PRENATAL DIAGNOSIS Prenat Diagn 2011; 31: 995–998. Published online 11 July 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/pd.2823 Second trimester biparietal diameter size and the risk of adverse pregnancy outcomes Vajiheh Marsoosi 1 , Reihaneh Pirjani 1 *, Ashraf Jamal 1 , Laleh Eslamian 1 and Abbas Rahimi-Foroushani 2 1 Perinatology Division, Obstetrics and Gynecology Department, Tehran University of Medical Sciences, Tehran, Iran 2 Epidemiology and biostatistics Department, School of Public Health Sciences, Tehran Universtiy of Medical Sciences, Tehran, Iran Objective To identify the relationship between biparietal diameter (BPD) in the second trimester and adverse pregnancy outcomes in low-risk pregnancies. Method This prospective cohort study was performed on 2219 singleton pregnant women from August 2008 to March 2010. The gestational age-specific percentiles of BPD at 17 to 24 weeks of gestation were established to categorize participants into three groups: a BPD <10th percentile as small BPD, between 10th and 90th percentile as normal BPD and >90th percentile as large BPD. Using logistic regression analysis, the association between BPD <10th and >90th percentile with pregnancy outcomes was evaluated after controlling for confounding factors. Results There was a significantly increased risk of macrosomia [odds ratio (OR adj ) = 2.1; 95% confidence intervals (CI), 1.23–3.78] and preterm labor (PTL) (OR adj = 1.9; 95% CI, 1.19–3.05) in fetuses with a BPD >90th percentile compared with fetuses with a normal BPD, and there was a significant relationship between small for gestational age (SGA) at delivery and a BPD <10th percentile at the second trimester (OR adj = 2.4; 95% CI, 1.77–3.52). No association was present between preeclampsia and second trimester BPD. Conclusion BPD in the first half of pregnancy is related to fetal size at term and risk of PTL. Copyright  2011 John Wiley & Sons, Ltd. KEY WORDS: BPD; second trimester; preterm labor; SGA; pregnancy outcomes; macrosomia INTRODUCTION Fetal growth is a noticeable indicator of fetal health. Experience and research have shown that fetal growth restriction is associated with increased risk for perinatal morbidity and mortality in the current pregnancy (Smith et al., 1998; Pedersen et al., 2008b; Salomon, 2010) and even in subsequent pregnancies (Garite et al., 2004; Kady and Gardosi, 2004; Smith, 2004; Rasmussen et al., 2006; Law et al., 2009), as well as a long-term effect on risk of obesity and morbidity in adult life. Fetal macrosomia can be associated with increased perinatal risks, including shoulder dystocia, asphyxia, soft tissue trauma and perinatal death. Hackmon et al. (2008) described that severe macrosomia can be predicted as early as 11 to 14 weeks of gestation. Preterm labor (PTL) is another adverse pregnancy outcome with multifactorial etiologies, which can be associated with disordered fetal growth [either growth restriction or large for gestational age (GA)]. Early prediction of these complications would be desirable as it may help to decrease associated morbidity and mortality. Recent studies have shown that fetal growth is not uniform even in early pregnancy (Smith et al., 1998; *Correspondence to: Reihaneh Pirjani, Perinatology Division, Obstetrics and Gynecology Department, Tehran University of Medical Sciences, Tehran, Iran. E-mail: pirjani@razi.tums.ac.ir Hackmon et al., 2008; Pedersen et al., 2008b; Lampl et al., 2009). Furthermore, late pregnancy complications may arise from conditions occurring earlier in gestation. It is plausible that the same factors that affect early fetal growth may also affect pregnancy outcomes. The aim of this study was to determine whether biparietal diameter (BPD) <10th and >90th percentile in early second trimester in low-risk pregnancies is associated with adverse pregnancy outcomes, including preeclampsia, PTL, small for gestational age (SGA) and macrosomia. METHODS This prospective cohort study was conducted from August 2008 to March 2010 at three University Hos- pitals. In our department, at least two ultrasound exami- nations are routinely performed on all pregnant women, one between 11 and 14 gestational weeks and another between 18 and 24 gestational weeks. The inclusion cri- teria for this study were singleton pregnancy with viable fetus, first prenanal visit prior to 14 weeks of gesta- tion, both first and second sonographic examinations at one of our hospitals, and delivery at the same hospital. Exclusion criteria were multiple gestation, major fetal malformations, fetal aneuploidy, history of Rh immu- nization, spontaneous or therapeutic pregnancy termina- tion before 20 weeks of gestation, smoking, maternal Copyright  2011 John Wiley & Sons, Ltd. Received: 17 March 2011 Revised: 9 June 2011 Accepted: 9 June 2011 Published online: 11 July 2011