Placenta Brain: the cognitive burden of pregnancy?

Ever had a case of 'placenta brain', or 'pregnancy stupidity'? Can carrying a foetus make you drop your cognitive bundle? Expecting women worldwide find themselves suddenly forgetful and absent minded. So why is there so little research into the phenomenon? Are hormones to blame, or the psychological burden of approaching mumhood? Does it have an evolutionary function? Libbi Gorr and others contemplate the hungry placenta..