Conclusion
In conclusion, higher levels of serum ApoB and ApoB/ApoA-1 ratio during mid-pregnancy were associated with an increased risk of PTB among Chinese pregnant women. Monitoring and managing apolipoprotein levels during pregnancy may help to identify the high-risk population and reduce the risk of preterm birth. Further studies are needed to confirm the positive relationships between ApoB, ApoB/ApoA-1 during pregnancy and PTB and to explore the underlying mechanisms.