Hong-tian Li

Title：Associate Professor, Doctoral Supervisor

Duty：Dean of Institute of Reproductive and Child Health of Peking University

Email：lihongtian@pku.edu.cn

Address: 38 Xueyuan Rd , Haidian District,Beijing,China

Personal profile

03/2024-Present	Dean of Institute of Reproductive and Child Health of Peking University, Beijing, P. R. China
11/2023-Present	Director of the Office for National Maternal and Child Health Statistics of China, School of Public Health, Peking University, Beijing, P. R. China
08/2017-Present	Associate Professor, Institute of Reproductive and Child Health, Department of Epidemiology and Health Statistics, School of Public Health, Peking University, Beijing, P. R. China
08/2012-07/2016	PhD, Department of Epidemiology and Health Statistics, School of Public Health, Peking University, Beijing, P. R. China
08/2011-07/2017	Assistant Professor, Institute of Reproductive and Child Health, Department of Epidemiology and Health Statistics, School of Public Health, Peking University, Beijing, P. R. China
08/2009-07/2011	Research Assistant, Institute of Reproductive and Child Health, Department of Epidemiology and Health Statistics, School of Public Health, Peking University, Beijing, P. R. China
08/2006-07/2009	MPH, Department of Epidemiology and Health Statistics, School of Public Health, Peking University, Beijing, P. R. China
08/2001-07/2006	MD, Department of Preventive Medicine, North China Coal Medical College, Tangshan, P.R. China

By utilizing multiple epidemiological research methods, my main research focus is to reveal the distribution patterns, risk factors, and prevention and control strategies of the main issues affecting population reproductive health, and to serve for policy making, healthcare service delivery, and development and evaluation of reproductive health related products. I have been the principle or core investigator of several projects funded by the National Natural Science Foundation of China, the National Health Commission of China, and the Ministry of National Science and Technology of China. I have published more than 40 papers in peer-reviewed journals, including JAMA, BMJ, Science Bulletin, and BMC Medicine. I teach "Introduction to SAS", "SAS Multivariate Statistical Analysis", "Epidemiology", "Experimental Epidemiology", and "Health Data Science" for undergraduate and postgraduate students.

Main research directions

Translational and Implementation Research in Reproductive Health

Representative research projects

(1) National Key Research and Development Program, Artificial intelligence monitoring and diagnosis technology and platform construction for common mental diseases, Co-Investigator, 2023-2026

(2) National Health Commission of China, Multi-source data analysis and research on basic characteristics of pregnant women in China, PI, 2021-2022

(3) Clinical Medicine Plus X-Young Scholars Project of Peking University, Study on optimal strategy of clinical pathway for cesarean section during labor, Co-PI, 2022

(4) Clinical Medicine Plus X-Young Scholars Project of Peking University, Development of an auxiliary evaluation system for fetal physical development in twin pregnancy, Co-PI, 2021

(5) National Natural Science Foundation of China, Effect of vaginal seeding on infant body mass index and allergy risk index for caesarean-delivered children: A randomized controlled study, PI, 2018/1-2020/12

(6) National Health Commission of China, Dynamic monitoring of maternal and infant health outcomes, PI, 2021-2022

(7) National Key Research and Development Program, Study on prevention and treatment of complications of pregnancy at an advanced age, Co-Investigator, 2016-2021

10 Representative papers (Note：*Corresponding author, #Co-first author)

(1) Li HT, Tang JL, Qiao J*. China's declining fertility rate. BMJ. 2024;385:q1000.

(2) Yu HZ#, Wang XW#, Guo ZY, Lin Z, Zhou YB, Li HT*, Liu JM*. Association of caesarean delivery with offspring health outcomes in full-cohort versus sibling-comparison studies: a comparative meta-analysis and simulation study. BMC Med. 2023;21(1):348.

(3) Li HT, Hellerstein S, Zhou YB, Liu JM*, Blustein J. Trends in Cesarean Delivery Rates in China, 2008-2018. JAMA. 2020;323(1):89-91.

(4) Li HT#, Xue M#, Hellerstein S, Cai Y, Gao Y, Zhang Y, Qiao J*, Blustein J, Liu JM*. Association of China's universal two child policy with changes in births and birth related health factors: national, descriptive comparative study. BMJ. 2019;366:l4680.

(5) Li HT, Hellerstein S, Kang C, Trasande L, Gao Y, Zhang Y, Luo S, Zhou Y, Qiao J*, Blustein J, Liu JM*. The number of births in China in 2015: policy meets superstition. Science Bulletin. 2018;63(19):1235-1310.

(6) Li HT#, Luo S#, Trasande L, Hellerstein S, Kang C, Li JX, Zhang Y, Liu JM*, Blustein J. Geographic Variations and Temporal Trends in Cesarean Delivery Rates in China, 2008-2014. JAMA. 2017;317(1):69-76.

(7) Li HT, Trasande L, Zhu LP, Ye RW, Zhou YB, Liu JM*. Association of cesarean delivery with anemia in infants and children in 2 large longitudinal Chinese birth cohorts. Am J Clin Nutr. 2015;101(3):523-9.

(8) Li HT, Ye R, Pei L, Ren A, Zheng X, Liu JM*. Caesarean delivery, caesarean delivery on maternal request and childhood overweight: a Chinese birth cohort study of 181380 children. Pediatr Obes. 2014;9(1):10-6.

(9) Li HT, Zhou YB, Liu JM*. The impact of cesarean section on offspring overweight and obesity: a systematic review and meta-analysis. Int J Obes. 2013;37(7):893-9.

(10) Li HT, Ye R, Achenbach T, Ren A, Pei L, Zheng X*, Liu JM*. Caesarean delivery on maternal request and childhood psychopathology: a retrospective cohort study in China. BJOG. 2011;118(1):42-8.

Main research progress

Whether to have a child and how to give births are two fundamental issues in the field of women, children, and reproductive health. They are also hot topics of concern to the government, the public, and society. In recent years, our team has conducted a series of studies focusing on these two issues. Some typical works include:

(I) Study on Birth Population Monitoring and the Effects of Adjustments in Fertility Policies

The new round of family planning policy adjustments (including the implementation of the selective two-child policy in 2014 and the universal two-child policy in 2016) is a significant national strategy and also a focus of attention for academic peers and the public.

In 2015, the second year of the implementation of the selective two-child policy, there were predictions that the birth population would increase by about 2 million, but the actual birth population decreased instead of increasing, causing concerns about the effectiveness of the policy. The team comprehensively applied spatial epidemiology and time series research methods to systematically analyze the spatiotemporal distribution patterns of the birth population over the past 20 years, proposing that the encounter of the Year of the Sheep with the selective two-child policy was the main reason for the decrease in the birth population, rather than an increase. This conclusion overturned the previous mainstream view that there was no taboo against the zodiac sign of the Sheep, providing direct support for scientifically judging the effects of the selective two-child policy (Sci Bull 2018;63:1235-1237).

Since the implementation of the universal two-child policy in 2016, the increase in birth population and changes in critical characteristics of mothers and infants have been highly anticipated. Utilizing difference-in-differences and segmented regression models, our team analyzed live birth and delivery data from most provinces in China. We found that the policy effects began to emerge approximately nine months after implementation, resulting in an estimated cumulative increase of about 5.4 million births by the end of 2017. Compared to 2016, there was a significant decrease in the number of first-time births in 2017, explaining why the total birth rate failed to increase despite the effectiveness of the policy. Furthermore, we observed an increase in the proportion of multiparous women and older mothers after the policy took effect, peaking around February 2017 with increases of approximately 9 and 6 percentage points respectively. However, by the end of 2017, there were signs of a decline in both the increment of the birth population and the proportion of multiparous and older mothers. Based on these findings, we proposed a scientific conclusion that the concentrated release of cumulative fertility demand might have entered a decline phase after experiencing an upward and plateau period. This study, based on empirical analysis of big data, addresses the issue of population growth brought about by the universal two-child policy, providing important evidence for scientifically assessing the policy effects and the situation of maternal and infant safety (BMJ 2019;366:l4680).

(II) Research on the Spatial-temporal Distribution Characteristics of Cesarean Section Rate in China

The overuse of cesarean section is not only a medical issue but also a social one. A survey conducted by the World Health Organization in nine Asian countries revealed that China's cesarean section rate was 46% in 2007-2008, ranking first in Asia, earning China the title of having the highest cesarean section rate. The People's Daily even warned of China's excessively high cesarean section rate. However, it is worth noting that China has a large population base, vast territory, and uneven regional maternal and child health service capabilities, and the World Health Organization's survey may overestimate the rate owing to its sampling method. There is a lack of authoritative data on the average national cesarean section rate, differences between provinces, cities, and counties, and trends in cesarean section rates.

Utilizing national delivery data from 2008 to 2014, the team conducted in-depth research on the spatial-temporal distribution characteristics of cesarean section rates in China using spatial epidemiology and multi-level data analysis methods. It was found that the national average cesarean section rate was only about 29% in 2008 and 34.9% in 2014, significantly lower than the level reported by the World Health Organization. This data removes the "title" of having the highest cesarean section rate of China in the world. It was also found that the trends in cesarean section rates varied significantly among districts and counties with different characteristics. In economically underdeveloped areas with low cesarean section rates in 2008, the cesarean section rate showed a steady upward trend, affirming the effectiveness of policies such as strengthening maternal and child health service capabilities and improving the accessibility of inpatient delivery services in rural areas in recent years. In contrast, in economically relatively developed areas with high cesarean section rates in 2008, the cesarean section rate showed a downward trend, reflecting the effectiveness of a series of measures to reduce cesarean sections. The downward trend in cesarean section rates in megacities was particularly significant, and the decline did not lead to an increase in maternal and perinatal mortality rates, providing a basis for other countries and regions with high cesarean section rates to set reduction targets. It was also found that there were significant differences in cesarean section rates between different provinces and districts, with both severe underutilization and excessive use beyond medical needs coexisting. Based on this, it was proposed that differentiated policies need to be strengthened to reduce variations in cesarean section rates, optimize resource allocation, and improve maternal and child health (JAMA 2017;317:69-76). The research has been reported by Xinhua News Agency, Guangming Daily, People's Daily Online, and other media, and continues to rank among the highly cited papers on Web of Science.

The team subsequently continued to analyze the characteristics of changes in cesarean section rates in China and found that the national cesarean section rate generally showed a pattern of "rising first, then stabilizing, and rising again" from 2008 to 2018: the cesarean section rate increased annually by 4.6% before 2012, remained largely stable from 2012 to 2016, and then increased annually by 3.5% after 2016. Megacities, general cities, and rural areas showed different trends, with the gap in cesarean section rates between megacities and rural areas narrowing from 25.1% in 2008 to 9.6% in 2018, a reduction of more than 60% (JAMA 2020;323:89-91). These results provide evidence for grasping the current status of cesarean section in China in the new era, judging future trends, and have high reference value for adjusting and improving relevant policies.

(III) Providing Compelling Evidence for the Causal Relationship between Cesarean Delivery and Offspring Health

With the rapid increase in the cesarean delivery rate, its health effects have attracted widespread attention. There is already consensus on the impact of cesarean delivery on maternal health, while its effects on offspring health have become an academic hot topic. A series of studies have therefore been conducted focusing on the relationship between cesarean delivery and childhood overweight, obesity, anemia, and other conditions, including cohort studies, systematic reviews and meta-analyses, randomized controlled clinical trials, animal experiments, and statistical simulation studies, providing compelling evidence of the effects of cesarean delivery on offspring health.

In 2012, a study based on data from six follow-ups of three birth cohorts found that the risk of obesity in offspring delivered by cesarean section was 6%-31% higher than that of offspring delivered vaginally, but the differences were not statistically significant. Our team summarized the results of these six follow-ups and proposed that cesarean delivery would increase the risk of obesity in offspring (Am J Clin Nutr 2012;96:215-216). Subsequently, our team conducted a systematic review and meta-analysis, combining nine studies, and concluded that cesarean delivery would increase the risk of childhood overweight/obesity (Int J Obes 2013;37:893-899), which was selected as an editor's choice. Given that previous studies did not distinguish between medically indicated cesarean deliveries and cesarean deliveries requested by pregnant women without medical indications, our team further studied the association between pregnant women's requests for cesarean delivery and childhood overweight based on a large-scale cohort, finding that pregnant women's requests for cesarean delivery would also increase the risk of childhood overweight (Pediatr Obes 2014;9:10-16). This discovery has important public health and etiological value. In addition to overweight and obesity, the team also found that cesarean delivery increased the risk of childhood anemia (Am J Clin Nutr 2015;101:523-529).

There are mainly two types of methods for previous studies on the relationship between cesarean delivery and offspring health: cohort studies and sibling control studies. However, the conclusions of these two types of studies are obviously inconsistent, which has confused the academic community. Cohort studies have often found that cesarean delivery increases the risk of various diseases in offspring, while sibling control studies have often found no significant difference in the risk of diseases between offspring delivered by cesarean section and vaginal delivery. Which conclusion is more reliable? In the past, it was almost unanimously believed that sibling control studies were more reliable. Given that sibling control studies are more susceptible to interference from the confounding effect of delivery age compared to cohort studies, our team proposed a hypothesis: sibling control studies are not reliable in demonstrating the relationship between cesarean delivery and offspring health. To prove this hypothesis, the team conducted comparative meta-analysis and statistical simulation studies, confirming that the insignificant impact of cesarean delivery on offspring health in sibling control studies was a false impression caused by the confounding effect of delivery age. Relatively speaking, the results of cohort studies are more credible (BMC Med 2023;21:348). Given the limitations of cohort studies in demonstrating weak causal associations, our team further conducted animal experiments on rats, finding that compared to offspring delivered vaginally, offspring delivered by cesarean section exhibited faster weight gain and higher levels of multiple metabolic syndrome indicators such as triglycerides. Additionally, a high-sugar/high-fat diet exacerbated the difference in metabolic indicators between offspring delivered by cesarean section and vaginal delivery (Pediatr Res 2024. DOI: 10.1038/s41390-024-03079-6).

Future Work

We plan to continue conducting epidemiological research focused on birth population monitoring and fertility characteristics, providing a basis for the country to adjust and improve relevant policies. Additionally, we will further investigate the impact of negative exposures in early life, such as cesarean delivery, on the health of offspring, including prove into the causal relationship and exploring relevant mechanisms. We will also engage in research on the utilization of multi-source big data related to reproductive health issues, conduct transformational applied research on appropriate technologies for women, children, and reproductive health, and carry out research on the development and evaluation of products related to maternal and child health.

Key research areas include:

(1) Epidemiological research on birth population monitoring and fertility characteristics.

(2) Research on the causal relationship and underlying mechanism between negative exposures in early life, such as cesarean delivery, and the health of offspring, and to explore potential intervention strategies.

(3) Research on the development, evaluation, and transformational application of appropriate technologies related to women, children, and fertility health.