Since the amniotic membrane was established during the embryonic period, the amniotic fluid secreted by the amniotic epithelium fills the amniotic cavity, creating a water environment, ensuring a relatively constant temperature, chemical composition, osmotic pressure and buoyancy environment, thereby providing a safe living environment for the fetus. In the late pregnancy, the amniotic fluid becomes viscous, and during delivery, it plays a role in expanding the uterus, flushing and lubricating the birth canal to facilitate the delivery of the fetus. The average peak time of pig embryo amniotic fluid is 67 days after pregnancy, which can be clearly seen on veterinary B-ultrasound. There are also reports that it reaches a peak at 75 days of pregnancy. The volume of human amniotic fluid shows a trend of increasing first and then decreasing. It is about 30ml at the tenth week, rising to 350ml at the 20th week, and reaching a peak of 1000-1500ml at 36-38 weeks. After that, it decreases by an average of 14ml per week, and can still maintain 500-1000ml at delivery.

BXL-V20 for sheep B-ultrasound

There are two sources of amniotic fluid: one is the secretion of the amniotic epithelium, and the other is derived from the metabolic products of the fetus. Absorption is by the amniotic epithelium on the surface of the placenta and umbilical cord, the surface of the fetal body, and by the fetus directly swallowing. It was found that the volume of amniotic fluid and urine changed significantly with the extension of pregnancy, but the most representative and clinically significant is the ratio of amniotic fluid to urine. The veterinary B-ultrasound observed that at 80 days of pregnancy, the volume of amniotic fluid was significantly higher than that of urine, and the ratio of the two was 3.85. This shows that before the second trimester, the fetus develops faster and has a relatively strong metabolism. At the same time, due to the immaturity of the fetus, the body surface area is small, the swallowing function is poor, and the placenta transport function is relatively imperfect, mainly absorbing nutrients, and the excretion of metabolites is relatively small, resulting in a relatively high amniotic fluid content. Veterinary B-ultrasound observed that at 100 days of pregnancy, the volume of amniotic fluid and urine increased significantly, but the gap between the two decreased, and the ratio of the two was 1.22. This shows that the metabolism of the fetus is gradually enhanced, the swallowing function is enhanced, the absorption of the body surface area is enhanced, and the nutrient transport function and metabolite excretion function of the placenta are also gradually increasing. Veterinary B-ultrasound showed that at 120 days of pregnancy, the urine content exceeded the amniotic fluid content, and the ratio of the two was 0.82. In addition to being related to the gradual maturity of the fetus, this may also be related to the fact that the total blood flow output from the fetal placental cotyledons at the end of pregnancy was lower than the total blood flow input from the uterine caruncle. Sheep B-ultrasound showed that at 140 days and full term, the volume of amniotic fluid and urine had become relatively stable, with the ratios of the two being 0.97 and 1.01, respectively. This shows that the relative changes in the content of amniotic fluid and urine can indirectly reflect the degree of maturity of placental function, and the placenta is mature around 140 days.

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