A fetus is nourished and develops in the mother's uterus, residing in the amniotic sac throughout the pregnancy. During this time, the fetus is active and develops its circulatory, digestive, and urinary systems. So, how does a fetus excrete waste in the womb?
1. Fetal Urination in the Womb
According to research, a fetus begins to urinate as early as two months old, coinciding with the time it starts swallowing amniotic fluid and then excreting it. Essentially, the fetus drinks its own urine for about seven months in the womb.
As the fetus's circulatory, urinary, and kidney systems develop, they process the fetal blood and produce urine, which is then released into the surrounding amniotic fluid. Fetal urine is a significant source of amniotic fluid in the early months of pregnancy.
However, unlike feces, fetal urine in the amniotic environment is sterile and free of bacteria, posing no risk of infection to the fetus. Due to its crucial role, amniotic fluid is continuously replenished and renewed every three hours to ensure a healthy environment for fetal development.
2. Amount of Fetal Urine
Between the 31st and 34th weeks of pregnancy, the fetus excretes about 500ml of urine daily into the amniotic fluid. Amniotic fluid is a nutrient-rich environment with regenerative and exchange capabilities, playing a vital role in the fetus's development and survival in the womb. Thus, the fetus is continuously active and developing its digestive, circulatory, and urinary systems.
3. How Does a Fetus Excrete Waste in the Womb?
Fetal waste begins to accumulate gradually from the 24th week of pregnancy. This accumulation results from swallowing amniotic fluid, cell shedding, and digestive system activity. Meconium, the first stool, accumulates in the fetal intestines but is only excreted after birth during the first bowel movement, appearing dark green or black. In theory, the fetus only urinates and does not defecate in the womb.
However, about 12% of fetuses cannot retain meconium until birth and excrete it into the amniotic fluid. This can also occur if the fetus is overdue, with a mature digestive system capable of excreting meconium in the womb. In such cases, the amniotic fluid may appear green or slightly yellow. Generally, this does not harm the fetus while in the womb and poses no significant health risks. However, if meconium is excreted before the due date, it may indicate issues such as difficult labor, umbilical cord compression, oxygen deficiency, or infection.
4. What is Meconium Aspiration Syndrome?
Meconium aspiration syndrome is a condition to be aware of. Throughout the nine months of pregnancy, the fetus's lungs are filled with amniotic fluid. If the lungs contain meconium, it can pass through the trachea. During labor, if the fetus experiences prolonged oxygen deficiency, it may struggle to breathe and inhale meconium.
Inhaling meconium can block the airways, causing respiratory obstruction and reducing oxygen levels. Infants who inhale meconium are prone to respiratory distress and impaired gas exchange in the lungs. The chemical irritants in meconium can also cause pneumonia, infection, and inactivate surfactant (a substance that helps alveoli expand and facilitate gas exchange).
5. How to Prevent Meconium Aspiration Syndrome
Pregnant women should seek immediate medical attention if they notice any signs of labor or see dark green amniotic fluid. Regular prenatal check-ups are essential to monitor the pregnancy and address any issues promptly. Additionally, overdue pregnancies increase the risk of fetal meconium excretion before and during labor, so close monitoring from the 37th week onwards is crucial.
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