Association between the maternal protein nutrition status during pregnancy and the risk of preterm birth.

We aimed to assess protein nutrition status during pregnancy by maternal plasma total protein (MTP) levels in urban pregnant women and to explore the association between the trimester-specific MTP levels and risk of preterm birth (PTB). A prospective design was conducted in 3,382 mother-newborn pairs with the second-trimester maternal MTP information and in 3,478 mother-newborn pairs with the third-trimester MTP information. Multiple Cox proportional hazard regression and multiple linear regression were used to analyse the associations between MTP levels and PTB risk as well as gestational duration, respectively. Nearly all the second-trimester MTP levels were within the clinical reference range, but more than 40% of the third-trimester MTP levels were less than the lower limit of normal. No significant association was found between the second-trimester MTP level and PTB risk. However, the adjusted hazard ratios (HRs) of PTB across increasing quartiles of the third-trimester MTP levels were 1.00 (reference), 0.59 (0.36, 0.95), 0.35 (0.20, 0.60), and 0.32 (0.19, 0.53) (p for trend < 0.001), respectively. Each standard deviations increment of the third-trimester MTP was associated with increase of 0.13 weeks in gestational duration. Moreover, stratified analyses showed that the effects of third-trimester MTP on PTB risk and gestational duration were stronger in pregnant women carrying female offspring than those carrying male offspring (p for interaction < 0.05). The third-trimester MTP level was inversely associated with PTB risk and was positively associated with gestational duration. Improving third-trimester MTP level may be helpful for preventing PTB.