USMLE® Step 1 style questions USMLE
A 24-year-old gravida 1 para 0 woman at 27 weeks of gestation comes to the office for evaluation of a low amniotic fluid index discovered on a biophysical profile. The pregnancy has been complicated by gestational diabetes mellitus. The patient is currently on an insulin regimen. Fetal ultrasonography shows bilateral absence of the kidneys. The doctor explains to the mother that this is most likely due to aberrant interaction between the ureteric bud and metanephric mesenchyme. Which of the following structures does the ureteric bud give rise to under normal conditions?
Potter sequence exam links
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
Potter sequence is a rare disorder that is sometimes called oligohydramnios sequence—a term that helps define it because oligo- means low and -hydramnios means amniotic fluid.
So in Potter sequence there’s basically very little amniotic fluid and this makes the uterus a pretty hostile place for the fetus to grow.
Typically, around the 20th week of gestation, the kidneys, ureters, and urethra develop and start producing and excreting urine, and this urine becomes the major source of amniotic fluid.
Various conditions like renal agenesis, which is when one or both kidneys are missing, or atresia of the ureter or urethra, which is where those parts of the urinary tract are obstructed, can lead to an inability to produce or excrete urine and therefore leads to oligohydramnios.
Other common causes can include amniotic rupture, which is the leakage of amniotic fluid, or uteroplacental insufficiency, which is where there’s low blood flow from the placenta meaning the fetal organs—which includes the fetal kidneys—see less blood flow, which in turn leads to decreased urine production.
When there’s very little amniotic fluid, a couple of things happen as a result. First, amniotic fluid is crucial for the development of the fetal lungs, by both helping the airways physically stretch out as well as contributing amino acids like proline, which helps with the formation of connective tissue and collagen in the lung.
With less amniotic fluid, though, there’s pulmonary hypoplasia. Hypo meaning under, and -plasia means formation, so the lungs basically remain underdeveloped.
Not only that though, with less amniotic fluid, there’s less space in the amniotic sac, and so the fetus is literally compressed into a smaller space, which causes developmental abnormalities like a flattened face, wrinkly skin, widely separated eyes with epicanthal folds, low-set ears, as well as limb abnormalities like clubbed feet.
Potter sequence is the atypical physical appearance of a fetus or neonate resulting from oligohydramnios experienced in the uterus. POTTER itself is a mnemonic, and it stands for Pulmonary hypoplasia, Oligohydramnios, Twisted skin for wrinkles, Twisted face, Extremity deformities, and Renal agenesis.
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
- "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
- "Potter′s sequence" Journal of Clinical Neonatology (2012)
- "Special Imaging Casebook" Journal of Perinatology (2000)
- "The Potter Syndrome of Renal Agenesis" BMJ (1958)