Severe uterine contractions in labor can trigger emotional disorders including postpartum depression in women during the puerperium. Numerous studies have shown that resting frontal electroencephalogram (EEG) asymmetry is closely related to depression. Therefore, the investigators hypothesize that the frontal alpha asymmetry in EEG during uterine contractions in the first stage of labor be associated with the risk level of postpartum depression. The objective of this research is to investigate, in a 1-year period, the incidence of postpartum depression in natural birth mothers in relation to frontal alpha asymmetry in EEG during uterine contractions and resting state.

Severe uterine contractions in labor can trigger emotional disorders including postpartum depression in women during the puerperium. It is characterized by lack of motivation and behavioral changes, potentially producing serious negative consequences for offspring.

In addition, EEG alpha asymmetry is one of the commonly studied biomarkers for depression. There are multiple previous studies regarding the symmetry of EEG in left and right brain hemispheres, especially at frontal electrodes. Besides, there are many other EEG indicators that predict depression which are also likely to be strong contributors to postpartum depression.

The objective of study is to investigate if there is any association between EEG alterations of uterine contractions in the first stage of labor and factors that are associated with postpartum depression.

Inclusion Criteria:

• parturient women with a singleton pregnancy;
• capable of understanding the research requirements and willing to cooperate with the study instructions;
• aged 18-45;
• American Society of Anesthesiologists(ASA) physical status I or II;
• right handed;
• not taking any drug known to influence the EEG;
• EPDS scale (Edinburgh Postnatal Depression Scale, EPDS) is used in the last prenatal examination in outpatient clinics , with scores < 10;
• informed consent is gained from all individual subjects taking part in the study.

Exclusion Criteria:

• history of neurological or psychiatric disease;
• personality disorder;
• cerebral disease;
• epidural anesthesia contraindication;
• multiparous pregnancy.

Participants will consist of parturient women who plan a vaginal delivery in Zhujiang hospital .