However, the duration of active first stage (from 5 cm until full cervical dilatation) usually does not extend beyond 12 hours in the first labour("primiparae"), and usually does not extend beyond 10 hours in subsequent labours ("multiparae").Dystocia of labour, also called "dysfunctional labour" or "failure to progress", is difficult labour or abnormally slow progress of labour, involving progressive cervical dilatation or lack of descent of the fetus. Friedmans Curve, developed in 1955, was for many years used to determine labour dystocia. However, more recent medical research suggests that the Friedman curve may not be currently applicable. Second stage: fetal expulsion
The expulsion stage begins when the cervix is fully dilated, and ends when the baby is born. As pressure on the cervix increases, a sensation of pelvic pressure is experienced, and, with it, an urge to begin pushing. At the beginning of the normal second stage, the head is fully engaged in the pelvis; the widest diameter of the head has passed below the level of the pelvic inlet. The fetal head then continues descent into the pelvis, below the pubic arch and out through the vaginal introitus (opening). This is assisted by the additional maternal efforts of "bearing down" or pushing, similar to defecation. The appearance of the fetal head at the vaginal orifice is termed the "crowning". At this point, the mother will feel an intense burning or stinging sensation. When the amniotic sac has not ruptured during labour or pushing, the infant can be born with the membranes intact.
Nuclear accidents
Beta burns were a serious medical issue for some victims of the Chernobyl disaster; from 115 patients treated in Moscow, 30% had burns covering 10–50% of body surface, 11% were affected on 50–100% of skin; the massive exposure was often caused by clothes drenched with radioactive water. Some firefighters developed beta burns of lungs and nasopharyngeal region after inhalation of massive amounts of radioactive smoke. Out of 28 deaths, 16 had skin injuries listed among the causes. The beta activity was extremely high, with beta/gamma ratio reaching 10–30 and beta energy high enough to damage basal layer of the skin, resulting in large area portals for infections, exacerbated by damage to bone marrow and weakened immune system. Some patients received skin dose of 400–500 Gy. The infections caused more than half of the acute deaths. Several died of fourth degree beta burns between 9–28 days after dose of 6–16 Gy. Seven died after dose of 4–6 Gy and third degree beta burns in 4–6 weeks. One died later from second degree beta burns and dose 1-4 Gy. The survivors have atrophied skin which is spider veined and with underlying fibrosis.The burns may manifest at different times at different body areas. The Chernobyl liquidators burns first appeared on wrists, face, neck and feet, followed by chest and back, then by knees, hips and buttocks.Industrial radiography sources are a common source of beta burns in workers. Radiation therapy sources can cause beta burns during exposure of the patients.