Dr Signal said the unpublished data suggested sleep deprivation could play a part in the risk of developing depressive symptoms, which could lead to more significant mood or anxiety disorders.
"It may also be important in determining the need for medical intervention at birth," Dr Signal said.
Disrupted sleep patterns are associated with a bunch of pregnancy problems including a higher chance of needing a C-section, longer labor and increased probability of gestational diabetes, Dr Signal said.
There was also evidence of ethnic differences in some, but not all, aspects of sleep in late pregnancy.
Maori were more likely to report symptoms of sleep disorders, including breathing pauses, period limb movements, daytime sleepiness and what's known as as 'long-sleep' (more than nine hours in 24).
A total of 407 Maori women and 737 non-Maori women completed the study between 35 and 37 weeks of pregnancy, answering questions over the phone one month to six weeks after birth, and filling out another questionnaire at 12 weeks.
The study shows how important sleep was for pregnant women and the health of her growing baby, Dr Signal and Dr Paine said.
"If you feel sleepy during the day and are able to nap, then do so. Don't do this if it makes it harder for you to fall asleep at night. But make getting enough sleep one of your top priorities."
