Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. It is typically diagnosed by ultrasound when the amniotic fluid index (AFI) measures less than 5 cm or when the single deepest pocket (SDP) of amniotic fluid measures less than 2 cm. Amniotic fluid is necessary to allow for normal fetal movement, lung development, and cushioning from uterine compression. Low amniotic fluid can be attributed to a maternal, fetal, placental or idiopathic cause and can result in poor fetal outcomes including death. The prognosis of the fetus is dependent on the etiology, gestational age at diagnosis, and the severity of the oligohydramnios. The opposite of oligohydramnios is polyhydramnios, or an excess of amniotic fluid. Etiology
The amount of amniotic fluid available is based on how much fluid is produced and how much is removed from the amniotic sac. In the first trimester, the main sources of amniotic fluid are fetal lung secretions, transportation of maternal plasma across the fetal membranes, and the surface of the placenta. By the second trimester, the fetal kidneys start to produce urine which becomes the main source of the amniotic fluid for the remainder of the pregnancy.The development of oligohydramnios may be idiopathic or have a maternal, fetal, or placental cause. Maternal
Conditions such as preeclampsia, chronic hypertension, collagen vascular disease, nephropathy, and thrombophilia cause uteroplacental insufficiency.
A standard chemotherapy two-drug regimen (epirubicin plus ifosfamide) may be used in these cases. In place or combined with surgery and/or radiotherapy, severe and/or metastatic cases of UPS are commonly treated with epirubicin plus ifosfamide; doxorubicin alone or combined with ifosfamide, olaratumab, trabectedin, gemcitabine, or docetaxel;  cyclophosphamide, vincristine, doxorubicin, plus dacarbazine or cisplatin; cyclophosphamide, doxorubicin, plus dacarbazine; high dose methotrexate; or etoposide, ifosfamide, and cisplatin. These treatment regimens have been reported to lower local recurrence rates, prolong disease-free survival rates (i.e. time after treatment when no disease is detected), and increase overall survival rates (i.e. time after treatment to death from any cause). However, other studies report that the addition of radiotherapy and/or chemotherapy to surgical resection does not improve recurrence or overall survival rates; addition of radiotherapy to surgery improves local control of UPS tumors but not disease-free survival rates (i.e. time from treatment to recurrence of disease); and adjuvant chemotherapy and radiotherapy have no significant effects on local recurrence-free survival rates, metastasis-free survival times, and overall survival rates. Further studies are needed to define the best treatments for UPS tumors.In a retrospective study of 176 patients with localized UPS undergoing curative-intent treated with surgical resection or resection plus adjuvant treatment, disease-free survival rates at 120 months for patients with tumors in an extremity (leg or arm), heat/neck area, thorax, and abdomen/pelvis were about 70, 60, 50, and 0%, respectively; overall survival rates at 150 months for disease at these sites were about 90, 80, 75, and 35%, respectively.