Treatment with aspirin or interferon is associated with up to ten-fold higher live birth rates in pregnant women with myeloproliferative neoplasms (MPN), research from Canada shows.

The findings, published in JAMA Open, are important as two trends – increasing maternal age in general and younger age at diagnosis of MPN – result in more women with the disorders either pregnant or planning a pregnancy.

A systematic review identified 22 studies of pregnant women with essential thrombocythemia or polycythemia vera treated with aspirin, unfractionated or low-molecular-weight heparin (LMWH), or interferon versus a comparison group. No studies of women with myelofibrosis met the inclusion criteria.

Together the studies comprised 767 women and 1,210 pregnancies and an overall live birth rate of 71.3% – lower than the expected rate of about 80% in the general population.

The live birth rate was 71.1% in women with essential thrombocythemia and 66.7% for polycythemia vera.

A meta-analysis found aspirin use during pregnancy, with doses ranging from 50mg to 300mg, was associated with higher odds of live births (OR 8.6).

Similarly, interferon, with or without aspirin or heparin, increased the odds of live birth compared with observation alone (OR 9.7).

LMWH alone (OR 6.0) or the addition of low doses of LMWH or unfractionated heparin to aspirin (OR 2.1) were not associated with significantly different odds of live births, the study authors said.

The pooled rate of any adverse events in the women was 9.6%, with preeclampsia most commonly reported (3.1%).

“Moderate-quality evidence suggests that the use of aspirin and interferon during pregnancy were associated with nearly 9- to 10-fold higher odds of a successful pregnancy than observation alone.”

“Maternal adverse events were uncommon and use of aspirin or interferon was not associated with difference in the odds of maternal adverse outcomes,” the researchers said.

While the gestational age at which to commence therapy has not been established, the authors said aspirin should be considered early in pregnancy to reduce the risk of first trimester miscarriages.

“The early addition of interferon to improve placental hypoperfusion may further improve pregnancy outcomes; however, further investigation with randomized clinical trials is needed to investigate this.”