Effect of ambient air pollutants on in vitro fertilization-embryo transfer pregnancy outcome in Zhengzhou, China

Association of ambient air pollutant mixtures with IVF/ICSI-ET clinical pregnancy rates during critical exposure periods

STUDY QUESTION

Does exposure to a mixture of ambient air pollutants during specific exposure periods influence clinical pregnancy rates in women undergoing IVF/ICSI-embryo transfer (ET) cycles?

SUMMARY ANSWER

The specific exposure period from ET to the serum hCG test was identified as a critical exposure window as exposure to sulfur dioxide (SO2) or a combination of air pollutants was associated with a decreased likelihood of clinical pregnancy.

WHAT IS KNOWN ALREADY

Exposure to a single pollutant may impact pregnancy outcomes in women undergoing ART. However, in daily life, individuals often encounter mixed pollution, and limited research exists on the effects of mixed air pollutants and the specific exposure periods.

STUDY DESIGN SIZE DURATION

This retrospective cohort study involved infertile patients who underwent their initial IVF/ICSI-ET cycle at an assisted reproduction center between January 2020 and January 2023. Exclusions were applied for patients meeting specific criteria, such as no fresh ET, incomplete clinical and address information, residency outside the 17 cities in the Sichuan Basin, age over 45 years, use of donor semen, thin endometrium (<8 mm) and infertility factors unrelated to tubal or ovulation issues. In total, 5208 individuals were included in the study.

PARTICIPANTS/MATERIALS SETTING METHODS

Daily average levels of six air pollutants (fine particulate matter (PM2.5), inhalable particulate matter (PM10), SO2, nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3)) were acquired from air quality monitoring stations. The cumulative average levels of various pollutants were determined using the inverse distance weighting (IDW) method across four distinct exposure periods (Period 1: 90 days before oocyte retrieval; Period 2: oocyte retrieval to ET; Period 3: ET to serum hCG test; Period 4: 90 days before oocyte retrieval to serum hCG test). Single-pollutant logistic regression, two-pollutant logistic regression, Quantile g-computation (QG-C) regression, and Bayesian kernel machine regression (BKMR) were employed to evaluate the influence of pollutants on clinical pregnancy rates. Stratified analyses were executed to discern potentially vulnerable populations.

MAIN RESULTS AND THE ROLE OF CHANCE

The clinical pregnancy rate for participants during the study period was 54.53%. Single-pollutant logistic models indicated that for PM2.5 during specific exposure Period 1 (adjusted odds ratio [aOR] = 0.83, 95% CI: 0.70-0.99) and specific exposure Period 4 (aOR = 0.83, 95% CI: 0.69-0.98), and SO2 in specific exposure Period 3 (aOR = 0.92, 95% CI: 0.86-0.99), each interquartile range (IQR) increment exhibited an association with a decreased probability of clinical pregnancy. Consistent results were observed with dual air pollution models. In the multi-pollution analysis, QG-C indicated a 12% reduction in clinical pregnancy rates per IQR increment of mixed pollutants during specific exposure Period 3 (aOR = 0.89, 95% CI: 0.79-0.99). Among these pollutants, SO2 (33.40%) and NO2 (33.40%) contributed the most to the negative effects. The results from BKMR and QG-C were consistent. Stratified analysis revealed increased susceptibility to ambient air pollution among individuals who underwent transfer of two embryos, those with BMI ≥ 24 kg/m2 and those under 35 years old.

LIMITATIONS REASONS FOR CAUTION

Caution was advised in interpreting the results due to the retrospective nature of the study, which was prone to selection bias from non-random sampling. Smoking and alcohol, known confounding factors in IVF/ICSI-ET, were not accounted for. Only successful cycles that reached the hCG test were included, excluding a few patients who did not reach the ET stage. While IDW was used to estimate pollutant concentrations at residential addresses, data on participants' work locations and activity patterns were not collected, potentially affecting the accuracy of exposure prediction.

WIDER IMPLICATIONS OF THE FINDINGS

Exposure to a mixture of pollutants, spanning from ET to the serum hCG test (Period 3), appeared to be correlated with a diminished probability of achieving clinical pregnancy. This association suggested a potential impact of mixed pollutants on the interaction between embryos and the endometrium, as well as embryo implantation during this critical stage, potentially contributing to clinical pregnancy failure. This underscored the importance of providing women undergoing ART with comprehensive information to comprehend the potential environmental influences and motivating them to adopt suitable protective measures when feasible, thereby mitigating potential adverse effects of contaminants on reproductive health.

STUDY FUNDING/COMPETING INTERESTS

This work received support from the National Key Research and Development Program of China (No. 2023YFC2705900), the National Natural Science Foundation of China (Nos. 82171664, 81971391, 82171668), the Natural Science Foundation of Chongqing Municipality of China (Nos. CSTB2022NSCQ-LZX0062, CSTB2023TIAD-KPX0052) and the Foundation of State Key Laboratory of Ultrasound in Medicine and Engineering (No. 2021KFKT013). The authors report no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Air pollution and fecundability in a North American preconception cohort study

BACKGROUND

Animal and epidemiologic studies indicate that air pollution may adversely affect fertility. However, the level of evidence is limited and specific pollutants driving the association are inconsistent across studies.

METHODS

We used data from a web-based preconception cohort study of pregnancy planners enrolled during 2013-2019 (Pregnancy Study Online; PRESTO). Eligible participants self-identified as female, were aged 21-45 years, resided in the United States (U.S.) or Canada, and were trying to conceive without fertility treatments. Participants completed a baseline questionnaire and bi-monthly follow-up questionnaires until conception or 12 months. We analyzed data from 8,747 participants (U.S.: 7,304; Canada: 1,443) who had been trying to conceive for < 12 cycles at enrollment. We estimated residential ambient concentrations of particulate matter < 2.5 µm (PM2.5), nitrogen dioxide (NO2), and ozone (O3) using validated spatiotemporal models specific to each country. We fit country-specific proportional probabilities regression models to estimate the association between annual average, menstrual cycle-specific, and preconception average pollutant concentrations with fecundability, the per-cycle probability of conception. We calculated fecundability ratios (FRs) and 95% confidence intervals (CIs) and adjusted for individual- and neighborhood-level confounders.

RESULTS

In the U.S., the FRs for a 5-µg/m3 increase in annual average, cycle-specific, and preconception average PM2.5 concentrations were 0.94 (95% CI: 0.83, 1.08), 1.00 (95% CI: 0.93, 1.07), and 1.00 (95% CI: 0.93, 1.09), respectively. In Canada, the corresponding FRs were 0.92 (95% CI: 0.74, 1.16), 0.97 (95% CI: 0.87, 1.09), and 0.94 (95% CI: 0.80, 1.09), respectively. Likewise, NO2 and O3 concentrations were not strongly associated with fecundability in either country.

CONCLUSIONS

Neither annual average, menstrual cycle-specific, nor preconception average exposure to ambient PM2.5, NO2, and O3 were appreciably associated with reduced fecundability in this cohort of pregnancy planners.

Does exposure to air pollution during different time windows affect pregnancy outcomes of in vitro fertilization treatment? A systematic review and meta-analysis

Few researches have examined the impact of air pollution exposure during various time windows on clinical outcomes in women receiving in vitro fertilization (IVF) therapy, and the findings of studies have been conflicting. We investigated the effects of six air pollutants exposure during different time windows (period 1, 85 days before egg retrieval to the beginning of gonadotropin; period 2, the beginning of gonadotropin to egg collection; period 3, egg collection to embryo transfer; period 4, embryo transfer to serum hCG measurement; period 5, serum hCG measurement to transvaginal ultrasonography; period 6, 85 days before egg retrieval to hCG measurement; period 7, 85 days before egg retrieval to transvaginal ultrasonography) on clinical outcomes of IVF therapy. A total of seven databases were searched. NO₂ (period 6), SO₂ (period 2, 3, and 7), CO (period 1, 2 and 7) exposure were linked to lower likelihoods of clinical pregnancy. PM_2.5 (period 1), PM₁₀ (period 1), SO₂ (period 1, 2, 3, 4, and 6), NO₂ (period 1) were linked to lower likelihoods of biochemical pregnancy. PM_2.5 (period 1), SO₂ (period 2 and 4) and CO (period 2) were linked to reduced probabilities of live birth. Our results implied that period 1 might be the most sensitive exposure window. Air pollution exposure is linked to reduced probabilities of clinical pregnancy, biochemical pregnancy, and live birth. Therefore, preventive measures to limit air pollution exposure should be started at least three months in advance of IVF therapy to improve pregnancy outcomes.

The impact of air pollution and endocrine disruptors on reproduction and assisted reproduction

PURPOSE OF REVIEW

Rapid increase in world population accompanied by global industrialization has led to an increase in deployment of natural resources, resulting in growing levels of pollution. Here, we review recent literature on the impact of environmental pollution on human reproductive health and assisted reproduction outcomes, focusing on two of the most common: air pollution and endocrine disruptors.

RECENT FINDINGS

Air pollution has been associated with diminished ovarian reserve, uterine leiomyoma, decreased sperm concentration and motility. Air pollution also correlates with decreased pregnancy rates in patients undergoing infertility treatment using in-vitro fertilization (IVF). Similarly, Bisphenol A (BPA), a well studied endocrine disrupting chemical, with oestrogen-like activity, is associated with diminished ovarian reserve, and abnormal semen parameters, while clinical implications for patients undergoing infertility treatment remain to be established.

SUMMARY

There is convincing evidence that environmental pollutants may have a negative impact on human health and reproductive potential. Air pollutions and endocrine disrupting chemicals found in water and food seem to affect male and female reproductive function. Large-scale studies are needed to determine the threshold values for health impact that may drive targeted policies.

Effects of air pollution on clinical pregnancy rates after in vitro fertilisation (IVF): a retrospective cohort study

OBJECTIVE

To evaluate the effect of air pollution, from oocyte retrieval to embryo transfer, on the results of in vitro fertilisation (IVF) in terms of clinical pregnancy rates, at two fertility centres, from 2013 to 2019.

DESIGN

Exploratory retrospective cohort study.

SETTING

This retrospective cohort study was performed in the Reproductive Biology Department of Bordeaux University Hospital localised in Bordeaux, France and the Jean Villar Fertility Center localised in Bruges, France.

PARTICIPANTS

This study included 10 763 IVF attempts occurring between January 2013 and December 2019, 2194 of which resulted in a clinical pregnancy.

PRIMARY AND SECONDARY OUTCOME MEASURES

The outcome of the IVF attempt was recorded as the presence or absence of a clinical pregnancy; exposure to air pollution was assessed by calculating the cumulative exposure of suspended particulate matter, fine particulate matter, black carbon, nitrogen dioxide and ozone (O₃₎, over the period from oocyte retrieval to embryo transfer, together with secondary exposure due to the presence of the biomass boiler room, which was installed in 2016, close to the Bordeaux University Hospital laboratory. The association between air pollution and IVF outcome was evaluated by a random-effects logistic regression analysis.

RESULTS

We found negative associations between cumulative O₃ exposure and clinical pregnancy rate (OR=0.92, 95% CI = (0.86 to 0.98)), and between biomass boiler room exposure and clinical pregnancy rate (OR=0.75, 95% CI = (0.61 to 0.91)), after adjustment for potential confounders.

CONCLUSION

Air pollution could have a negative effect on assisted reproductive technology results and therefore precautions should be taken to minimise the impact of outdoor air on embryo culture.