Materials and Methods: In this cohort study, the statistical population was pregnant women. After collecting all the primary information, the relationship between pre-pregnancy body mass index (BMI) and weight gain during pregnancy with preterm delivery and maternal complications such as diabetes and pre-eclampsia were studied.

Results: From a total of 1400 pregnant women, who were recruited for this study, 897 were referred to Bushehr’s Persian Gulf Martyrs Hospital; statistical analysis was performed on the participants. BMI before pregnancy had no significant relationship with the number of previous abortions (P = 0.3). No significant relationship was found between BMI before pregnancy and gestational diabetes during pregnancy (P = 0.53), preeclampsia (P = 0.26), or preterm delivery (P = 0.55). Weekly weight gain was significantly less in mothers without preterm birth than mothers with preterm birth (P = 0.002), but there was no significant difference in overall weight (P = 0.99). BMI had a significant impact on low birth weight (LBW) in infants (P = 0.003). The impact of pre-pregnancy BMI on Apgar scores was significant (P = 0.043). The mother’s BMI and weekly weight gain (without adjusting for confounding variables) as well as weight gain after adjusting for confounding variables had no significant effect on the mother’s risk of developing gestational diabetes. The mother’s age was the only confused variable (adjusted odds ratio [OR] = 1.09, P = 0.004). Pre-pregnancy BMI had a significant impact on the chances of Small for gestational age (SGA) infants (P = 0.03), but no significant effect on the chance of large for gestational age (LGA) births (P >0.05).

Conclusion: High BMI during pregnancy has an adverse outcome in pregnancy.