New mothers have very high levels of oxytocin, a hormone associated with touch, nurturing and especially breastfeeding, and so they will get very annoyed at anything that distracts from their nursing of their babies.
"This is a biological adaptation," said Meltzer-Brody.
"A lot of this stress may also have to do with role perception," she said. "There's the notion that mothers should be at home caring for the child more so than fathers, who work to provide for the family. These are stereotypes, but these societal influences are still there," Meltzer-Brody said.
Not all mothers ABC News spoke with reported they felt plagued by work guilt. Despite busy schedules and full-time jobs, several women said they could juggle their work duties and not feel as if they were neglecting work or home life.
Irina Baranov, 39, who works in marketing in Philadelphia, said that having flexibility in her schedule allowed her to align her work time with her kids homework and school time, which made the balance easier. Also, she and her husband have designated times when "phones/computers/BlackBerries are off," such as during dinner.
For the moms who haven't been able to align home and work so neatly, knowing that other moms feel the same guilt they do may help, Meltzer-Brody said.
"A lot of moms are reluctant to admit that they are having a hard time. If working moms had more support and understood that these feelings are common, they may feel less isolated," she said. "It would be more of a sisterhood of working moms."