Ask any pregnant woman how she feels and often the answer will be one of exasperation. "Ugh, I feel fat; I'm so tired; I'm over it; I'm so hormonal and moody."

Everyone has bad days, especially during the long nine months of pregnancy. But for as many as 20 percent of pregnant women this normal mood shift can become a serious case of the pre-baby blues. Fortunately, Women can do many things to boost their mood and enjoy their pregnancy.

The statistics vary, but it is believed that antenatal depression affects between seven and 20 percent of pregnant women. And it is as common as the wider known condition, postnatal depression.

"Traditionally we have talked about post-natal depression and in the last five or so years … researchers like ourselves have become aware that a lot of the depression really is starting in pregnancy," explains Associate Professor Marie-Paule Austin, who heads the Royal Hospital for Women's Perinatal* Mental Health Clinic in Sydney. (*Perinatal is the umbrella term for both antenatal and postnatal depression).

During most pregnancies depression can creep up gradually and many of its symptoms, such as fatigue, are common , it can be difficult for health professionals and the women themselves to see it coming.

"It can be quite insidious and people just think they are tired or putting on weight or are a bit hormonal," explains Assoc Prof Austin, who is also affiliated with the depression research and education group the Black Dog Institute.

It is important to identify depression early because, without treatment, it can lead to postnatal and ongoing depression. In fact, up to 40 percent of women who experience antenatal depression develop postnatal depression if they don't receive treatment.