Introduction: The association between obesity before pregnancy and preterm birth varies with age and ethnicity. Objective: To study the association between early body mass index (BMI) and risk of preterm birth in Chinese women. Methods: This was a hospital-based retrospective cohort study including 36,596 Chinese women who gave birth to a live singleton infant from 2015 to 2018. Women were classified as underweight (BMI < 18.5), normal weight (BMI 18.5 to < 23), overweight (BMI 23 to < 27.5), or obese (BMI ≥27.5) according to the most recent criteria for Asian women. Multivariate log-binomial regression models were used to estimate the relative risks (RRs) and 95% confidence intervals (95% CIs) for preterm birth among different groups. Results: Compared to women with normal weight, women with overweight or obesity before pregnancy had an increased risk of preterm birth; the RRs and 95% CIs were 1.22 (95% CI: 1.08-1.37) and 1.30 (95% CI: 1.01-1.69), respectively. The greatest risk of extremely preterm birth was observed in obese women. The estimators were robust when considering the maternal age and rate of gestational weight gain (GWG) during pregnancy. Conclusions: Women with overweight and obesity had an increased risk of preterm birth regardless of GWG in early pregnancy. Our study suggests that it is beneficial to lose weight before conception for both overweight and obese women who plan to become pregnant.
Background Thyroid hormones are associated with birth weight in singleton pregnancy. Twin pregnancies need more thyroid hormones to maintain the normal growth and development of the fetuses compared with single pregnancy. We aimed to investigate the association of thyroid hormones and birth weight in twins. Method This was a retrospective cohort study in Chinese population. Pregnant women who received regular antenatal health care and delivered live-born twins from 2014 to 2019 were included (n=1626). Linear mixed model with restricted cubic splines and logistic regression models were used to estimate the association of thyroid hormones with birth weight and birth weight discordance in twins. Results We observed that both thyroid-stimulating hormone (TSH) and free thyroxine (FT4) were not associated with birth weight in twins overall. While when stratifying on fetal sex or chorionicity, there were non-linear association between FT4 levels and birth weight in boys (Pnon-linear<0.001) and in dichorionic (DC) twins (Pnon-linear=0.0295). Women with levels of FT4 lower than the 10 th percentile had a higher risk of birth weight discordance in their offsprings than women with normal FT4 levels (range from the 2.5 to 97.5 percentiles) (odds ratio=1.58, 95% confidence interval: 1.05, 2.33). Conclusion Our study suggested that there was an association of FT4, but not TSH, with birth weight and birth weight discordance varied by sex and chorionicity. These findings could have implications for obstetrician to be aware of importance of FT4 levels in prevention of birth weight discordance in twin pregnancy.
Phoebe hui is a precious timber tree species. In order to get excellent seedlings and stands with good genes and develop Phoebe hui better, it is necessary to select superior trees. The dominant trees comparative method and small sample plot method were used to evaluate and select Phoebe hui superior trees in Longshan county, Hunan province, and the evaluation factors included diameter at breast height (DBH), tree height, timber volume and other quality factors. The results showed that, using the dominant trees comparative method, the DBH, tree height and timber volume values of the superior tree were more than 1.12, 1.06 and 1.23 times of the mean values of 5 dominant trees respectively, and 6 superior trees were selected in two stands. Using small sample plot method, the DBH, tree height and timber volume of the superior tree were more than the mean value and 1 times standard deviation value of the stand, and 4 trees were selected as superior tree. These 2 methods can be used for superior tree selection of Phoebe hui in Hunan, and the dominant trees comparative method is more simple and easier for operation.
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