Common symptoms include:

sudden-onset abdominal pain
contractions that seem continuous and do not stop
vaginal bleeding
enlarged uterus (disproportionate to the gestational age of the fetus)
decreased fetal movement
decreased fetal heart rate.Vaginal bleeding, if it occurs, may be bright red or dark.A placental abruption caused by arterial bleeding at the center of the placenta leads to sudden development of severe symptoms and life-threatening conditions including fetal heart rate abnormalities, severe maternal hemorrhage, and disseminated intravascular coagulation (DIC). Those abruptions caused by venous bleeding at the periphery of the placenta develop more slowly and cause small amounts of bleeding, intrauterine growth restriction, and oligohydramnios (low levels of amniotic fluid). Risk factors
Pre-eclampsia
Chronic hypertension
Short umbilical cord
Premature rupture of membranes
Prolonged rupture of membranes (>24 hours). Thrombophilia
Polyhydramnios
Multiparity
Multiple pregnancy
Maternal age: pregnant women who are younger than 20 or older than 35 are at greater riskRisk factors for placental abruption include disease, trauma, history, anatomy, and exposure to substances. The risk of placental abruption increases sixfold after severe maternal trauma. Anatomical risk factors include uncommon uterine anatomy (e.g. bicornuate uterus), uterine synechiae, and leiomyoma. Substances that increase risk of placental abruption include cocaine and tobacco when consumed during pregnancy, especially the third trimester. History of placental abruption or previous Caesarian section increases the risk by a factor of 2.3. Pathophysiology
In the vast majority of cases, placental abruption is caused by the maternal vessels tearing away from the decidua basalis, not the fetal vessels. The underlying cause is often unknown. A small number of abruptions are caused by trauma that stretches the uterus.
Teratomas of embryonal origin are most often found in babies at birth, in young children, and, since the advent of ultrasound imaging, in fetuses. The most diagnosed fetal teratomas are sacrococcygeal teratoma (Altman types I, II, and III) and cervical (neck) teratoma. Because these teratomas project from the fetal body into the surrounding amniotic fluid, they can be seen during routine prenatal ultrasound exams. Teratomas within the fetal body are less easily seen with ultrasound;  for these, MRI of the pregnant uterus is more informative. Complications
Teratomas are not dangerous for the fetus unless either a mass effect occurs or a large amount of blood flows through the tumor (known as vascular steal). The mass effect frequently consists of obstruction of normal passage of fluids from surrounding organs. The vascular steal can place a strain on the growing heart of the fetus, even resulting in heart failure, thus must be monitored by fetal echocardiography. Teratomas can cause an autoimmune illness called  N-methyl-D-aspartate (NMDA) receptor encephalitis. In this condition, the teratomas may contain B cells with NMDA-receptor specificities.After surgery,  a risk exists of regrowth in place, or in nearby organs. Pathophysiology
Teratomas belong to a class of tumors known as nonseminomatous germ cell tumor. All tumors of this class are the result of abnormal development of pluripotent cells: germ cells and embryonal cells. Teratomas of embryonic origin are congenital; teratomas of germ cell origin may or may not be congenital.