Materials and Methods

Our study group included pregnant patients who were referred to a specialized fetal medicine clinic at the Sheba Medical Center in Israel for counseling and prenatal diagnostic workup for primary maternal CMV infection from January 2000 to December 2006.

Although there is no formal CMV screening program in Israel, it is a common practice of most obstetricians to advise patients to undergo CMV screening before planned pregnancy or during the first trimester of an ongoing pregnancy. CMV serological screening was performed with different commercially available kits for specific anti-CMV immunoglobulin G (IgG) and immunoglobulin M (IgM) as well as an IgG avidity test in IgG-positive patients. IgG seronegative women were reassessed during pregnancy. Patients considered screen positive by their primary care obstetricians were referred for further prenatal investigation and follow-up. Twelve patients had also minor, mostly unrelated, ultrasound findings or unspecific maternal symptoms described in the referral letter. However, each study subject had CMV infection documented by serologic assays.

All referred patients were primarily interviewed and counseled by fetal medicine specialist. Medical and obstetrical history as well as the detailed course of the ongoing pregnancy was documented. Precise gestational dating was determined by the first day of the last menstrual period (LMP) and ultrasonography at the first trimester.

Diagnosis of primary maternal CMV infection was exclusively determined by IgG seroconversion (the appearance of de novo-specific IgG antibodies in a previously seronegative patient) or positive specific anti-CMV IgG and IgM antibodies associated with low IgG avidity.

Timing of maternal infection was very carefully related to gestational age. Each patient was assigned to 1 of the 5 following subgroups: pregestational (12 months to 8 weeks before conception), periconception (between 8 weeks before and 6 weeks after conception), first trimester (up to full 13 weeks), second trimester (up to full 26 weeks), and third trimester (gestational age beyond 26 weeks).

Clear-cut differentiation between gestational and pregestational maternal infection is desired, however impossible in many around-conception cases. Therefore, we chose to define a group of periconception. Patients were assigned to first-trimester maternal infection when the serological data clearly supported it (IgG seroconversion during the first trimester or positive IgG and IgM associated with low IgG avidity beyond 8 weeks after conception). Patients were assigned to the periconception group when the serology was highly indicative of infection during the time period of 8 weeks before and 6 weeks after conception (IgG seroconversion) or when the data were not clearly indicative of first-trimester infection (low IgG avidity before 8 weeks after conception).

Following the initial evaluation and counseling, all patients were offered to participate in our prenatal CMV diagnosis program, which includes amniocentesis and repeated detailed ultrasonographic evaluation. Amniocentesis was performed after 21 weeks from the LMP, allowing an interval of at least 7 weeks between the estimated date of maternal infection and the date of the invasive procedure. Transabdominal ultrasound-guided amniocentesis was performed using a 21-gauge needle to collect 30 mL of amniotic fluid for CMV assays and fetal karyotyping. Infectious virus was detected in amniotic fluid samples by rapid virus isolation in cell cultures (shell vial procedure), whereas the presence of viral genome was determined by polymerase chain reaction.

Patients with proven fetal infection had a postamniocentesis counseling session. The risks of fetal CMV infection were discussed, and patients were offered to participate in a pre- and postnatal follow-up program. Serial detailed ultrasound examinations were performed every 3-4 weeks until delivery. Magnetic resonance imaging examination directed to identify fetal central nervous system pathology associated with CMV infection was also performed in these cases since August 2004.

Neonatal urine was tested after birth for CMV during the first 7 days of life to determine whether congenital CMV infection is present. All neonates with positive urine culture or prenatally documented CMV infection had a fundus examination, hearing evaluation, and brain ultrasound scan during the first few days of life. Results of these tests were obtained from hospital charts. The parents were referred for long term follow-up including a physical examination and hearing test in a pediatric infectious diseases unit at a near-home tertiary medical center. Information on the long-term follow-up was obtained from telephone interviews of the parents.

Data were prospectively collected and retrospectively evaluated for each case. Transmission rates were compared using the χ ² test. The study was approved by the institutional review board.