During sterile speculum examination, ruptured membranes are diagnosed if amnionic luid pools in the posterior fornix or clear fluid lows from the cevical canal. lthough several diagnostic tests for [he detection of ruptured membranes have been recommended, none is completely reliable. If the diagnosis remains uncertain, another method involves pH determination of vaginal luid. The pH of vaginal secretions normally ranges from 4.5 to 5.5, whereas that of amnionic luid is usually > .0. The use of the indicator nitrazine to identiY ruptured membranes is a simple and fairly reliable method. Test papers are impregnated with the dye, and the color of the reaction between these paper strips and vaginal luids is interpreted by comparison with a standard color chart. A pH above 6.5 is consistent with ruptured membranes. False-positive test results may occur with coexistent blood, semen, or bacterial vaginosis, whereas false-negative tests may result with scant luid.
Other tests to identiY amnionic luid include arborization or ferning of vaginal luid, which suggests amnionic rather than cervical luid. Amnionic luid crystallizes to form a fernlike pattern due to its relative concentrations of sodium chloride, proteins, and carbohydrates. Detection of alpha-fetoprotein in the vaginal vault has been used to identiY amnionic luid (Yamada, 1998). Although rarely required, identiication may also follow injection of indigo carmine into the amnionic sac via abdominal amniocentesis. Last, speciic amnionic luid proteins can be sought using point-of-care assays. These include AmniSure, which binds placental alpha microglobulin-1, and ROM Plus, which detects insulin growth factor binding protein-1 plus alpha-fetoprotein (Doret, 2013; Igbinosa, 2017).
The degree of cervical facement relects the length of the cervical canal compared with that of an unefaced cervix. When the length of the cervix is reduced by one half, it is 50-percent efaced. When the cervix becomes as thin as the adjacent lower uterine segment, it is completely, or 100-percent, efaced.
Cervical dilation is determined by estimating the average diameter of the cervical opening by sweeping the examining inger from the margin of the cevical opening on one side to that on the opposite side. The diameter traversed is estimated in centimeters. The cervix is said to be fully dilated when the diameter measures 10 cm, because the presenting part of a term-size newborn usually can pass through a cervix this widely dilated.
he position of the cervix is determined by the relationship of the cervical os to the fetal head and is categorized as posterior, midposition, or anterior. Along with position, the consistency of the cervix is determined to be soft, irm, or intermediate between these two.
heetal station, that is, the level of the presenting fetal part in the birth canal, is described in relationship to the ischial spines. These spines lie halway between the pelvic inlet and the pelvic outlet. When the lowermost portion of the presenting fetal part is at the level of the spines, it is designated s being at zero (0) station.