Postnatal (Latin for after birth, from post, meaning after, and natalis, meaning of birth) is the period beginning immediately after the birth of a child and extending for about six weeks. Another term would be postpartum period, as it refers to the mother (whereas postnatal refers to the infant). Less frequently used is puerperium.
It is the time after birth, a time in which the mother's body, including hormone levels and uterus size, returns to a non-pregnant state. Lochia is post-partum vaginal discharge, containing blood, mucus, and placental tissue.
In scientific literature, the term is commonly abbreviated to PX. So that 'day P5' should be read as 'the fifth day after birth'. This is not to be confused with medical nomenclature that uses G P to stand for number of pregnancy and outcome of pregnancy.
Upon its entry to the air-breathing world, without the nutrition and oxygenation from the umbilical cord, the newborn must begin to adjust to life outside the uterus. Also starts his/her adaptation to extrauterine life, the most significant physiological transition until death.
Postpartum period in mothers 
A woman in the Western world delivering in a hospital may leave the hospital as soon as she is medically stable and chooses to leave, which can be as early as a few hours postpartum, though the average for spontaneous vaginal delivery (SVD) is 1–2 days, and the average caesarean section postnatal stay is 3–4 days. During this time, the mother is monitored for bleeding, bowel and bladder function, and baby care. The infant's health is also monitored.
The mother is assessed for tears, and is sutured if necessary. Also, she may suffer from constipation or hemorrhoids, both of which would be managed. The bladder is also assessed for infection, retention, and any problems in the muscles.
The major focus of postpartum care is ensuring that the mother is healthy and capable of taking care of her newborn, equipped with all the information she needs about breastfeeding, reproductive health and contraception, and the imminent life adjustment.
During the postpartum period, a woman may urinate out up to nine pounds of water. The extra fluid that her body has taken on is no longer needed, so the mother may note that her fluid output is disproportionate to her fluid input.
Early detection and adequate treatment is required. Approximately 25% - 85% of postpartum women will experience the "blues" for a few days. Between 7% and 17% may experience clinical depression, with a higher risk among those women with a history of clinical depression. Rarely, in 1 in 1,000 cases, women experience a psychotic episode, again with a higher risk among those women with pre-existing mental illness. Despite the wide spread myth of hormonal involvement, repeated studies have not linked hormonal changes with postpartum psychological symptoms. Rather, these are symptoms of a pre-existing mental illness, exacerbated by fatigue, changes in schedule and other common parenting stressors.
Postpartum psychosis (also known as puerperal psychosis), is a more severe form of mental illness than postpartum depression, with an incidence of approximately 0.2%.
East Asia 
In some East Asian cultures, such as Chinese and Vietnamese, there is a traditional custom of postpartum confinement known in English as doing the month or sitting the month (Mandarin zuò yuèzi 坐月子). Confinement traditionally lasts 30 days. Likewise, women in Japan frequently practice ansei, or peace and quiet, for a period of time after giving birth for the purpose of recuperating. This tradition combines prescribed foods with a number of restrictions on activities considered to be harmful. It is widely believed in many East Asian societies that this custom helps heal injuries to the perineum, promote the contraction of the uterus, and promote lactation.   
Traditionally, Greek mothers would spend 40 days confined at home with their infant after giving birth. At the end of the 40 days (the sarántisma, or "fortying"), the child was symbolically taken to church for the first time, where the mother asked for a special blessing on the conclusion of her puerperium. There are many modern theories seeking to justify this traditional practice, including weakness of infant immune systems, unimpeded establishment of breastfeeding, and the need for bonding time between parent and child.
Most traditional Indians follow the 40-day confinement and recuperation period also known as the 'Jaappa' (in Hindi). A special diet to facilitate milk production and increase hemoglobin levels is followed. Sex is not allowed during this time. In Hindu culture, the puerperium was traditionally considered a period of relative impurity (asaucham) due to the processes of childbirth, and a period of confinement of 10-40 days (known as purudu) was recommended for the mother. During this period, she was exempted from usual household chores and religious rites. The father was purified by a ritual bath before visiting the mother in confinement. In the event of a stillbirth, the period of impurity for both parents was 24 hours.
See also 
- parental leave
- Pre- and perinatal psychology
- Puerperal fever
- Pelvic girdle pain
- Early postnatal hospital discharge
- Postpartum depression
- "With Women, Midwives Experiences: from Shiftwork to Continuity of Care, David Vernon, Australian College of Midwives, Canberra, 2007 ISBN 978-0-9751674-5-8, p17f
- Dobson, V.; B. Sales (2000). "The Science of Infanticide and Mental Illness". Psychology, Public Policy and Law 6 (4): 1098–1112. doi:10.1037/1076-8922.214.171.1248.
- Effect of Alcohol consumption on Maternal lactation characteristics during ‘doing-the-month’ ritual
- Ayuvedic Postpartum Healing Tips
- Ayurvedic diet for de-stressing postpartum mothers
- Lactogenic Foods and Herbs
- GUIDE TO RITUAL IMPURITY - What to do at the junctions of birth and death
- New born Care
- eMedicine: Normal and Abnormal Puerperium
- Patient UK: Postnatal Care (Puerperium)
- Postpartum Social Awareness
- Discovery Health's Postpartum Planning Tool guides you through the mysteries of motherhood and babyhood from birth to 12 weeks.
- Pregnancy & Childbirth
- NHS Choices Birth to Five Planner: Postnatal post-traumatic stress disorder