Factors Affecting the Risk of Postpartum Hemorrhage in Pregnant Women in Tibet Health Facilities.

BACKGROUND Postpartum hemorrhage (PPH), the leading cause of maternal death, is defined as a blood loss >500 mL within 24 h after vaginal delivery or >1000 mL within 24 h after cesarean section. This study aimed to investigate the incidence of PPH and assess its risk factors in pregnant women in Tibet to provide a reference for clinicians in this region. MATERIAL AND METHODS A total of 4796 pregnant women with gestational age ≥28 weeks who were admitted to hospitals in Tibet between December 2010 and December 2016 were involved in this study. Patient sociological and clinical data and pregnancy outcomes were collected. The related risk factors of PPH were analyzed by univariate and multivariable logistic regression. The area under the curve of the receiver operating characteristic curves was used to evaluate the effect of the PPH prediction model. RESULTS PPH occurred in 95 women, with an incidence of 1.98%. The following factors were associated with higher risk for PPH: maternal age ≥35 (odds ratio [OR]=1.96; 95% confidence interval [CI], 1.18-3.27; P=0.010), history of preterm birth (OR=2.66; 95% CI, 1.60-4.42; P<0.001), cesarean section (OR=6.69; 95% CI, 4.30-10.40; P<0.001), neonatal weight >4 kg (OR=3.92; 95% CI, 1.75-8.81; P<0.001) and occurrence of neonatal asphyxia (OR=5.52; 95% CI, 2.22-13.74; P<0.001). CONCLUSIONS Maternal age ≥35, history of preterm birth, cesarean section, newborn weight >4 kg, and neonatal asphyxia were risk factors of PPH, which can help evaluate PPH in Tibet.

Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA.

As modern humans migrated out of Africa, they encountered many new environmental conditions, including greater temperature extremes, different pathogens and higher altitudes. These diverse environments are likely to have acted as agents of natural selection and to have led to local adaptations. One of the most celebrated examples in humans is the adaptation of Tibetans to the hypoxic environment of the high-altitude Tibetan plateau. A hypoxia pathway gene, EPAS1, was previously identified as having the most extreme signature of positive selection in Tibetans, and was shown to be associated with differences in haemoglobin concentration at high altitude. Re-sequencing the region around EPAS1 in 40 Tibetan and 40 Han individuals, we find that this gene has a highly unusual haplotype structure that can only be convincingly explained by introgression of DNA from Denisovan or Denisovan-related individuals into humans. Scanning a larger set of worldwide populations, we find that the selected haplotype is only found in Denisovans and in Tibetans, and at very low frequency among Han Chinese. Furthermore, the length of the haplotype, and the fact that it is not found in any other populations, makes it unlikely that the haplotype sharing between Tibetans and Denisovans was caused by incomplete ancestral lineage sorting rather than introgression. Our findings illustrate that admixture with other hominin species has provided genetic variation that helped humans to adapt to new environments.

Prevalence and causes of cesarean births among women residing at high altitude in Lhasa, Tibet: A retrospective observational study of 7365 women.

OBJECTIVE: Currently, there is paucity of data on the rate of vaginal deliveries and cesarean section among women in Tibet. In this study, we carried out an observational study of 7365 consecutive pregnant women in Lhasa, Tibet who gave birth at our tertiary care institution between 2012 and 2015. MATERIALS AND METHODS: In this retrospective study, we reviewed the hospital records for demographic data, obstetric history, and the number of vaginal and emergency cesarean section deliveries. The overall and annual rate of vaginal and cesarean section deliveries was calculated. Causes, indications or risks for cesarean section were also analyzed. RESULTS: During the review period, 7365 neonates were delivered at our hospital, including 1690 (23.0%) deliveries via cesarean section. The yearly rate of cesarean section progressively declined from 26.7% in 2012 to 18% in 2015 (P < 0.001). Furthermore, the annual rate of emergency cesarean section declined 53.9%between 2012 and 2015(P < 0.001). Fetal risk factors (39.9%) and maternal risk factors (40.3%) were the major causes of cesarean section in the women. Social factors as a cause of cesarean section fluctuated between 7.9% and 11.1%. CONCLUSION: This study has demonstrated a steady decline in the annual rate of cesarean section in women in Tibet between 2012 and 2015. A decrease in the rate of emergency cesarean section contributed substantially to this decline. Moreover, approximately 10% caesarian sections were performed without clear indications, highlighting the need for strengthening prenatal counseling for pregnant women in Tibet.

Sequencing of 50 human exomes reveals adaptation to high altitude.

Residents of the Tibetan Plateau show heritable adaptations to extreme altitude. We sequenced 50 exomes of ethnic Tibetans, encompassing coding sequences of 92% of human genes, with an average coverage of 18x per individual. Genes showing population-specific allele frequency changes, which represent strong candidates for altitude adaptation, were identified. The strongest signal of natural selection came from endothelial Per-Arnt-Sim (PAS) domain protein 1 (EPAS1), a transcription factor involved in response to hypoxia. One single-nucleotide polymorphism (SNP) at EPAS1 shows a 78% frequency difference between Tibetan and Han samples, representing the fastest allele frequency change observed at any human gene to date. This SNP's association with erythrocyte abundance supports the role of EPAS1 in adaptation to hypoxia. Thus, a population genomic survey has revealed a functionally important locus in genetic adaptation to high altitude.