Vaccination during pregnancy

Measles-mumps-rubella vaccine

Wild-type rubella infection might result in spontaneous abortion, stillbirth, and, of most concern, congenital rubella syndrome (CRS), with its hallmark characteristics of sensorineural deafness, congenital heart defects, microcephaly, learning difficulties, and eye and bone defects. Measles infection in pregnancy might result in substantial maternal morbidity, an increased abortion rate, prematurity, stillbirth, and possibly congenital malformations. The data for mumps infection are not consistent, with some studies showing a possible increased rate of spontaneous abortion.²

There have been no reports of congenital malformations attributable to the MMR vaccine virus. The Centers for Disease Control and Prevention (CDC) estimated the theoretical risk to the fetus of CRS following vaccination with the rubella vaccine to be 0% to 1.6%.² In 1971, the CDC established the Vaccine in Pregnancy registry of women who had received rubella vaccines within 3 months before or after conception. By 1989 there were data on 1221 inadvertently vaccinated pregnant women. There was no evidence of an increase in fetal abnormalities or cases of CRS in the enrolled women or the 321 rubella-susceptible women; therefore, enrolment in the registry ended.^2,3

Motherisk conducted a prospective controlled study that included 94 women exposed to the rubella vaccine in the 3 months before conception or during the first trimester of pregnancy. The Motherisk team reported no difference in pregnancy outcomes or malformation rates between the exposed and the nonexposed groups, and no adverse effects consistent with CRS.⁴ These data have been confirmed in other immunization campaigns and studies.^5–8

Varicella vaccine

Varicella virus infection during pregnancy is associated with a risk of congenital varicella syndrome, characterized by low birth weight, skin scarring, ophthalmologic defects, limb hypoplasia of bone and muscle, neuropathic bladder, and gastrointestinal and neurologic abnormalities.⁹

There are no reports of congenital varicella syndrome after exposure to varicella vaccine during pregnancy. A registry was established by the manufacturer in collaboration with the CDC to monitor maternal and fetal outcomes of women who were inadvertently immunized with varicella vaccine in the 3 months before conception or at any time during pregnancy. Among the 737 women with pregnancy outcomes available, there were no patterns of defects and no infants were born with features consistent with congenital varicella syndrome among any of the women enrolled or among the seronegative women.¹⁰

Hepatitis B (HB) vaccine

Hepatitis B infection in a pregnant woman might result in severe disease for the mother and possibly an increase in preterm birth; however, it is not associated with increased abortion rates, stillbirth, or congenital malformation. Therefore, the biggest concern of maternal infection is vertical transmission of the virus to the offspring, as 70% to 90% of babies will remain chronically infected into adult life and be prone to cirrhosis and hepatocellular carcinoma.¹¹ The HB vaccine is an inactivated (recombinant) virus vaccine; and because the vaccine is composed of noninfectious HB surface antigen particles, it should theoretically cause no increased risk.¹² There were no adverse pregnancy outcomes reported in several small studies following women vaccinated with HB vaccine during pregnancy.^13–16

Although there is limited evidence, there appears to be no increased risk of adverse fetal outcomes when the HB vaccine is administered during pregnancy. Pregnancy is therefore not considered a contraindication to vaccination, and the Advisory Committee on Immunization Practices (ACIP)¹² and the Public Health Agency of Canada¹⁷ recommend that the vaccine should be offered to pregnant women at high risk of acquiring HB infection.

Tetanus

Tetanus can cause severe morbidity in the mother and mortality in the neonate.¹⁸ The tetanus vaccine contains noninfectious toxoids. The American Congress of Obstetricians and Gynecologists recommends use of tetanus immune globulin, as there is no evidence of any adverse effects to the fetus from the vaccine.¹⁹ In addition, Dastur and colleagues evaluated the efficacy and safety of a single-dose tetanus toxoid on 200 unimmunized primigravidae women in the last trimester of pregnancy. No adverse effects were encountered in the mothers and there was no increase in stillbirths.²⁰ These results were confirmed in 2 case-control studies.^18,21

The ACIP recommends that pregnant women receive the combined tetanus and diphtheria vaccine if indicated. Previously vaccinated pregnant women who lack the primary series of immunizations or who have not received booster shots in the past 10 years should complete the primary series or receive booster doses. Even though there is no evidence that tetanus and diphtheria toxoids are teratogenic, vaccination during the second or third trimester is preferred.²² Also, immunization will protect the mother for several years and passively protect the infant for several months after delivery.²³