Abstract: Objective To examine the effect of first trimester vomiting on adverse pregnancy outcomes including small for gestational age (SGA),premature birth (PB),and low birth weight (LBW).Methods Subjects were 5 084 pregnant women who had joined in the Ma'anshan Birth Cohort Study and delivered between October 2008 and October 2010.The relationships between different vomiting and adverse pregnancy outcomes were evaluated by chi-square analysis and non-conditional logistic regression.Results Of the 4 653 women with singleton alive pregnancy,2 937 had nausea and vomiting,175 had hyperemesis gravidarum(HG),and 1 541 did not experience vomiting.After adjusting for several risk factors,mothers with nausea and vomiting in pregnancy (NVP) in the first trimester had a 0.66 time (relative risk=0.66,95% confidence interval:0.45-0.96)of giving birth to small for gestational age infants compared to the women with no vomiting in pregnany.The mothers with HG had a 2.76 times (RR=2.76,95%CI:1.51-5.05) of giving birth to small for gestational age infants compared to the women with no vomiting in pregnancy.Conclusion No vomiting or HG during the first trimester of pregnancy have different effects on small for gestational age.