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Cohort Profile: Preconception Reproductive Health and Birth Outcome Cohort (PREBIC) in Chongqing, China

Year: 2025

Type: article

Abstract: The Preconception Reproductive Health and Birth Outcome Cohort (PREBIC) is an ongoing, general-population-based birth cohort aiming for a size of 20 000 couples (40 000 individual parents), focusing on both paternal and maternal influences on offspring. It was established on the groundwork of a nationwide free preconception examination service initiated by China government, which benefits the cohort with standardized recruitment and follow-ups. The cohort started recruiting on 28 October 2018 from couples trying to conceive and follow-up continued until their offspring reached the age of 2 years (covering the first 1000 days of life) or until the couple had failed to achieve pregnancy within 2 years. Both potential parents were included and semen samples were collected at baseline, which allows evaluation of the influences from each of the parents since preconception. At the time of writing, the cohort included >17 800 participants who are being actively followed up. All data were collected by a team of trained technicians or via standard clinical procedures. Cooperation with Ji'nan University and BGI Genomics allows exposomic assessment and genomic sequencing to be carried out. The cohort welcomes collaboration. Proposals from other researchers about using the cohort data may be addressed to Dr Cao (e-mail: [email protected]). In a 1986 report, Barker proposed the ‘fetal origins hypothesis’ that environmental factors during the fetal stage can affect future life [1, 2]. The more recent concept of ‘DOHaD’ (Development Origins of Health and Disease), which concerns the way in which environmental exposures during the first 1000 days (280 days before birth + ∼730 infantile days after birth) affect health and disease later in life, is now widely accepted [3]. A prospective cohort design is one of the most powerful tools among the methodologies in DOHaD studies. The Northern Finland Birth Cohort was used to assess the prenatal determinants of physical activity and cardiorespiratory fitness in adolescence [4]. Researchers carried out similar studies in non-birth cohorts, such as populations who experienced famine or war in early life [5, 6]. Maternal factors are extensively studied in most birth cohorts, yielding well-recognized and accepted results [7, 8]. However, both parents undoubtedly contribute to pregnancies and developmental health of the offspring [9–12] and animal experiments prove that preconceptional paternal exposures may lead to adverse outcomes [13]. Despite this, few population-based studies have explored the effects of paternal exposures on offspring. The Chinese government funds Health Centres for Women and Children, which provide free preconception care services to couples who are trying to conceive [14]. For each conception attempt, this service offers both the wife and the husband with a set of pre-gestational medical examinations. Taking advantage of this service, the Preconception Reproductive Health and Birth Outcome Cohort (PREBIC) was established and has been recruiting couples of childbearing aged who are trying to conceive. This cohort emphasizes the collection of information on preconceptional exposures, so the baseline was set as prior to a conception and both potential parents were recruited simultaneously (Figure 1). The PREBIC researchers believe that this cohort will offer special insights into reproduction, gestation, and development. In order to use the cohort data more effectively, PREBIC is registered as a member of the China Cohort Consortium and participates in the Chinese Birth Cohort League, to promote data sharing and cooperation in multicentre studies. Design and flow chart of the cohort and its current progress. PREBIC is managed by the Institute of Toxicology, Army Medical University, and the Women and Children’s Hospital of Chongqing Medical University. This dynamic cohort is still actively recruiting participants. All couples of reproductive ages participating in the free national preconception care service programme in the Department of Health, Women and Children’s Hospital of Chongqing Medical University were invited to join the cohort. A group of trained interviewers guide potential participants through the registration form and the required informed consent to identify eligible participants, who should meet three criteria: (i) to be planning a pregnancy in the next 12 months; (ii) to have lived in Chongqing for >2 years with no plans to leave in the following 2 years; and (iii) be aged 20–49 years for the wife or 22–49 years for the husband (legal marriage ages are 20 and 22 years for women and men in China, respectively). Any of the following criteria results in a participant’s exclusion: (i) diagnosis with genitourinary system diseases, such as infertility, testicular/ovarian dysplasia syndrome, genital injuries, sexually transmitted diseases, mumps after puberty, or heritable diseases; (ii) sterilization; (iii) for men only, a fever of >38.5°C or not having met the 2–7 days of abstinence that is recommended by the World Health Organization (WHO) for assessing semen quality. The required sample size for the cohort was estimated according to the rate of birth defects in Chongqing (∼4% as reported by the government [15], which was the lowest incidence among all adverse outcomes of interest in the cohort and thereby required the largest sample size). By setting the relative risk (RR) detection level at 1.5 and using the model of ‘test for inequality between two independent proportions’ in PASS software (version 2021, Utah, USA), the sample size was estimated at 4160 couples (α = 0.05, β = 0.80, exposed group vs. control group = 1:1). The hospital-based data showed that, in 12 months of unprotected intercourse, ∼50% of couples trying to conceive would fail. Considering a loss to follow-up of 20%, the sample size was determined to be 10 400 couples. Given that new risks continue to emerge and to allow the detection of a lower RR in the future, we set the long-term goal for the sample size at 20 000 couples. Three stages of follow-up (preconception, pregnancy, and offspring) are carried out by a group of trained technicians and interviewers. A telephone or social application interview is conducted to obtain the participants’ clinical records, including outcomes of preparation for pregnancy and pregnancy health. Once the repeated telephone or social application contacts yield no response, we resort to retrieving clinical data from the hospital information system. In the first stage (preconception), both female and male participants are followed up every 3 months after the day they are recruited. This stage is terminated if pregnancy is achieved or if the couple fail to conceive within 2 years. Pregnant women are transferred to the second stage of follow-up (pregnancy), during which there are three separate follow-ups through three trimesters. Women who give birth have an extra follow-up for biopsy sampling at the time of delivery unless there is an emergency that precludes this. Follow-up in the third stage is of the offspring, occurring at 42 days, 6 months, 1 year, and 2 years after birth. Information on relevant physical parameters and preconception medical examinations is collected at baseline. Both male and female participants complete a previously verified online questionnaire on a tablet provided by the interviewer (Table 1); 10 ml of blood and 20 ml of urine are obtained from both male and female participants, and a semen sample is collected from each husband. Characteristics collected by questionnaires. MCTQ, Munich ChronoType Questionnaire; PSQI, Pittsburgh Sleep Quality Index; IPAQ, International Physical Activity Questionnaire; JCQ, Job Content Questionnaire; PSS, Perceived Stress Scale; ART, assisted reproductive technology. Characteristics collected by questionnaires. MCTQ, Munich ChronoType Questionnaire; PSQI, Pittsburgh Sleep Quality Index; IPAQ, International Physical Activity Questionnaire; JCQ, Job Content Questionnaire; PSS, Perceived Stress Scale; ART, assisted reproductive technology. Stage 1 follow-up collects information via a questionnaire on pregnancy outcomes, including whether and when the pregnancy was achieved, and whether there was a miscarriage (Table 1). No biological samples are collected during Stage 1. Stage 2 follow-up collects data on the physical condition of the participants, socio-psycho-behavioural styles, environmental exposures, and complications of pregnancy (Table 1). This is done via either a telephone interview or a self-reported questionnaire embedded into a Wechat (the most popular social application in China) applet. Information on medical examinations conducted by physicians during pregnancy and medical records on obstetric and birth data are extracted from the hospital information system by the trained researchers. At the time of delivery, maternal blood, umbilical cord blood, six placenta tissue samples (1 × 1 cm per piece; three pieces for the sporophyte side and three for the gametophyte side), and ∼2 cm of umbilical cord are collected if there was no emergency event precluding the sampling. In Stage 3, data on the offspring are collected, including physical parameters (height, weight, head circumference, etc.; measured at each follow-up) and neurological development (via Gesel I, Denver Developmental Screening Test; measured at the follow-ups of 6 months and 1 year after birth). A questionnaire on feeding and nurturing is completed by the parents. For each newborn, three dried blood spots are collected during sampling for universal newborn hearing screening (usually 3 days after birth). A buccal swab is collected at the age of 1 year. All questionnaires and scales used in the PREBIC cohort were previously established for research or clinical purposes [16–19]. For biological samples, complete blood count, urinalysis, serum sex hormone level measurements in women and semen parameters with sperm morphology inspection in men are carried out in the clinical laboratory. A metabolomics study of blood and a urine analysis of inner exposures to environmental pollutants, such as metabolites of phthalic acid esters, polycyclic aromatic hydrocarbons, and emerging organic contaminants, are determined. All biological samples are stored at –80°C or in liquid nitrogen. The ongoing PREBIC study aims at studying the effects of preconception exposures on offspring and more results, including reproductive parameters and birth outcomes, are continuously accumulating. Here, we report some preliminary results obtained in the cohort. The participants were from all 38 districts/counties of Chongqing municipality, which has 32.1 million people in an area of 82 402 km2 [20, 21]. By 31 March 2023, a total of 19 370 potential participants had given informed consent, of whom 1487 were excluded on the basis of our exclusion criteria. This left 17 883 participants (9217 females and 8666 males) who were included, among whom 6561 couples were matched. Among all 8666 males, 7784 semen samples were collected, 5948 from coupled participants. All eligible participants were assigned to Stage 1 of follow-up. Among the 9217 females, 5154 (of whom 3791 were coupled) were recorded as pregnant and 1893 were recorded as delivered. Among all pregnant women, 261 stillbirths, 229 spontaneous, and 99 induced abortions were documented; of these 589 cases, 547 were from coupled participants. At the end of Stage 1 of follow-up, 1379 couples were recorded as infertile (by applying the criterion of failure in pregnancy with unprotected sexual intercourse over 1 year). For the offspring at Stage 3 of follow-up, 1794 questionnaires were collected for infants up to the age of 42 days because some had attended the children’s healthcare clinic more than once during their first 42 days. A total of 611 and 156 questionnaires were collected at the ages of 6 months and 1 year, respectively (Figure 1). The ages of both sexes showed significantly skewed distributions. Most participants were 26–35 years old (77.3% for females and 76.4% for females). Males in age groups of >30 years numbered significantly more than females (P < 0.001). Most participants had a college education or above (73.8% for females, 70.3% for males). Most participants had a college education or above (73.8% for females, 70.3% for males). Males had a significantly higher body mass index (BMI) than females (obese rates were 14.6% for males, 0.3% for females). However, more females had a low BMI (Table 2). Around half of the males consumed tobacco regularly and alcohol occasionally; these proportions were significantly higher for males than females (P < 0.001). The yearly changes in the mean ages of females at baseline increased year by year. Their mean age increased by 0.5 years between 2019 and 2022 (Figure 2) and this increased to 0.7 years between 2022 and 2023 (data from the first 3 months of 2023). Yearly changes in baseline female average age, annual household income, and pregnancy rate. (A) The mean age of females at baseline was increasing yearly compared with 2019; a 0.7-year increase was found in 2023. (B) Families with high income and low income were decreasing, while middle-income families, especially those with 150–800 thousand yuan, were increasing. (C) Pregnancy rates in couples with bearing intention dropped dramatically from 2019 to 2021. Demographics at baseline of current cohort profile. CNY, Chinese yuan renminbi. One subject did not report her ID number and reported a wrong number for her age. Pictures for kinds and volume sizes of various alcoholic beverages (e.g. liquor, wine, beer, etc.) were shown in the questionnaire; the data reported by the volunteers were converted into standard shots (a shot is equivalent to 50 ml of liquor and has 40% alcohol v/v). Demographics at baseline of current cohort profile. CNY, Chinese yuan renminbi. One subject did not report her ID number and reported a wrong number for her age. Pictures for kinds and volume sizes of various alcoholic beverages (e.g. liquor, wine, beer, etc.) were shown in the questionnaire; the data reported by the volunteers were converted into standard shots (a shot is equivalent to 50 ml of liquor and has 40% alcohol v/v). We observed a dramatic decrease in the rate of pregnancies among our cohort of couples who intended to conceive. There was a 64.08% pregnancy rate in 2019, but this had dropped to 46.79% in 2021. Families with middle income levels (80–150 and 150–800 thousand Chinese yuan/year) constitute the largest share of all investigated couples with childbearing intention. The proportions for low-income (≤80 thousand per year) and high-income (≥800 thousand per year) families have decreased year by year since 2020 (Figure 2). The COVID-19 pandemic may have contributed to the change, but we believe that social factors, such as changing opinions about childbearing, were the main factors contributing to this phenomenon. This indicates that further studies are needed. Cambell and colleagues [22] reported semen parameters from men who achieved natural conception within 1 year of unprotected sexual intercourse and their data were adopted by the 6th edition of the WHO laboratory manual for the examination and processing of human semen [23]. Compared with the parameters adopted by the WHO, the population in the PREBIC cohort showed moderate differences in sperm concentration, total sperm count, total motility, progressive motility, and normal morphology. In the lower percentiles of semen parameters, those described above in the PREBIC cohort were better than those from the WHO, while, in the higher percentiles, the situation was reversed, and the intersections were usually observed to be located around the medians, except for normal morphology. For the parameter of normal morphology, the clinical laboratory adopts the criteria from the WHO laboratory manual for the examination and processing of human semen (the 5th edition), which determines 5% of normal morphology of sperm as normal, and thus reports all semen samples that have a higher normal morphology than 5% as ‘normal’. On the criterion of normal morphology, 90% of the males in the PREBIC cohort had <5% sperm with normal morphology—much worse compared with the WHO data (Figure 3). The potential reasons underlying these discrepancies require further studies. Comparison of six semen parameters between the current cohort and the statistics from the WHO laboratory manual for the examination and processing of human semen (sixth edition, 2021). All the numbers in the x-axis represent percentiles. Compared with statistics from the WHO, the results from the current cohort showed milder changes in almost all parameters except semen volume, which are higher in the lower-percentile ends but lower in the other. To our current knowledge, this is the first cohort study with a large sample size (designed to recruit >20 000 couples) aiming to discover preconceptional exposures from both parents that may affect birth outcomes and offspring development. The PREBIC cohort has several strengths that may offer unique chances for discovering evidence, particularly of paternal preconception exposures, that may affect fertility, gestation, birth, and development. First, instead of setting the baseline at initial obstetric examinations, the PREBIC cohort sets the baseline at the time of trying to conceive and follows couples until their offspring are 2 years old. Second, it looks at factors from both parents, with the assessment of semen samples collected from potential fathers at baseline. As far as we know, most current studies focusing on outcomes of pregnancy and offspring do not include semen collection [24–27], except for the population with a treatment of assisted reproductive technologies [28, 29]. Third, the PREBIC cohort was established and is running in the context of a government-initiated national service, which is supportive in recruitment and follow-ups. Fourth, as the biggest municipality in China, Chongqing has 38 districts/counties with distinct characteristics in geographic conditions, economic development, environmental contaminations, and lifestyles, which make it possible to investigate individual and combined impacts of various external exposures on reproductive health and birth outcomes. Fifth, PREBIC is a dynamic cohort, which means that we can adopt more study purposes and accumulate more samples. The main limitation of the PREBIC cohort is that it is an observational study. The design and ethics approval do not permit any intervention research. Thus, it may be difficult to explore causal relationships and the results need validation from other studies. 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Source: International Journal of Epidemiology

DOI: 10.1093/ije/dyaf081