A roundup of this week’s pregnancy-related scientific research and news:

The flu has hit harder and earlier across the nation this season. Boston has already experienced 700 cases of the flu – up from 70 cases last season – prompting the city's mayor Thomas Menino to declare a flu health emergency. Massachusetts has had 18 flu-related deaths so far, according to the state's Department of Public Health.

Pregnant women are among the groups considered the most vulnerable for catching the flu. A weaker immune system puts pregnant women at higher risk for more severe illness as well as birth complications. But experts say there’s no need to panic since there are many ways to protect against the flu.