Mannose-binding lectin (MBL) is a component of the innate immune system and acts as a complement activator through the lectin pathway. Genetic variations of MBL and low MBL levels cause several infection problems, which may also be related to pregnancy problems. We aimed to investigate the role of MBL gene codon 54 polymorphism and serum MBL levels in pregnancy problems and premature delivery. In this prospective study, MBL gene codon 54 polymorphism and serum MBL levels were studied in 45 mothers who delivered earlier than 35 gestational weeks. The frequency of MBL gene codon 54 variant allele B was much higher (homozygous 4.4% and heterozygous 33.3%) in the study group mothers than the previously reported frequency in the healthy Turkish population (homozygous 2-6%, heterozygous 12-20%). MBL variant allele B frequency was closely related to low MBL levels (<0.1 μg/ml), vaginitis and increased IL-6 levels. The median MBL levels were lower than the critical level of 0.1 μg/ ml in study mothers who had recurrent miscarriage, infertility, preeclampsia, gestational diabetes mellitus, preterm premature rupture of membranes with duration of longer than 72 hours, tocolysis, histological chorioamnionitis, urinary tract infection and vaginitis. MBL gene codon 54 variant allele B is related to low serum MBL levels, increased IL-6 levels, genitourinary infections and may cause pregnancy-related problems such as infertility, recurrent miscarriage and preterm delivery.