Original sample size considerations were based on estimating and comparing the rates of TT-CMV infection in VLBW infants born to CMV-seropositive mothers or CMV-seronegative mothers. Assuming a 2.55% TT-CMV rate for infants born to CMV-seropositive mothers and a 0.5% TT-CMV rate for infants born to CMV-seronegative mothers, a sample size of 650 infants per group would need to be recruited to detect a difference of approximately 2% in the TT-CMV rate with 80% power (2-sided Fisher's exact test at the 5% significance level).