Retrospective Investigation of Presence of Urobilinogen and Maternal Weight Loss as Indications of Impending Parturition in the Term Gravida

Rationale/Background:

This study is a retrospective review of records which examines the possibility of two markers for the onset of active labor (contractions which result in a change in the uterine cervical dilatation) on routine clinical prenatal assessment. The markers in question are an elevation of urobilinogen on routine dipstick and slight maternal weight loss. An apparent clinical correlation between the presence of urobilinogen, maternal weight loss and onset of active labor has been observed in our patient population. Our hypothesis is that these markers in the term gravida are an indication of delivery within a week of their appearance on routine prenatal evaluation. Should a correlation exist, the clinician would have a relatively inexpensive way of identifying patients that could deliver within the week and could possibly predict those patients that would have success with induction, as the normal labor process may have begun. The purpose of this study, then, is to search existing clinic and hospital records for answers to the following two questions: (1) Do pregnant women who are at least 37 weeks gestation and who have an increase in urobilinogen on urine dipstick at a prenatal appointment have a statistically significant shorter average time before going into active labor than their negative counterparts? (2) Do pregnant women who are at least 37 weeks gestation and who show a modest weight loss between two prenatal appointments have a statistically significant shorter average time before going into active labor than their counterparts who did not lose weight? In humans, the signals that initiate labor are not completely understood. While many theories have been explored, an exact pathway has not yet been determined. Urobilinogen is formed from conversion of conjugated bilirubin in the intestine by bacteria. A fraction of the urobiliogen is then reabsorbed into the bloodstream and filtered by the kidneys, becoming a colorless component of urine. Normally, only 1-4 mg of urobilinogen is excreted in the urine per day. Hemolytic processes, hepatocellular damage, and cholestasis can elevate urobilinogen in the urine. Routine dipstick tests have a normal urobilinogen range of 0.2 to 1 mg/dl (1). In this study, we will examine the urine dipsticks for an increased change in the urobilinogen levels within the last two prenatal appointments prior to delivery.

No previous studies could be located regarding a link between an elevation in urobilinogen and/or minor maternal weight loss and parturition, labor, onset. There have been studies to suggest rationale for our clinical observation, however. Estrogens and progesterone both play a role in the growth and contractility of uterine myometrial cells. Progesterone tends to promote uterine relaxation, hence the name "pro-gest...". In most species, progesterone levels dramatically fall, a 'withdrawal', prior to the onset of labor. However, in human and higher level primates, the progesterone and estrogen levels are both elevated in later gestation and during parturition. The "withdrawal" in humans, therefore, may be mediated by changes in the myometrial responsiveness to progesterone (2).

Estrogens induce myometrial contractility. Estriol is the most abundant estrogen during pregnancy and is produced by the placenta. It first appears at approximately the ninth week of gestation from the last menstrual period (3). Plasma concentrations of this estrogen increase throughout gestation along with those of estrone and estradiol (3,4,5). In the weeks preceding parturition, concentrations of estriol dramatically increase and continue to rise until birth (6). Estriol's roles include preparing uterine tissues for contraction and possibly signaling parturition in higher primates and humans (3,4,7,8,9,10). A rise in estriol, which can be monitored in saliva, has been shown to precede parturition, regardless of whether labor begins preterm, at term, or postterm (11,12).

Estrogens' effect on the liver has been studied extensively. The active transport of biliary components in the canaliculi is impaired by estrogen (13). The pregnant state can cause some changes in bile acid production and secretion, presumably due to the higher levels of estrogen, but also because of progesterone's effect on GI motility. This can lead to a mild subclinical cholestasis. Studies have shown conflicting evidence as to whether there is an increase in bile acid levels during pregnancy. As estrogen increases are known to induce a cholestasis, and urobilinogen levels increase in cholestasis, our hypothesis is that the increase in estrogen levels within the last week of pregnancy may slow the clearance of bile even further yielding the rise in urobilinogen levels noticed on routine dipstick.