Pregnancy

Pregnancy is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. In a pregnancy, there can be multiple gestations (for example, in the case of twins, or triplets).

Human pregnancy is the most studied of all mammalian pregnancies. Human pregnancy lasts approximately 9 months between the time of the last menstrual cycle and childbirth (38 weeks from fertilisation). A pregnancy is considered to have reached term between 37 and 43 weeks from the beginning of the last menstruation. Babies born before the 37 week mark are considered premature, while babies born after the 43 week mark are considered post-mature.

Perinatal period

Perinatal defines the period occurring "around the time of birth", specifically from 22 completed weeks (154 days) of gestation (the time when birth weight is normally 500 g) to 7 completed days after birth. Legal regulations in different countries include gestation age beginning from 16 to 22 weeks (5 months) before birth.

Postnatal period

The postnatal period begins immediately after the birth of a child and then extends for about six weeks. During this period the mother's body returns to prepregnancy conditions as far as uterus size and hormone levels are concerned.

Childbirth

Childbirth is the process whereby an infant is born. It is considered by many to be the beginning of the infant's life, and age is defined relative to this event in most cultures. A woman is considered to be in labour when she begins experiencing regular uterine contractions, accompanied by changes of her cervix — primarily effacement and dilation. While childbirth is widely experienced as painful, some women do report painless labours, while others find that concentrating on the birth helps to quicken labour and lessen the sensations. Most births are successful vaginal births, but sometimes complications arise and a woman may undergo a cesarean section. During the time immediately after birth, both the mother and the baby are hormonally cued to bond, the mother through the release of oxytocin, a hormone also released during breastfeeding.