What are the causes of oligohydramnios in 1st trimester?

OligohydramniOS in the first trimester can be caused by several factors, including fetal anomalies, such as renal agenesis or urinary tract obstructions, which impair urine production. Maternal conditions, such as dehydration or certain medications, can also contribute to low amniotic fluid levels. Additionally, issues with the placenta, such as placental insufficiency, may affect fluid dynamics. Early rupture of membranes can be another cause, although it's more common later in pregnancy.