Antenatal factors associated with birth weight of twins and risk factors for discordant twins

Abstract

Objective To investigate the antenatal influencing factors associated with birth weight of twins and the risk factors for the occurrence of discordant twins. Methods Totally, 834 twins delivered at the Third Affiliated Hospital from January 2000 to December 2009 and the First Affiliated Hospital of SUN Yat sen University, from January 2000 to June 2009, were recruited in the study. The diagnosis criteria of discordant twins was intrapair birth weight difference more than 25%. Antenatal factors on birth weight were retrospectively investigated among twins and discordant twins respectively with Logistic analysis. Results （1） There were several factors associated with birth weight of twins, including maternal age, conceptive style, chorionicity, gestational diabetes mellitus and placental cord insertion （P = 0. 021, 0. 000, 0. 000, 0. 012 and 0. 017, respectively）. While hypertensive disorder in pregnancy, parity and fetal gender differences were not associated with the birth weight of twins （P〉0.05）. Hypertensive disorder in pregnancy （OR =2.600, 95% CI：1. 566 4. 316） and monochorionicity （OR=1.833, 95% CI：1.010-3.582） were risk factors of discordant twins. All 834 twin pregnancies were divided into 4 groups according to rnateral age, 〈25 yrs （n =69）, 25-30 yrs （n= 312）, 30-35 yrs （n=325） and ≥35 yrs （n=128）. The average birth weight of twins were （2205±483） g, （2347±406） g, （2381±439） g and （2352±455） g. Significant difference was found bewteen every two groups （P〈0.05） except that between the 30-35 yrs and ≥35 yrs group （P〉0.05）. Among twins of different gender （n=270）, the average birth weight of boys and girls were （2416±514） g and （2322±488） g, and that of female twins （n=272） and male twins （n 292） were （2301±418） g and （2381±428） g. Significant difference was shown between every two groups （P〈0.05） except that between the male twins and male fetus of twins of different gender （P〉0.05）. Conclusions The fetal birth weight of twins decreases remarkably when maternal age 〈 25, or monochorionicity twins, or complicated with marginal or velamentous placental cord insertion or female pairs. However, birth weight of twins would increase if the pregnancy conceived by assisted reproductive technology or complicated with gestational diabetes mellitus. Twin pregnancy complicated with hypertensive disorder in pregnancy or monoehorionicity should alert the clinicians of discordance twins. Key words: Twins; Birth weight; Risk factor