Study Estimates Risks of MG-related Problems During Pregnancy at 34%
The risk of myasthenia gravis (MG) worsening during pregnancy is about 34%, a new study estimates.
Notably, most MG pregnancies end in vaginal delivery, and the risk of preterm birth is not increased in women with the neuromuscular condition, the study also indicates.
“The current study allows the current best risk estimates for use in counselling regarding disease behaviour as well as the risk of myasthenic and pregnancy complications,” the researchers wrote.
The study, “Myasthenia Gravis in pregnancy: Systematic review and case series,” was published in the journal Obstetric Medicine.
MG is an autoimmune disease in which the body’s immune system erroneously launches an attack that interferes with communication between nerves and muscles, resulting in muscle weakness and other symptoms.
People with MG may experience times when symptoms suddenly worsen, called exacerbations. A more severe, potentially life-threatening condition called MG crisis also can occur, in which the disease causes weakness in muscles that are required for breathing.
During pregnancy, the body goes through a number of changes — for example, altered hormone levels — that could plausibly influence the course of autoimmune diseases like MG. However, it is not exactly clear how MG tends to manifest during pregnancy, or whether the disease is associated with a higher risk of problems for babies born to women with MG.
To learn more, researchers from the University of Toronto, in Canada, analyzed data from 32 previously published studies, as well as data from 48 pregnancies in 39 MG patients at their institution. In total, the analysis included data from 22 different countries collected from 1947 through 2020.
The goal was to better understand the association between pregnancy and MG-related risks.
“The current systematic review represents an accumulation of data, which to our knowledge has not previously been synthesized systematically,” the team wrote.
Across all studies with available data, the rate of MG exacerbations during pregnancy was 181 out of 535 (33.8%). MG symptoms remained stable during pregnancy in 242 of 505 patients (47.9%) with available data, while for 100 of 505 patients (19.8%), MG symptoms eased during pregnancy.
The rate of MG crisis during pregnancy was 23 of 357 (6.4%), while the rate of MG crisis in the postpartum period, or immediately after birth, was 31 of 380 (8.2%).
The majority of pregnancies — 464 of 824 (56.3%) — ended in a spontaneous vaginal birth. About a third of the babies were delivered by cesarean section, but this was usually for reasons other than MG.
The risk of preterm pre-labor rupture of membranes (PPROM), a pregnancy complication that can increase the risk of fetal infection as membranes surrounding the fetus rupture prematurely, was about 6.7% in MG pregnancies. This proportion is notably higher than that seen in the general population, where this complication occurs in about 3% of pregnancies.
However, rates for preterm births in MG pregnancies were not significantly different from those seen in the general population. Additionally, 14.1% of babies born from MG pregnancies were under the 10th percentile of birthweight for their gestational age.
“MG does not appear to significantly increase the rate of other pregnancy complications, with the exception of PPROM, which occurs at a rate roughly double that of the general population,” the researchers wrote.
Transient neonatal myasthenia gravis (TNMG) — a rare condition in which MG-causing antibodies cross over the placenta to the fetus during pregnancy, causing temporary MG-like symptoms in newborns — occurred in 13% of MG pregnancies.
According to the researchers, the risk factors for TNMG remain unclear. But the team said expectant parents with MG and their care providers “should be counselled about this risk and … should be aware of the signs of this condition and the fact that there is no known association between this outcome and any predictive risk factor.”