Preconception blood pressure and time to pregnancy among couples attempting to conceive their first pregnancy

Phthalate exposure and subfecundity in preconception couples: A nested case-control study

BACKGROUND

Phthalates (PAEs) are endocrine-disrupting chemicals ubiquitously found in the environment. This study aimed to examine the association between exposure of PAEs and subfecundity in preconception couples.

METHODS

This is a nested case-control study based on preconception cohort. Preconception couples with intention to conceive were enrolled and followed up until a clinically confirmed pregnancy or 12 menstrual cycles of preparation for conception. A total of 107 couples with subfecundity- time to pregnancy (TTP) more than 12 menstrual cycles, and 144 couples ≤12 cycles were included in the analysis. The levels of PAE metabolites in one spot urine samples were detected and compared between the groups. The weighted quantile sum (WQS) regression model and Bayesian kernel machine regression (BKMR) model were used to examine the joint effects of couples' exposure to PAEs on subfecundity.

RESULTS

Using the multivariate binary logistic regression model, compared to the lowest quartile of urinary ∑PAEs concentration group, both preconception females (aOR=2.42, 95% CI: 1.10-5.30, p=0.027) and males (aOR=2.99, 95% CI: 1.36-6.58, p=0.006) in the highest quartile group had an increased risk of subfecundity, and a dose-response relationship was observed between PAEs and the risk of subfecundity. The WQS analyses found that co-exposure to PAE mixture was a risk factor for subfecundity in preconception female (aOR=1.76, 95% CI: 1.38-2.26, p<0.001), male (aOR=1.58, 95% CI: 1.20-2.08, p=0.001), and couple (aOR=2.39, 95% CI: 1.61-3.52, p<0.001). The BKMR model found a positive combined effect of mixed exposure to PAEs on the risk of subfecundity.

CONCLUSIONS

PAEs increase the risk of subfecundity in preconception couples. Our research reinforced the need of monitoring PAE exposure for the purpose of improving human reproductive health.

Association of maternal preconception blood pressure with preterm birth: a population-based cohort study

The association between maternal preconception blood pressure (BP) and preterm birth (PTB) is still unclear. The purpose of this study was to investigate the association between maternal preconception BP and PTB. This population-based cohort study included 715 984 Chinese women aged 20-49 years who participated in the National Free Preconception Health Examination Project and successfully had a singleton livebirth during 2014-2019 in Guangdong Province, China. Maternal preconception BP were measured by trained health workers. Multivariate logistic regression models and restricted cubic spline regressions were used to examine the association and dose-response relationship between maternal preconception BP and PTB, respectively. Maternal preconception hypertension was associated with the increased risk of PTB (adjusted odds ratios (aOR): 1.24; 95% CI: 1.14-1.34). Compared to women with normal preconception BP, the aORs for PTB were 1.09 (95% CI: 1.06-1.12), 1.24 (95% CI: 1.13-1.36), and 1.43 (95% CI: 1.15-1.79) for women with preconception elevated BP (120-139/ 80-89 mmHg, stage-1 hypertension (140-159/ 90-99 mmHg, and stage-2 hypertension (160-179/100-109 mmHg), respectively. According to the 2017 American College of Cardiology/American Heart Association criteria, maternal preconception elevated BP and hypertension were also significantly associated with an increased risk of PTB. Preconception systolic and diastolic BP showed a U-shaped (χ2 = 40.54; nonlinear P < 0.001) and linear (χ2 = 6.62; nonlinear P = 0.085) dose-response relationship with PTB, respectively. The association was modified by maternal age and preconception body mass index. These findings identify maternal preconception elevated BP and hypertension as a modifiable risk factor for PTB, providing evidence for future research studies, public health and clinical interventions.

Gravidity modifies the associations of age and spousal age difference with couple's fecundability: a large cohort study from China

STUDY QUESTION

Do couple's age ranges for optimal fecundability, and the associations with fecundability of couple's age combinations and age differences differ with gravidity?

SUMMARY ANSWER

The couple's age range of optimal fecundability and age combinations differed with gravidity, and gravidity might modify the associations of age and spousal age difference with couple's fecundability.

WHAT IS KNOWN ALREADY

Age is one of the strongest determinants of fecundability, but the existing studies have certain limitations in study population, couple's extreme age combinations and age differences, and have not explored whether the association between age and fecundability differs with gravidity.

STUDY DESIGN, SIZE, DURATION

Retrospective cohort study. 5 407 499 general reproductive-aged couples (not diagnosed with infertility) participated in the National Free Pre-conception Check-up Projects during 2015-2017. They were followed up for pregnancy outcomes through telephone interviews every 3 months until they became pregnant or were followed up for 1 year.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The main outcome was time to pregnancy, and the fecundability odds ratios and 95% CIs were estimated using the Cox models for discrete survival time. The associations of age and spousal age difference with fecundability were evaluated by restricted cubic splines.

MAIN RESULTS AND THE ROLE OF CHANCE

In this large cohort of general reproductive-aged population, the age of optimal fecundability of multigravida couples was older than that of nulligravida couples, but their subsequent fecundability declined more sharply with age. The decline in female fecundability was more pronounced with age, with fecundability dropping by ∼30% in both nulligravida and multigravida couples whose female partners aged ≥35 years. In the nulligravida group, the fecundability of couples who were both ≤24 years with the same age was the highest, which decreased steadily with the increase of spousal age difference, and younger male partners did not seem to contribute to improving couple's fecundability. In the multigravida group, couples with female partners aged 25-34 years and a spousal age difference of -5 to 5 years showed higher fecundability, and the effect of spousal age difference on couple's fecundability became suddenly apparent when female partners aged around 40 years. Young male partners were unable to change the decisive effect of female partner's age over 40 years on couple's reduced fecundability, regardless of gravidity.

LIMITATIONS, REASONS FOR CAUTION

Lacking the time for couples to attempt pregnancy before enrollment, and some couples might suspend pregnancy plans during follow-up because of certain emergencies, which would misestimate the fecundability. Due to the lack of information on sperm quality and sexual frequency of couples, we could not adjust for these factors. Moreover, due to population characteristics, the extrapolation of our results required caution.

WIDER IMPLICATIONS OF THE FINDINGS

The couple's age range of optimal fecundability, age combinations, and spousal age difference on fecundability varied with gravidity. Female age-related decline in fecundability was more dominant in couple's fecundability. Targeted fertility guidance should be provided to couples with different age combinations and gravidities.

STUDY FUNDING/COMPETING INTEREST(S)

This research received funding from the Project of National Research Institute for Family Planning (Grant No. 2018NRIFPJ03), the National Key Research and Development Program of China (Grant No. 2016YFC1000307), and the National Human Genetic Resources Sharing Service Platform (Grant No. 2005DKA21300), People's Republic of China. The funders had no role in study design, analysis, decision to publish, or preparation of the manuscript. The authors report no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Assessment of Prior Infection With Hepatitis B Virus and Fecundability in Couples Planning Pregnancy

IMPORTANCE

The association of hepatitis B virus (HBV) infection with reduced fecundability among reproductive-aged couples lacks large-population, in-depth study evidence.

OBJECTIVE

To investigate the association of HBV infection with time to pregnancy in couples planning pregnancy, and to explore whether this association varied by gravidity, health statuses, or lifestyles.

DESIGN, SETTING, AND PARTICIPANTS

This is a population-based cohort study of Chinese couples participating in the National Free Preconception Check-up Projects during 2015 to 2017. They were planning pregnancy and were followed-up every 3 months until getting pregnant, as confirmed by gynecologic ultrasonography, or were followed-up for 1 year. Data were analyzed between March 1, 2022, and September 30, 2022.

MAIN OUTCOMES AND MEASURES

The main outcome was time to pregnancy, assessed using fecundability hazard ratios (HRs). The Cox proportional hazards regression models were used to estimate the association of HBV infection with fecundability.

RESULTS

Among 2 419 848 couples (mean [SD] age, 27.87 [5.20] years for women and 29.58 [5.50] years for men), 126 728 women (5.24%) and 156 572 men (6.47%) were infected with HBV. Compared with the HBV-negative group, the fecundability of both women and men in the HBV-positive group decreased by 5% (HR, 0.95; 95% CI, 0.94-0.95). Compared with couples in which both partners were HBV negative, the fecundability of those in which both partners were HBV positive declined by 6% (HR, 0.94; 95% CI, 0.93-0.96) among all couples, by 3% (HR, 0.97; 95% CI, 0.95-0.99) among nulligravidas couples, and by 7% (HR, 0.93; 95% CI, 0.91-0.95) among multigravidas couples. Both the female-male and couple models suggested that the association of HBV infection with decreased fecundability was more pronounced in couples with multigravidas. The negative association was greater in people with overweight and obesity and was inconsistent in certain subgroups; in particular, it was more pronounced in women with reproductive tract infections, normal fasting plasma glucose, and no alcohol intake and in men with normal blood pressure.

CONCLUSIONS AND RELEVANCE

In this population-based cohort study, HBV infection was associated with decreased fecundability in a general reproductive-aged population, especially in couples with multigravidas. For women and men with certain health statuses and lifestyles, a comprehensive consideration of this association is recommended to provide personalized fertility guidance.

Preconception exposure to perfluoroalkyl and polyfluoroalkyl substances and couple fecundity: A couple-based exploration

Numerous studies have examined the adverse health effects of perfluoroalkyl and polyfluoroalkyl substances (PFAS) but it remains unclear whether preconception exposure to PFAS affects couple fecundity. This prospective preconception cohort study with 936 Chinese couples aimed to comprehensively assess the effects of PFAS on couple fecundity [measured by the time to pregnancy (TTP)] and infertility (i.e., TTP > 12 menstrual cycles) with a focus on the effects of partner-specific exposure and joint-effects of couple-based exposure. Twenty-five PFAS were quantified in plasma from each partner, including seven branched isomers, two chlorinated polyfluoroalkyl ether sulfonic acids, four emerging PFAS replacements [i.e., 6:2 fluorotelomer phosphate diester (6:2 diPAP) and three short-chain alternatives: perfluoro-n-butanoicacid, perfluorobutane sulfonate and perfluoroheptanoic acid (PFHpA)]. Using a two-phase regression approach composed of elastic net regression and principal component analysis, we found that exposure to 6:2 diPAP and PFHpA rather than legacy PFAS in women and the couple-based exposure patterns characterized by high level of female 6:2 diPAP were significantly associated with reduced couple fecundity, which was independent of the adjustment of co-exposed PFAS homogenous from both partners. For example, a ln unit increase in female 6:2 diPAP was associated with 15 % [fecundity odds ratio (FOR) = 0.85, 95 %CI: 0.76, 0.96)] lower odds of couple fecundability (i.e., longer TTP) and 45 % increased risk of infertility [OR = 1.45 (95 %CI: 1.16, 1.81)], respectively. While most PFAS in men were not associated with couple fecundity, certain PFAS (e.g., perfluorohexane sulfonic acid) in men were negatively associated with infertility risk. However, the combined effects of PFAS mixture in couples were nonsignificant. Our findings suggest that PFAS in men and women may exert different impacts on couple fecundity. Preconception exposure to 6:2 diPAP and PFHpA in women may have the potential to impair couple fecundity.

Female fecundability is associated with pre-pregnancy allostatic load: Analysis of a Chinese cohort

INTRODUCTION

Allostatic load (AL) is a practical index that reflects multi-system physiological changes which occur in response to chronic psychosocial stress. This study investigated the association between female pre-pregnancy allostatic load and time to pregnancy.

MATERIAL AND METHODS

We enrolled 444 women who met the inclusion criteria and were attempting to achieve pregnancy. Their allostatic load scores at baseline were evaluated by nine indicators (systolic blood pressure, diastolic blood pressure, fasting plasma glucose, plasma cortisol, noradrenaline, interleukin-6, hypersensitive C-reactive protein, high density lipoprotein cholesterol and body mass index). The participants were followed up and their pregnancy outcome ascertained 1 year later; we then calculated time-to-pregnancy. Cox models were used to estimate fecundability ratios and their 95% confidence intervals (95% CI) for different allostatic load scores.

RESULTS

The median allostatic load score was 1 with a range of 0-6. The females were divided into four groups according to allostatic load score: group A (allostatic load = 0, 150/444, 33.8%), group B (allostatic load = 1-2, 156/444, 35.1%), group C (allostatic load = 3-4, 100/444, 22.5%) and group D (allostatic load = 5-6, 38/444, 8.6%). The cumulative pregnancy rate over 12 months for the four groups (A-D) was 55.4%, 44.5%, 50.9% and 26.9%, respectively (log-rank test, p = 0.042). After adjusting for potential confounding factors, group D showed a 59% reduction of fecundability compared with group A (fecundability ratio = 0.41, 95% CI 0.21-0.83).

CONCLUSIONS

Women with a higher allostatic load score may have lower fecundability. Our findings suggest that the assessment of allostatic load during pre-conception consultation would be highly prudent.

Association of Preconception Thyrotropin Levels With Fecundability and Risk of Spontaneous Abortion in China

IMPORTANCE

Abundant evidence suggests thyroid dysfunction is associated with adverse pregnancy outcomes. However, associations of preconception thyrotropin levels outside of reference range with reproductive health outcomes are not well characterized.

OBJECTIVE

To evaluate the associations of preconception thyrotropin levels with time to pregnancy (TTP) and risk of spontaneous abortion (SA).

DESIGN, SETTING, AND PARTICIPANTS

This population-based cohort study used data from the Chinese National Free Prepregnancy Checkups Project. Female participants aged 20 to 49 years who were trying to conceive were enrolled between January 1, 2013, and December 31, 2016, for the analysis of TTP or SA. Data were analyzed between August 1, 2020, and July 5, 2021.

EXPOSURES

Levels of thyrotropin within 1 year prior to pregnancy.

MAIN OUTCOMES AND MEASURES

The main outcomes were TTP, assessed using hazard ratios (HRs), and SA, assessed using odds ratios (ORs), according to preconception thyrotropin levels. Thyrotropin dose-response associations were assessed using restricted cubic spline regression.

RESULTS

Among 11 194 002 female participants (mean [SD] age, 27.56 [5.10] years) in the TTP cohort, 4 739 421 (42.34%) participants became pregnant within 1 year. Both low and high preconception thyrotropin levels were associated with delayed TTP compared with thyrotropin levels of 0.37 to 2.49 mIU/L (thyrotropin <0.10 mIU/L: HR, 0.90; 95% CI, 0.89-0.92; thyrotropin 4.88-9.99 mIU/L: HR, 0.86; 95% CI, 0.86-0.87; thyrotropin ≥10.00 mIU/L: HR, 0.78; 95% CI, 0.77-0.79). In the SA analysis cohort including 4 678 679 pregnancies, 108 064 SA events (2.31%) were documented. High thyrotropin groups showed an increased risk of SA compared with the group with thyrotropin levels of 0.37 to 2.49 mIU/L (thyrotropin 4.88-9.99 mIU/L: OR, 1.33; 95% CI, 1.28-1.38; thyrotropin ≥10.00 mIU/L: OR, 1.25; 95% CI, 1.14-1.36). Preconception thyrotropin levels showed an inverted J-shaped dose-response association with TTP (χ2 = 311.29; nonlinear P < .001) and a J-shaped dose-response association with SA (χ2 = 58.29; nonlinear P < .001).

CONCLUSIONS AND RELEVANCE

In this cohort study, preconception thyrotropin levels outside of reference range were associated with increased risk of reduced fecundity and SA. These findings may provide insights for the implementation of preconception thyroid function screening and the design of future levothyroxine supplementation trials.

The current situation and future directions for the study on time-to-pregnancy: a scoping review

Introduction

As problems associated with infertility and population aging increase, there is a growing interest in the factors that cause a decline in human fertility. Time-to-pregnancy (TTP) is a good indicator with which to reflect human fecundability. Here, we present a comprehensive overview of this topic.

Methods

Relevant qualitative and quantitative studies were identified by searching the Web of science and PubMed electronic databases. We included all literature, written in English, from inception to the 10th April 2021 providing the focus was on TTP. We conducted a narrative synthesis using thematic analysis.

Results

Traditional TTP-related study protocols include prospective and retrospective cohorts that provide a wealth of data to reveal potential influences on TTP. Thus far, a variety of factors have been shown to be associated with TTP in couples preparing for pregnancy, including basic demographic characteristics, menstrual status, chronic disease status, environmental endocrine disruptor exposure, and lifestyles. However, there are inevitable epidemiological bias in the existing studies, including recall bias, selection bias and measurement bias. Some methodological advances have brought new opportunities to TTP research, which make it possible to develop precision interventions for population fertility. Future TTP studies should take advantage of artificial intelligence, machine learning, and high-throughput sequencing technologies, and apply medical big data to fully consider and avoid possible bias in the design.

Conclusion

There are many opportunities and future challenges for TTP related studies which would provide a scientific basis for the “precise health management” of the population preparing for pregnancy.

As the problems of infertility and population aging increase, there is a growing interest in the factors that cause a decline in human fertility. Time-to-pregnancy (TTP) is a good indicator with which to reflect human fecundability, and a longer TTP is known to reflect a reduction in fertility. Many original studies, with different designs, have used TTP to explore the factors that might influence fertility, including basic demographic characteristics, chronic disease status, environmental endocrine disruptor exposure, and lifestyles. However, much of the existing evidence is inconsistent and limited by various types of bias. This review provides a synopsis of recent TTP studies, and highlights new opportunities and future challenges.

Retinal microvasculature and time to pregnancy in a multi-ethnic pre-conception cohort in Singapore

STUDY QUESTION

Can abnormalities in retinal microvasculature representing adverse microcirculatory perfusion and inflammation shed light on the pathophysiology of female fecundability?

SUMMARY ANSWER

In our prospective study, abnormalities in retinal vascular geometric morphology (i.e. sparser arteriolar fractal and larger venular bifurcation) during pre-conception phase are temporarily associated with a prolonged time-to-pregnancy (TTP).

WHAT IS KNOWN ALREADY

Suboptimal retinal microcirculatory morphology has been associated with obesity, psychological stress and hypertension, all of which are known risk factors for reduced female fecundability.

STUDY DESIGN, SIZE, DURATION

A total of 652 women of Chinese, Malay or Indian ethnicity 18-45 years of age and planning to conceive spontaneously within the next 12 months were recruited during the pre-conception period into the Singapore PREconception Study of long-Term maternal and child Outcomes (S-PRESTO), from February 2015 to October 2017.

PARTICIPANTS/MATERIALS, SETTING, METHODS

During recruitment, we collected information on socio-demographic factors, menstrual characteristics and lifestyle behaviors and made anthropometric measurements. We assessed the following retinal microvascular features: caliber, branching angle and fractal dimension. We conducted follow-up telephone surveys to track each participant's pregnancy status at 6, 9 and 12 months after enrolment. We ascertained clinical pregnancies via ultrasonography, with TTP measured by the number of menstrual cycles required to achieve a clinical pregnancy over a 1-year follow-up. Then, we performed discrete-time proportional hazards models to estimate the fecundability odds ratio (FOR) and 95% CI for each retinal microvascular feature in association with TTP, after adjusting for major confounders, including body mass index and fasting glycemic level at study entry.

MAIN RESULTS AND THE ROLE OF THE CHANCE

Among 652 recruited women, 276 (42.3%) successfully conceived within 1 year of follow-up. The mean (and SD) was 1.24 (0.05) Df for retinal arteriolar dimension fraction and 78.45 (9.79) degrees for retinal venular branching angle, respectively. Non-linear relationship testing was performed before multiple adjustment in all associations and a non-monotonic association was detected between retinal venular branching angle and TTP. Compared with women in the highest tertile of retinal arteriolar fractal dimension, women in the second tertile had a prolonged TTP (FOR: 0.68; 95% CI: 0.51-0.92), as did women in the lowest tertile (FOR: 0.73; 95% CI: 0.55-0.98). Compared with women in the middle tertile of retinal venular branching angle, women in the highest tertile had a borderline prolonged TTP (FOR: 0.75; 95% CI: 0.56-1.02). No other retinal vascular features were significantly associated with TTP.

LIMITATIONS, REASONS FOR CAUTION

We were unable to adjust for other potential confounding factors such as female sexual function (e.g. frequency of sexual intercourse), which might introduce a residual bias. Moreover, even though this is a prospective cohort design, our findings can identify the temporal relationship but not necessarily infer a causal relationship between maternal microvasculature and TTP. Lastly, our study involving mainly Chinese, Malay and Indian ethnicities might not be generalizable to other races or ethnicities.

WIDER IMPLICATIONS OF THE FINDINGS

Suboptimal microcirculation may lead to reduced female fecundability. In the future, in addition to conventional ultrasonographic evaluation of ovarian and uterine physiological function, assessing the retinal microvasculature might be useful for assessment of ovarian age, fertility prediction and endometrial evaluation before assisted reproductive techniques for fertility treatments.

STUDY FUNDING/COMPETING INTEREST(S)

This research is supported by the Singapore National Research Foundation (NRF) under its Translational and Clinical Research (TCR) Flagship Programme and administered by the Singapore Ministry of Health's National Medical Research Council (NMRC) (Singapore-NMRC/TCR/004-NUS/2008; NMRC/TCR/012-NUHS/2014) and Singapore National Medical Research Council Transition Award (NMRC TA/0027/2014). The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov, NCT03531658.

The association between vaginal microbiota and female infertility: a systematic review and meta-analysis

PURPOSE

This study aimed to explore the association between vaginal microbiota and infertility.

METHODS

We searched a range of electronic databases for appropriate articles, including PubMed, Web of Science, Embase, Chinese National Knowledge Infrastructure (CNKI), and Wanfang, from inception to 8th September 2019. Identified articles were then screened using strict inclusion and exclusion criteria. By referring to Tamarelle's method, we divided vaginal microbiota into two categories: low-Lactobacillus vaginal microbiota (LL-VMB) and high-Lactobacillus vaginal microbiota (HL-VMB). Patients were defined as HL-VMB if they had a Nugent score of 0-3, a negative Amesel/Spiegel's test, or if the vaginal community status was dominated by either L. crispatus, L. iners, L. gasseri and L. jensenii via 16S rRNA sequencing. Otherwise, cases were regarded as LL-VMB. Statistical analyses were performed with STATA 13.0 statistical software. Effect estimates are presented as odds ratios (ORs) with 95% confidence intervals (CIs).

RESULTS

Fifteen articles were included in our final analysis. The HL-VMB was negatively related to infertility; a fixed model showed that the pooled OR was 0.83 (95% CI 0.77-0.90). There was no significant publication bias, as determined by Begg's test (P = 0.488) and Egger's test (P = 0.652). Using a random effect model, the pooled OR for intermediate bacterial vaginitis (BV) and infertility was 1.39 (95% CI 1.10-1.76) and the pooled OR for positive BV was 1.72 (95% CI 1.10-2.69). Subgroup and sensitivity analyses further demonstrated that the associations identified were stable. However, the acquired evidence was not sufficient to make inferences with regards to the mechanisms underlying these relationships.

CONCLUSION

This systematic review and meta-analysis identified a negative correlation between HL-VMB and female infertility. However, due to a variety of limitations, the evidence acquired does not allow us to identify the specific mechanisms underlying this association. Further high-quality studies are needed to verify the causal relationship and explore the molecular mechanisms involved.