Phthalate exposure ups risk of pregnancy loss in Chinese women
Higher urinary concentrations of monoethyl phthalate (MEP), high molecular weight phthalate (HMWP) metabolites, and other phthalate metabolites, increase the risk of pregnancy loss in pregnant Chinese women, a new study has found.
“Our findings suggested that Chinese women who were exposed to phthalates during early pregnancy had an increased risk of clinical pregnancy loss, especially embryonic loss,” researchers said.
Concentrations of phthalate metabolites were measured from urine samples of 3,111 pregnant women. Those with ectopic pregnancies, stillbirths, therapeutic abortions or multiple gestations were excluded from the study.
Aside from MEP and HMWP metabolites, urinary levels of monomethyl phthalate, monobutyl phthalate (MBP), monobenzyl phthalate, mono (2-ethylhexyl) phthalate, mono (2-ethyl-5-oxohexyl) phthalate (MEOHP), mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) and low molecular weight phthalate (LMWP) metabolites were also measured.
Logistic regression analysis showed that a higher risk of clinical pregnancy loss was significantly associated with higher levels of MEP (odds ratio [OR], 1.62; 95 percent CI, 0.98 to 2.69), MBP (OR, 1.59; 1.00 to 2.56), MEOHP (OR, 1.70; 1.05 to 2.74), MEHHP (OR, 2.26; 1.35 to 3.78), LMWP (OR, 1.60; 1.00 to 2.60) and HMWP (OR, 1.74; 1.08 to 2.80) after adjusting for education, parity, maternal age and gestational weeks. [Sci Rep 2017;7:6800]
Similarly, the risk of embryonic loss was associated with higher concentrations of MEP (OR, 1.65; 0.84 to 3.23), MEOHP (OR, 2.16; 1.13 to 4.11), MEHHP (OR, 2.19; 1.12 to 4.28) and HMWP (OR, 2.19; 1.15 to 4.17). In contrast, the risk of foetal loss was associated only with higher MEHHP levels (OR, 2.41; 1.10 to 5.30).
The current literature has been conflicted about the extent of the relationship between exposures to different types of phthalates with pregnancy loss, researchers said. [Environ Health Perspect 2012; 120:458-463; Epidemiology 2016; 27:879-888]
“We hypothesized that the discrepancy between the present study and the previous studies was attributed partially to the differences in maternal characteristics, study design, sample size and miscarriage type and partially to co-linearity among phthalate metabolites,” they continued.
The current study showed that embryonic loss was sensitive to phthalate exposure possibly because phthalates interfere with oestradiol and progesterone production in the ovaries, the investigators explained.
“Their adverse effects on endocrine functioning is likely to change the circulating levels of hormones responsible for maintaining pregnancy.”
The study has some important limitations. One is the unusually low proportion of pregnancy loss in the study sample which may be explained by the higher socioeconomic status of the participants in general. Use of a single-spot urine sample for measuring phthalate concentration is another weakness.
Regardless, the study has shown that exposure to phthalates during pregnancy, measured through urinary phthalate levels, is a risk factor for pregnancy loss in Chinese women. Future studies are needed to verify these findings.