Patient's question:
Hello Doctor!I just came back from the hospital because of low amniotic fluid, and the doctor ordered a fetal systematic ultrasound. He said he was concerned about potential problems with the baby's urinary system. However, the 3D ultrasound I had done two days ago showed that both the baby's kidneys and bladder are normal. The doctor mentioned that the reasons for low amniotic fluid could be issues with the urinary system or problems with the placenta. I feel that since the baby's kidneys and bladder are normal, there shouldn't be a significant risk of urinary system problems. So, I would like to understand this better: what is the likelihood that my baby has urinary system issues under these circumstances? Please help me, expert doctor. Thank you very much. First question.
Doctor's answer:
Hello:Due to the incomplete understanding of the mechanism of amniotic fluid production and circulation, there are many cases of oligohydramnios with unknown causes. Clinically, the following conditions are commonly observed.
1. Fetal malformations such as congenital renal agenesis, renal hypoplasia, ureteral or urethral stenosis, etc., can lead to reduced or absent urine production, resulting in oligohydramnios.
2. Postterm pregnancy In postterm pregnancy, placental function declines, leading to insufficient perfusion and fetal dehydration, which causes oligohydramnios. Some scholars also suggest that in postterm pregnancy, fetal overmaturation increases the sensitivity of renal tubules to antidiuretic hormone, resulting in reduced urine output and oligohydramnios. The incidence of oligohydramnios caused by postterm pregnancy ranges from 20% to 30%.
3. Intrauterine growth restriction (IUGR) Oligohydramnios is one of the characteristics of intrauterine growth restriction. Chronic hypoxia causes fetal circulatory redistribution, primarily supplying the brain and heart while reducing renal blood flow. This leads to decreased fetal urine production and subsequent oligohydramnios.
4. Amniotic membrane lesions Electron microscopic observation shows that the amniotic epithelial layer becomes thin in cases of oligohydramnios, with atrophic epithelial cells, short and coarse microvilli, swollen tips, reduced numbers, and squamous metaplasia. The rough endoplasmic reticulum and Golgi complex within the cells also decrease, as do desmosomes and hemidesmosomes between the epithelial cells and basal membrane. It is believed that some cases of unexplained oligohydramnios may be related to amniotic membrane lesions themselves.