Exposure to IFN-beta Among Pregnant Patients With MS Poses No Risk to Infant Size, Study Says

The use of interferon-beta (IFN-beta) by pregnant patients with multiple sclerosis (MS) poses no risk to an infant’s birth weight, length, or head circumference, according to a recent study.

IFN-beta is a commonly used treatment among patients with MS. However, because pregnant women are not usually included in clinical trials, thus limiting research into the effects of prenatal exposure, IFN-beta’s guidelines currently advise women with MS to cease treatment during pregnancy.

Previous studies have yielded mixed results when it comes to IFN-beta exposure in pregnant women with MS. The authors of the current study argue their results “refute the findings of other studies which have found IFN-beta is associated with birth measurement.”

In this large-scale population-based study, the researchers compiled data from Swedish and Finnish Medical Birth Registers between 2005 and 2014. They then compared birth measurement data of infants of women with MS who were exposed to IFN-beta during pregnancy to infants of women with MS not exposed to MS disease modifying drugs (DMDs). Every pregnancy of a woman with MS in Sweden and Finland during the 9-year period was included in this study.

The exposure window for the study was from 6 months prior to a woman’s last menstrual period to the birth of the child. Exposure to the treatment was considered based on the individuals’ collection of a prescription of IFN-beta during the study window.

Swedish records show 411 pregnancies were identified as exposed to IFN-beta and 835 pregnancies were unexposed to MS DMDs. In Finland, 232 pregnancies were recorded as exposed to IFN-beta and 331 were absent of any MS DMDs.

Additionally, “in Sweden, there were 101 pregnancies comprised of 50 sibling sets identified as being differently exposed to IFN-beta. The corresponding numbers for Finland were 83 pregnancies comprised of 41 sibling sets.”

The study found the following results:

1. Relative to those unexposed, Swedish infants prenatally exposed to IFN-beta were, on average:

• 28 g (0.99 oz) heavier (P =.17)
• 0.01 cm (0.004 in) longer (P =.95)
• 0.14 cm (0.06 in) larger in head circumference (P =.13)

2. Finnish infants prenatally exposed to IFN-beta were, on average:

• 50 g (1.76 oz) lighter (P =.27)
• 0.02 cm (0.008 in) shorter (P =.92)
• 0.22 cm (0.09 in) smaller in head circumference (P =.15)

When comparing sibling size in both cohorts, researchers found “differences between siblings exposed and siblings unexposed to IFN-beta during pregnancy were minimal, and not statistically significant. The same was true when considering exposure to any MS DMD, relative to non-exposure to MS DMD.”

Significantly lower than average birth measurements have been reportedly associated with adverse health outcomes, including behavioral difficulties and health conditions such as coronary heart disease and diabetes.

Researchers speculate a possible reason IFN-betas may not influence birth measurements is due to the treatment’s pharmacokinetic characteristics.

“The placental barrier is a semipermeable tissue which separates fetal and maternal blood and is only permeable for substances with a low molecular weight,” the authors explain. Because IFN-beta is a polypeptide with a molecular weight too large to permeate the placental barrier, “The likelihood of IFN-beta therefore being able to directly affect the development of the fetus through permeation of fetal blood is unlikely and suggests the lack of an effect of IFN-beta on fetal growth measurements is biologically plausible,” they said.

Reference

Burkill S, Vattulainen P, Geissbuehler Y, et al. The association between exposure to interferon-beta during pregnancy and birth measurement in offspring of women with multiple sclerosis. PLoS One. 2019;14(12):e0227120. doi: 10.1371/journal.pone.0227120.