis1, Courtney D. Lynch2, Paul J. Kostyniak3
1Epidemiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, USA;
2Division of Epidemiology & Department of Obstetrics and Gynecology, Ohio State University, Columbus, USA; 3Department of
Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University of New York, Buffalo, USA.
Received March 23rd, 2011; revised May 6th, 2011; accepted June 21st, 2011.
ABSTRACT
Polychlorinated biphenyls (PCBs) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) are suspected reproductive
toxicants. We assessed serum concentration of 76 PCB congeners, DDE, and risk of human chorionic gonadotropin
confirmed pregnancy loss among 79 women followed for up to 12 menstrual cycles or until pregnancy. 55 women had
live births, 14 experienced pregnancy losses, and 10 did not achieve pregnancy. PCBs and DDE were quantified using
gas chromatography with electron capture. PCBs were grouped a priori by biologic activity. Cox proportional hazard
regression adjusting for age (categorized 24 - 29, 30 - 34) and average stand ardized alcoho l and cigarette in take (con-
tinuous) was used to estimate hazard ratios (HR) of pregnancy loss. Estrogenic PCBs (HR = 1.66, 95% CI: 0.68, 4.02),
anti-estrogenic PCBs (HR = 0.10, 95% CI: <0.01, 67.07) and DDE (HR = 1.43, 95% CI: 0.45, 4.52) were not statisti-
cally significantly associated with pregnancy loss. Our results provide some signal that estrogenic and antiestrogenic
PCBs may be differentially associated with pregnancy loss. Further research is needed to elucidate these associations.
Keywords: 1,Dichloro-2,2-Bis(P-Chlorophenyl)Ethylene, Fecundity, Organochlorine, Polychlorinated Biphenyl,
Pregnancy Loss
1. Introduction
Fecundity is defined as the biologic capacity for repro-
duction [1] and can be conceptualized to include im-
pairments such as conception delay, infertility, or preg-
nancy loss. Fecundity is an essential aspect when assess-
ing potential reproductive or developmental toxicity of
environmental agents. Exposures adversely impacting
fecundity can be identified by estimating differences in
the time-to-pregnancy among exposed women relative to
unexposed women [2] or in estimating the risk of preg-
nancy loss [3]. There has been speculation that a global
reduction in human fecundity is underway [4]. Available
evidence suggests that environmental agents, particularly
the endocrine disrupting class of chemicals, may contrib-
ute to this decline [5].
Recent reviews have summarized the available evi-
dence regarding the reproductive and/or developmental
toxicity (RADT) of persistent organochlorines such as
polychlorinated biphenyls (PCBs) and 1,1-dichloro-2,2-
bis(p-chlorophenyl)ethylene (DDE) [6-8]. Past research
has attempted to assess the potential RADT of polyhalo-
genated aromatic hydrocarbons in relation to human fe-
cundity, but often has relied upon proxy exposure meas-
urements such as PCB contaminated fish consumption
[9,10], occupation [11], residence [12], or quantified se-
rum or plasma concentrations often collected years fol-
lowing reproductive outcomes [13,14]. Estimating the
effect of environmental chemical exposure and preg-
nancy loss is challenging for many reasons, including the
high proportion of losses occurring prior to (woman/
clinical) recognition and the competing risk of infertility,
in that women who do not conceive are not at risk of
pregnancy loss. Prospective cohort designs with precon-
ception recruitment of women or couples and with bio-
monitoring of human chorionic gonadaotropin (hCG)
pregnancy remains the gold standard for assessing envi-
ronmental RADT, particularly those occurring in the
sensitive periconceptional window [15,16]. While chal-
lenging, the utility and feasibility of such approaches
have been established [17].
Spontaneous pregnancy loss is a sensitive endpoint in-
dicative of impaired fecundity. In relation to DDT expo-
sure, pregnancy loss has been assessed by questionnaire

Persistent Organochlorine Exposure and Pregnancy Loss: A Prospective Cohort Study 684
with no effect [14] while a positive association was
found with an hCG biomarker of pregnancy loss [18].
Repeated miscarriage was not related to organochlorine
exposure when pregnancy loss was assessed by maternal
recall [19,20]. Prospectively observed pregnancy loss
and organochlorine exposure have yet to be assessed
using biomarkers of PCB, DDE, and pregnancy. The
paucity of literature on the potential influence of envi-
ronmental factors on fecundity impairments, coupled with
the growing consensus that such an effect is present mo-
tivated the current study. We assessed the relation be-
tween PCB and DDE concentrations and risk of hCG
pregnancy loss in a cohort of women recruited prior to
conception and followed until pregnant or through 12
menstrual cycles at risk for pregnancy.
2. Methods
The study cohort was recruited from a referent cohort
comprising 2,637 women aged 18 - 44 years who par-
ticipated in a population-based angler cohort study whose
aim was to assess species specific fish consumption and
knowledge of consumption advisories. Specifically, women
who stated in 1991 that they were either considering or
undecided about future pregnancies were re-contacted in
1996 - 1997 and asked to participate in a prospective
pregnancy study, providing they were 40 years of age,
had no physician-diagnosed infertility and were planning
to begin trying to become pregnant in the next six
months. Among the 244 eligible women, 113 (46%) were
recruited, of which 14 were found to be pregnant at or
immediately following enrollment, leaving 99 women in
the study cohort. An additional 20 women withdrew from
the study without an observed pregnancy. Of the 79
women completing follow-up, 69 (87%) became preg-
nant, of which 55 (80%) had live births and 14 (20%)
experienced pregnancy losses. Ten (13%) women did not
achieve pregnancy (i.e., infertile). The study was ap-
proved by the Institutional Review Board for the School
of Medicine and Biomedical Sciences at the University at
Buffalo, State of New York; all women provided in-
formed consent prior to their participation.
Women participated in a baseline interview adminis-
tered by a research registered nurse and were instructed
in the accurate use of the Clearblue EasyTM home preg-
nancy test, capable of detecting 50 mIU/ml of hCG (per
manufacturer) in urine on the date of expected menses.
Clearblue Easy is a digital pregnancy test kit that dis-
plays “pregnant”, “not pregnant”, or “error” for simple
interpretation. This pregnancy test is one of the most
sensitive and accurate presently available [21]. Partici-
pants were instructed to use pregnancy tests on the first
day menses was expected and one week later, regardless
of the first result, and to complete daily diaries while
trying to become pregnant to obtain information on men-
struation, sexual intercourse and lifestyle exposures that
may adversely affect fecundity, including pregnancy loss
(i.e., cigarette smoking and consumption of caffeine and
alcohol). Reminder telephone calls were placed by the
research nurse when diary cards were a week late. A
non-fasting blood sample (10 ml) was collected at the
baseline interview by the research nurse utilizing
venipuncture collection equipment determined to be free
of the chemical exposures of interest in the study.
Serum samples were analyzed by the Toxicology Re-
search Center at the University at Buffalo (Buffalo, NY,
USA), for 76 congeners (64 single and 12 di-eluting
congeners) using gas chromatography with electron cap-
ture detection as previously described [22,23]. Briefly,
ten samples were run in each batch, including four con-
trols consisting of one reagent blank, one matrix blank,
one quality control sample and one duplicate sample [22].
PCB congeners were categorized a priori by purported
biologic activity and summed () into four groupings: 1)
total PCBs or the  of all measured congeners; 2)  es-
trogenic congeners (# 4_10, 5_8, 15_17, 18, 31, 44, 47,
48, 52, 70, 99, 101, 136, 153, 188); 3)  anti-estrogenic
congeners (# 77_110, 105, 114, 126, 156_171, 169); and
4)  other PCB congeners (#6, 7_9, 16_32, 19, 22,
24_27, 25, 28, 33, 40, 42, 45, 50, 55, 59, 60, 64, 66_95,
74, 81_87, 82, 94, 97, 118, 128, 129, 132, 134, 135, 138,
141, 147, 149, 151, 157_200, 163, 167, 170, 172, 174,
176, 177, 179, 180, 181, 183, 185, 187, 189, 190, 194,
195, 196_203, 205, 206) [24,25]. PCB and DDE values
were corrected only for recovery; no substitution of val-
ues below the laboratory limits of detection were made to
avoid introducing potential bias [26,27]. We did not ad-
just PCBs or DDE for serum lipids, given the absence of
evidence supporting a causal relation between serum
lipids and pregnancy loss [28]. Serum PCB and DDE
concentrations are expressed as nanogram/gram (ng/g)
serum, which is equivalent to parts per billion. Total lip-
ids (TL) were quantified using enzymatic methods as a
function of total cholesterol (TC), free cholesterol (FC),
triglycerides (TG) and phospholipids (PL) as:
TL = 1.677 (TC − FC) + FC + TG + PL, and were ex-
pressed in mg/dl [29].
The primary outcome of interest was pregnancy loss.
Early pregnancy loss was defined as a positive pregnancy
test followed by a negative test or by clinical confirma-
tion of pregnancy followed by clinical pregnancy loss,
which was defined as loss following clinical confirma-
tion of pregnancy. Clinical pregnancy losses were self-
reported, though all women who had hCG confirmed
pregnancies were followed for approximately eight weeks’
gestation. All clinical losses occurred prior to 20 weeks’
gestation as reported by women. In our analyses, total

Persistent Organochlorine Exposure and Pregnancy Loss: A Prospective Cohort Study 685
pregnancy loss included early and clinical loss.
Lifestyle covariates (caffeine, alcohol, and cigarettes
smoked) were reported daily using the diary and were,
subsequently, standardized to a 28-day cycle to account
for the intra- and inter-woman variability in menses.
Number of caffeinated (coffee, tea, or soda) and alco-
holic drinks and number cigarettes smoked per day were
recorded on the daily diary. Specifically, we summed the
woman’s reported consumption over her menstrual cycle
(which may be longer or shorter than 28 days), multi-
plied it by 28 and then divided by the number of days in
her cycle. Failing to standardize lifestyle exposures could
make it seem that women with shorter menstrual cycles
consumed less, because they had less opportunity for
consumption at each cycle; conversely, that women with
longer cycles consumed more given their longer length
of follow-up. Caffeine and alcohol consumption and
cigarette smoking were selected because of their possible
shared detoxification pathway with PCBs and DDE via
cytochrome P450 (CYP450) [30]. High levels of lifestyle
covariates could lead to overloading this pathway; alter-
natively, individuals with high lifestyle covariate levels
could have CYP450 pathways that are better suited to
detoxification. Confounders were selected based on a
priori knowledge.
Descriptive population statistics were tabulated by
study outcome variable, and by completion of the study
protocol. Pearson’s Chi Square and ANOVA p-values
were calculated to detect statistically significant differ-
ences (p < 0.05) between study outcome and completion
of the study protocol.
Although all participants provided blood samples,
some women did not have sufficient sample to quantify
all congeners (10%) or individual lipid (30%) compo-
nents necessitating the use of multiple imputation. Ciga-
rette and alcohol consumption were imputed for two in-
dividuals with insufficient daily diary data, but who
completed follow-up. Multiple imputation was used to
estimate the missing values to avoid potential biases as-
sociated with mean or median imputation, or complete
case analysis [31-33] using Imputation by Chained Equa-
tions (ICE) in STATA version 9 (StataCorp, College
Station, TX).
Cox proportional hazard regression was used to esti-
mate hazard ratios (HRs) of pregnancy loss (early and
clinical losses combined) when restricting to women
achieving pregnancy while under observation. Censoring
occurred after 20 weeks of pregnancy. We estimated the
hazard of pregnancy loss for PCB and DDE concentra-
tions when left as continuous or categorical exposures.
Models for pregnancy loss were run separately for total
PCBs, estrogenic PCBs, anti-estrogenic PCBs, other
PCBs, and DDE. Additionally, estrogenic PCBs, anti-
estrogenic PCBs, other PCBs, and DDE were run to-
gether as continuous variables in one model, to determine
if the results from the individual models were altered,
perhaps due to a competing mechanism of action. We
presented all models with and without adjustment for age
(categorized as 24 - 29 and 30 - 34) and average stan-
dardized alcohol and cigarette intake over a 28-day men-
strual cycle (continuous). We did not include parity as a
covariate because it may be on the causal pathway to
pregnancy loss, and may induce over adjustment bias
[34,35]. Additionally, we emphasize that given our small
sample size, our statistical models are not robust to
stratifying by parity to further assess this issue. STATA
version 9 was used for all analyses.
3. Results
All women completed baseline interviews and returned
95% of expected daily diary cards. Women who with-
drew from the study either before achieving pregnancy or
completing 12 menstrual cycles with intercourse during
the fertile window were not systematically different from
women completing the study with regard to age, gravid-
ity, parity, BMI, or smoking, alcohol and cigarette con-
sumption (data not shown). Gravidity was associated
with pregnancy loss (Table 1). However, age, body mass
index (kg/m2), smoking, alcohol, and cigarette consump-
tion were not statistically associated with pregnancy loss,
infertility, or live birth.
Women with a live birth had a broader range of total
PCB levels, 2.58 to 14.51 ng/g serum, compared to
women with a pregnancy loss, 3.89 to 9.09 ng/g serum
(Table 2). Estrogenic PCBs were similarly distributed,
and women with a live birth ranged from a minimum of
0.07 to a maximum of 9.19 ng/g serum, whereas women
with a pregnancy loss ranged between 1.63 to 4.52 ng/g
serum. Women with a live birth had a greater range of
DDE levels, from <0.01 to 3.37 ng/g serum, compared to
those with a pregnancy loss, from 0.41 to 1.63 ng/g se-
rum. Anti-estrogenic PCBs and other PCBs similarly had
a slightly wider range among women with a live birth
than women with a pregnancy loss (Table 2).
No statistically significant differences in PCB or DDE
concentrations were observed by outcome (Table 2).
Total PCBs were lowest among women who did not
achieve pregnancy over 12 prospectively observed men-
strual cycles (4.62 ng/g serum), and highest among
women with a live birth (5.26 ng/g serum), although this
difference was not statistically significant. Median es-
trogenic PCB levels were similar among women who had
a live birth (2.20 ng/g serum) and those who had a preg-
nancy loss (2.16 ng/g serum). DDE was marginally
higher among women with apregnancy loss (1.06 ng/g

Persistent Organochlorine Exposure and Pregnancy Loss: A Prospective Cohort Study 686
Table 1. Sociodemographic characteristics of cohort by study outcome (n = 79).
Characteristic Live Birth n (%) Pregnancy Loss n (%) Infertile n (%) P value
55 (70) 14 (17) 10 (13)
Age (in years) 0.25
<30 19 (34) 8 (57) 5 (50)
30 36 (65) 6 (43) 5 (50)
Gravidity (# live births) 0.01
0 10 (18) 6 (43) 6 (75)
1 36 (65) 5 (36) 1 (12)
2+ 9 (16) 3 (21) 1 (12)
Parity (# pregnancies) 0.10
0 8 (14) 5 (36) 5 (50)
1 24 (44) 4 (28) 3 (30)
2+ 23 (42) 5 (36) 2 (20)
Body mass index (kg/m2) 0.88
<25 34 (62) 9 (64) 7 (70)
25 21 (38) 5 (36) 3 (30)
Mean (SDb)
Daily # cigarettes smoked 1.9 (4.5) 0.4 (1.4) 0.4 (1.3) 0.28
Daily # alcoholic beverages 0.3 (0.3) 0.2 (0.5) 0.5 (0.4) 0.33
Daily # caffeinated beverages 1.8 (1.5) 0.9 (0.9) 1.4 (1.2) 0.10
NOTE: Cigarette usage was imputed for 9 women, 9 for alcohol and 9 for caffeine consumption. Gravidity is missing for 2 women. Excludes 20 women who
withdrew from study before an outcome. aTTP, denotes number of menstrual cycles at risk for pregnancy. bSD, denotes standard deviation.
Table 2. Median serum concentration of polychlorinated biphenyl (PCBs) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene
(DDE) concentrations by study outcome (n = 79).
Serum Concentration
(ng/g serum)
Live Birth (n = 55)
Median (min, max)
Pregnancy Loss (n = 14)
Median (min, max)
Infertile (n = 10)
Median (min, max)
Total PCBs 5.26 (2.58, 14.51) 5.14 (3.89, 9.09) 4.62 (4.09, 11.08)
Estrogenic PCBs 2.20 (0.07, 9.19) 2.16 (1.63, 4.52) 1.99 (0.63, 5.99)
Anti-estrogenic PCBs 0.20 (<0.02, 0.68) 0.18 (0.03, 0.32) 0.22 (0.06, 0.35)
Other PCBs 2.88 (1.58, 9.07) 2.83 (2.04, 4.68) 2.47 (2.23, 4.99)
DDE 0.93 (<0.01, 3.37) 1.06 (0.41, 1.63) 0.80 (0.47, 3.59)
Serum lipids (mg/dL) 558.35 (369.67, 881.49) 555.95 (324.20, 967.13) 537.74 (402.55, 713.80)
Note: Cigarette usage was imputed for 9 women, 9 for alcohol and 9 for caffeine consumption. Gravidity is missing for 2 women. Excludes 20 women who
withdrew from study before an outcome.
serum) compared to those with a live birth (0.93 ng/g
serum).
Total PCBs, estrogenic PCBs, anti-estrogenic PCBs
and DDE were not statistically significantly associated
with the adjusted hazard of pregnancy loss (Table 3).
However, the point estimates were greater than one for
total and estrogenic PCBs and DDE and less than one for
anti-estrogenic PCBs. Relative to the lowest tertile, the
aHR for pregnancy loss among those in the highest DDE
tertile was 1.45 (95% CI: 0.3, 5.70). The highest estro- 7

Persistent Organochlorine Exposure and Pregnancy Loss: A Prospective Cohort Study687
Table 3. Serum concentration of polychlorinated biphenyl (PCBs) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE)
concentrations and hazard of pregnanc y loss (n = 69).
Serum Concentration (ng/g serum) Unadjusted HR (95% CI) Adjusted HR (95% CI)a
Total PCBs
Low (1.62 - 5.02) 1.00 (referent) 1.00 (referent)
Medium (5.03 - 5.71) 1.06 (0.28, 4.00) 0.98 (0.25, 3.82)
High (5.72 - 12.68) 0.98 (0.26, 3.66) 1.20 (0.31, 4.67)
Total PCBs (continuous) 1.04 (0.77, 1.50) 1.15 (0.84, 1.58)
Estrogenic PCBs:
Low (1.49 - 2.06) 1.00 (referent) 1.00 (referent)
Med (2.07 - 2.28) 0.59 (0.16, 2.23) 0.60 (0.16, 2.31)
High (2.29 - 4.53) 0.75 (0.21, 2.66) 0.86 (0.23, 3.11)
Estrogenic PCBs (continuous) 1.61 (0.64, 4.02) 1.66 (0.68, 4.02)
Anti-estrogenic PCBs:
Low (0.02 - 0.16) 1.00 (referent) 1.00 (referent)
Med (0.17 - 0.22) 0.70 (0.21, 2.35) 0.83 (0.24, 2.85)
High (0.23 - 0.65) 0.48 (0.12, 1.97) 0.71 (0.16, 3.10)
Anti-estrogenic PCBs (continuous) 0.03 (<0.01, 18.79) 0.10 (<0.01, 67.07)
Other PCBs:
Low (1.97 - 2.70) 1.00 (referent) 1.00 (referent)
Med (2.71 - 3.11) 1.43 (0.35, 5.80) 1.61 (0.39, 6.72)
High (3.12 - 9.07) 1.25 (0.30, 5.32) 1.70 (0.38, 7.49)
Other PCBs (continuous) 0.99 (0.58, 1.70) 1.09 (0.66, 1.81)
DDE
Low (0.39 - 0.82) 1.00 (referent) 1.00 (referent)
Med (0.83 - 1.14) 1.07 (0.28, 4.06) 1.08 (0.28, 4.21)
High (1.15 - 3.60) 1.21 (0.32, 4.59) 1.45 (0.37, 5.70)
DDE (continuous) 1.09 (0.38, 3.15) 1.43 (0.45, 4.52)
NOTE: Estrogenic PCBs includes  congeners 4_10, 5_8, 15_17, 18, 31, 44, 47, 48, 52, 70, 99, 101, 136, 153, 188; anti-estrogenic PCBs includes  congeners
77_110, 105, 114, 126, 156_171, 169; and other includes  PCB congeners 6, 7_9, 16_32, 19, 22, 24_27, 25, 28, 33, 40, 42, 45, 50, 55, 59, 60, 64, 66_95, 74,
81_87, 82, 94, 97, 118, 128, 129, 132, 134, 135, 138, 141, 147, 149, 151, 157_200, 163, 167, 170, 172, 174, 176, 177, 179, 180, 181, 183, 185, 187, 189, 190, 194,
195, 196_203, 205, 206. Analysis restricted to women becoming pregnant while under observation in the prospective cohort. Cox proportional hazards regression.
aAdjusted for: age (24 - 30 versus 30 - 34) and mean alcohol consumption and cigarette smoking standardized to a 28-day menstrual cycle.
genic PCB tertile was not positively associated with
pregnancy loss when compared with the lowest estro-
genic PCB tertile (aHR = 0.86, 95% CI: 0.23, 3.11).
When continuous estrogenic, anti-estrogenic, and other
PCBs and DDE were jointly included in the model, es-
trogenic PCBs (aHR = 1.77, 95% CI: 0.34, 9.25) and
DDE (aHR = 1.68, 95% CI: 0.50, 5.61) yielded positive
point estimates and wide confidence intervals that in-
cluded the null (Table 4). We conducted sensitivity
analyses first restricting the models to women with com-
plete exposure data (no imputations) and then substitut-
ng log transformed PCB and DDE values for the raw i

Persistent Organochlorine Exposure and Pregnancy Loss: A Prospective Cohort Study 688
Table 4. Hazard of pregnancy loss and serum concentration of polychlorinated biphenyl (PCBs) and 1,1-dichloro-2,2-bis
(p-chlorophenyl)ethylene (DDE) analyzed jointly (n = 69).
Serum Concentration (ng/g serum) Unadjusted HR (95% CI) Adjusted HR (95% CI)a
Estrogenic PCBs 1.64 (0.29, 9.36) 1.77 (0.34, 9.25)
Anti-estrogenic PCBs 0.02 (<0.01, 196.01) 0.09 (<0.01, 632.71)
Other PCBs 0.96 (0.18, 5.09) 0.91 (0.19, 4.41)
DDE 1.38 (0.44, 4.39) 1.68 (0.50, 5.61)
NOTE: Estrogenic PCBs includes  congeners 4_10, 5_8, 15_17, 18, 31, 44, 47, 48, 52, 70, 99, 101, 136, 153, 188; anti-estrogenic PCBs includes  congeners
77_110, 105, 114, 126, 156_171, 169; and other includes  PCB congeners 6, 7_9, 16_32, 19, 22, 24_27, 25, 28, 33, 40, 42, 45, 50, 55, 59, 60, 64, 66_95, 74,
81_87, 82, 94, 97, 118, 128, 129, 132, 134, 135, 138, 141, 147, 149, 151, 157_200, 163, 167, 170, 172, 174, 176, 177, 179, 180, 181, 183, 185, 187, 189, 190, 194,
195, 196_203, 205, 206. Analysis restricted to women becoming pregnant while under observation in the prospective cohort. Cox proportional hazards regression.
aAdjusted for: age (24 - 30 versus 30 - 34) and mean alcohol consumption and cigarette smoking standardized to a 28-day menstrual cycle.
measurements and observed similar results (data not
shown).
4. Discussion
Our prospective pregnancy study with preconception
enrollment of women and a sensitive hCG biomarker of
pregnancy did not find statistically significant associa-
tions between DDE, total, estrogenic, and anti-estrogenic
PCBs, and pregnancy loss. The point estimates for an-
ti-estrogenic PCBs were less than one, possibly suggest-
ing a different direction of effect, but the estimate was
imprecise. One possible explanation for the suggestion of
a protective effect on the hazard of pregnancy loss for
anti-estrogenic PCBs may be attributed to the concept of
competing risk. If an exposure reduces pregnancy likeli-
hood, fewer losses would be expected, given that preg-
-nancy is a necessary criterion for a loss. Anti-estrogenic
PCB concentrations were associated with a reduction in
fecundability or a longer time to pregnancy for this co-
hort [25]. In this cohort, 6- and 12-month cumulative
pregnancies were 76% and 94%, which are similar to the
two other prospective pregnancy studies conducting 12
month follow-up of couples. Cumulative 6-and 12-cycle
pregnancy rates for other prospective cohort studies fol-
lowing women through 12 cycles ranged from 81% -
90% [36] and 92% - 95% [37].
Another explanation may be attributed to the labora-
tory precision in measuring the anti-estrogenic PCB
congeners or the absence of uniform criteria for grouping
congeners with regard to biologic activity. The sugges-
tion of opposing directions for our point estimates by
congener grouping supports the need to more fully assess
the mixture of compounds in relation to sensitive repro-
ductive and developmental outcomes, particularly in pre-
conception cohort studies with ample power for the de-
tection of pregnancy losses.
The only other prospective cohort study that utilized
preconception enrollment of women, enabling the au-
thors to identify incident pregnancy losses found a posi-
tive association between pregnancy loss and DDT [18].
Specifically, 388 nulliparous Chinese women provided a
blood specimen for the quantification of serum DDE and
daily urine samples for up to one year for the detection of
hCG pregnancy. An increased odds ratio (OR) for early
pregnancy loss of 1.17 (95% CI: 1.05, 1.29) was associ-
ated with a 10-ng/g increase in serum total DDT, and in a
categorical analysis comparing the third tertile of expo-
sure to the first, found an adjusted OR 2.12 (95% CI:
1.26, 3.57) [18]. Concentrations were notably higher
among the Chinese women (median p,p’-DDE and total
DDT of 26.24 ng/g and 27.9, respectively) than in our
study (median DDE 0.97 ng/g), possibly reflecting the
more recent use of DDT in China compared to the United
States [38]. Increased odds of spontaneous abortion have
been associated for DDE in a subset of the US Collabo-
rative Pregnancy Cohort, which recruited already preg-
nant women at median gestational age 21 weeks [14,39].
A small case control study of 30 Chinese factory workers
also reported that p,p’-DDE was associated with a 1.13
(CI: 1.02, 1.26) increased odds of spontaneous pregnancy
loss [13]. Lastly, support for an association between PCB
and/or DDE exposure and pregnancy loss comes from
several studies that relied upon retrospectively reported
exposures or outcomes and often without added attention
to the role of lactation history in mediating effects
[40-42]. Women with pregnancy losses have less oppor-
tunity to decrease their body burden of PCBs and DDE
than women giving birth, especially if they opt to breast-
fed. Retrospective exposures that rely on complex decay
models for estimating exposures at some time in the past
such as during pregnancy may be a source of potential
exposure misclassification [43]. Our results are not in-
consistent with the existing literature on DDE and are
subject to limited power, though the direction of effect,
particularly for DDE, signals a similar direction of effect
as prior work.

Persistent Organochlorine Exposure and Pregnancy Loss: A Prospective Cohort Study689
The mechanism of action by which DDE interferes
with pregnancy maintenance is not known, but DDE
isomers are believed to act similarly to estradiol [44,45]
and, thereby, may interfere with endocrine function. Al-
ternatively, DDE and PCBs have been demonstrated to
induce cytochrome P450 hepatic enzymes, which could
interfere with normal hormonal production necessary for
pregnancy maintenance [46,47] or the metabolism of
other xenobiotics, which may enhance or diminish hor-
monal or biochemical processes [48,49]. Further, persis-
tent organochlorine compounds may disrupt the placental
cell sodium channel barrier and, thereby, affect proges-
terone receptor binding [14].
5. Conclusions
We sought to assess a mixture of persistent organochlo-
rine compounds in relation to impaired fecundity, par-
ticularly the risk of pregnancy loss, to better model hu-
man exposures by addressing biological mechanism of
action. The use of daily diaries for ascertaining lifestyle
exposures believed relevant for human fecundity is ad-
vantageous, since women reported lifestyle exposures
prior to knowledge of pregnancy outcome. We system-
atically ascertained pregnancy via sensitive home preg-
nancy test kits, and we know no a priori reason why test
results would vary by exposure status. Our findings await
replication from larger cohort studies with preconception
enrollment and longitudinal data collection with the
eventual expectation of filling critical data gaps regard-
ing the impact of persistent compounds on sensitive
markers of human reproduction and development.
Our findings are not inconsistent with prior findings of
an association between DDE and estrogenic PCBs and
pregnancy loss. Though limited by a lack of power, our
results underscore the value of efforts to measure chemi-
cal mixtures and better approximate the biological mode
of action. Further, due to preconceptional enrollment of
women and the pregnancy testing protocol, there is very
little possibility for missed pregnancy losses.
6. Acknowledgements
This research was supported by the Intramural Research
Program of the Eunice Kennedy Shriver National Insti-
tute of Child Health and Human Development, National
Institutes of Health.
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