A new study by scientists in the UK has shown that raging hormones during pregnancy not only prompt mood swings, but may also lead to a heightened ability to recognise threatening or aggressive faces.
This may have evolved because it makes would-be mums hyper-vigilant, yet it could also make them more susceptible to anxiety, according to the study.
Studies in the past have shown that a woman's ability to correctly identify fearful or disgusted facial expressions varies according to her stage of the menstrual cycle, with perception heightened on days associated with high levels of the hormone progesterone.
Since levels of progesterone and other hormones rise dramatically in late pregnancy, Rebecca Pearson and her colleagues at the University of Bristol in the UK conducted a study to find out whether the ability to read faces varies during pregnancy.
The researchers asked 76 pregnant women to assign one of six emotions to 60 computer-generated faces before the 14th week of pregnancy, and again after the 34th week, reports New Scientist.
They found that faces expressing happiness and surprise tended to be correctly assigned at both stages of pregnancy, but for faces expressing fear, anger and disgust, the accuracy rates were higher in late pregnancy.
According to researchers, this may increase the chance that the woman will spot potential threats to her and her foetus, and prime her to be hyper-vigilant once she becomes a mother.
However, it could have a disadvantage. Pearson points out that people with clinical anxiety are also better at identifying negative emotions in faces.
Pregnant women aren't clinically anxious, but 'they might interpret negative or emotional things around them in a slightly more sensitive way', she said.
The study has been published in the journal Hormones and Behaviour.