Objective To investigate the risk factors of fertility behaviors with preterm birth and low birth weight， and to develop a nomogram model to predict the occurrence of low birth weight.
Methods Birth registration information in Shanghai from 2010 to 2020 was collected， and ANOVA and Chi-square tests were used to compare the differences in reproductive behavior factors and newborn health status across time. The odds ratio （OR） value and 95%CI were calculated by a multi-classification logistic regression model to determine the association between reproductive behavior factors and preterm birth or low birth weight infants. A nomogram model was established based on logistic model and the area under the ROC curve was used to assess the effect of the model.
Results This analysis included 2 089 384 live newborns. The incidence of full-term low birth weight， preterm normal weight and preterm low birth weight in Shanghai was 0.94%， 2.48% and 2.01%， respectively. From 2010 to 2020， 40.00% women had a history of abortion， the proportion of women who gave birth at age ≥40 years old increased from 1.05% to 2.24%， the proportion of fathers aged ≥40 years increased from 4.79% to 7.48%， and the proportion of women with postgraduate or above increased from 4.81% to 11.74%. The incidence of preterm low birth weight in Shanghai showed an increasing trend over time. Logistic regression analysis showed that the risk of preterm low birth weight was lower in female than in male infants （OR=0.97， 95%CI： 0.95‒0.98）， and the risk of full-term low birth weight was higher than in male infants （OR=1.85， 95%CI： 1.80‒1.90）. The risk of preterm birth and low birth weight was lower for couples of childbearing age with higher education. The risk of preterm low birth weight in newborns tended to increase with maternal age at childbirth >30 years， paternal age ≥40 years， and the number of abortions >2 times. Mother <25 or >35 years， father aged 30‒34 years， and the number of abortions >3 times were the risk factors of full-term low birth weight infants.
Conclusion Couples of childbearing age who choose to have children at too high or too low age may increase the risk of preterm birth or low birth weight， so it is necessary to strengthen population awareness and promote age-appropriate childbirth. Multiple abortions are also associated with preterm birth and low birth weight， and it is advisable to popularize the scientific knowledge of contraception and birth control to reduce unnecessary abortions. The nomogram in the study can visualize the risk of full-term and low birth weight infant at different levels of factors， which can assist couples preparing for pregnancy in making decisions about the timing of childbirth and understanding the level of risk.
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