The overall prevalence of anti-CMV IgG antibodies in our pregnant women was 68.3% (95% CI: 66.6–70.0), without any significant differences between age classes.
As first pregnancies in Italy generally occur later than they did in the past, the majority of women have already recovered from primary infection by the time they reach childbearing age and almost certainly by the time of their first pregnancy. Moreover, in this study 95% of the women had an age between 21 and 40 years while age classes of 20 or less than 20 and over 40 years were under-represented; so this could be a further cause of the lack of difference in seroprevalence.
On the basis of the results of the IgG avidity test, the cumulative incidence of CMV infection was 1.4% (95% CI: 0.97–1.83%), the density incidence was 0.8% (95% CI: 0.47–1.13), and the risk of infection was 0.5% (95% CI: 0.24–0.76%) without any significant differences by age.
Seroconversion or clinical data indicating acute infection were available for three of the five cases with moderate avidity in this study, thus moderate avidity was considered as a potential marker of acute infection. Moderate and low IgG avidity were considered together, and both were included in the calculation of incidence. However, the incidence may be an underestimate because only about half of the seronegative women underwent further screening in the second trimester and about one-third in the third, and so some cases of seroconversion may have been missed.
For the same reason, the proportion of primary infections (84.6%) occurring in the first trimester may be overestimated; however, assuming the same rate of seroconversion among the seronegative women who did not undergo further screening, the majority of primary infections occurred in the first trimester.
The fact that 84.6% of the primary infections occurred in the first trimester may have been due to different behaviors before the pregnancy was recognized, whereas greater care during pregnancy may lead to less exposure. The fact that there were no differences related to the age of the women indicates the same type of behavior at different ages. It is therefore important to start screening in the first trimester of pregnancy, when there is a greater risk of infection and in order to have initial findings to compare with subsequent follow-up. In the absence of baseline data, the presence of IgG without IgM in women undergoing their first screening in the third trimester raises doubts as it may be the result of a previous infection occurring at any time in life before the pregnancy; however, although this is statistically the most probable situation, the possibility of an infection occurring in the first trimester with the subsequent loss of IgM cannot be excluded.
Finally some limitations of the study must be taken into account as no outcome data for newborns, substantial loss to follow-up, and limited testing of IgG positive women for reinfections or reactivations. However, for the latter two cases, as there are no official recommendations, the follow-up was performed at the discretion of the general practitioner with compliance of pregnant woman who, above all, must pay for CMV antibody screening.
In conclusion, although screening is not recommended by any public health system (including Italy's) because of its cost/benefit ratio, it is actually adopted by many general practitioners in our area. Such screening provides an opportunity to identify seronegative women who can be counselled about using appropriate hygienic measures to prevent infection, especially in relation to their behavior with children, who are a major source of infection. Furthermore, the screening identified primary infections in pregnant women who could be referred to Reference Centers to check for prenatal infection. Amniocentesis, funicolocentesis, ultrasonography, and magnetic resonance imaging can all be used to detect infection and allow the planning of appropriate interventions (e.g., antiviral therapy, termination of pregnancy).
Although some authors consider that screening is not justified on the grounds of its economic cost, the imperfect nature of congenital infection prognostic criteria, the risk of spontaneous abortions induced by invasive tests such as amniocentesis, and the few data concerning effective treatments during pregnancy, it is unthinkable to deny pregnant women appropriate information concerning the health of their unborn child as this raises a number of ethical and legal questions.
The incidence and risk of CMV infection in pregnancy found in our area, therefore, support the use of serological screening, certainly in the first trimester when the risk of infection is higher and, in the case of seronegative women, possibly also one screening in the second trimester and one in the third.