Male fetal pig lower urinary tract function in mid second and early third trimester of gestation

Routine use of ultrasound during pregnancy has emphasized the need for greater knowledge about normal and abnormal voiding function during fetal live. We describe the developmental changes in lower urinary tract function from the middle of the second to the early third trimester of gestation.

The study included 22 male fetal pigs of 13 pregnant Goettingen minipigs (gestational period 111 to 115 days) with 11 fetuses in the middle of the second (median 61.5 days, 0.55 of term) and 11 fetuses in the beginning of the third trimester of gestation (median 80 days, 0.72 of term). With the sow under isoflurane anesthesia catheters were placed in the bladder, rectum and amniotic cavity of the fetuses, and a flow probe was placed around the distal urethra. After the sow was at light sleep urethral flow, amniotic pressure, abdominal pressure and bladder pressure were recorded a median of 241 minutes.

The recordings of 14 fetuses were evaluable. In the middle of the second trimester the fetuses showed an almost constant dribbling with a median flow of 0.2 ml. per minute and a median of 4 concomitant bladder contractions per minute of median 3.5 cm. H2O (detrusor pressure). At the beginning of the third trimester the fetuses had periods of staccato flow (median 0.2 ml. per minute, staccato frequency 1 to 2 Hz.) on top of contractions (median 4 contractions per minute, median detrusor pressure 5.5 cm. H2O) with no flow between voidings.

Development of storage and voiding function in male pigs occurs between the mid-second and early third trimester of gestation, together with emergence of striated sphincter bursting activity, which interrupts flow in the urethra during the voiding phase.