Obstetrical History: Labor Induction Series: Rupturing Membranes

Women who need to be induced have to have some treatment to get them into labor, and physicians have clung on to the technique of rupturing a patient's members for at least the past 2000 years! Rupturing the membranes is a technique called Amniotomy, or "artificially rupturing the membranes" (AROM).
Soranus Epesius, Roman 103 A.D., performed AROM digitally or with a scalpel after the patient urinated, then he went on to augment with a honey oil enema, and had egg white introduced vaginally, primary to augment labor. Likely it was just the rupturing of membranes that was the key step.

In the modern days we have realized that there are many reasons to delay labor until term, but even in the mid-18th century the amniotomy (AROM) was introduced in the  to induce labor before full term to prevent the baby from not being able to deliver due to what is known as cephalopelvic disproportion (a misfit between the baby and the pelvis. Since then, AROM has had periods of varying popularity. Amniotomy, more than any other method of induction involves a firm commitment to delivery, once we rupture a patient's membranes, which is the normal barrier to infection, we have committed to making sure the patient does deliver. But, the main disadvantage of amniotomy to induce labor is the unpredictable interval from membrane rupture to the initiation of labor and delivery. Later in the 18th century, George Macauley advocated inducing labor to prevent dystocia due to pelvic contraction. Thomas Denman proposed the use of low amniotomy, or the "English operation", to induce labor only to avoid disproportion and to save the life of the fetus or mother. In Denman's 1794 textbook, An Introduction to the Practice of Midwifery, Denman asserted a conservative view that focused on the reliance on natural processes of labor, but recognized that rupture of membranes may be required in some circumstances.

The membranes have two layers, the amnion and the chorion, if either ruptures there is some fluid leak, but not until there is a full rupture of the membranes does fluid pour out of the cervix. The rupture can be performed at the opening of the uterus which is the cervix, or higher. During the first half of the 19th century, Hamilton advocated the use of high amniotomy, using a rubber catheter stiffed with a silver wire, in an attempt to reduce the high infection rates after amniotomy. However, in the mid 1800s, artificial rupture of membranes to induce labor fell into disuse because of the inconsistency and the unfortunate tendency to produce infection in either mother or baby.

But as a low cost and relatively effective method of inducing labor the use of low amniotomy re-surged slowly during this century. Many obstetricians hesitate to puncture the membranes in a woman in active labor on her own because they believe the amniotic sac serves as the wedge that encourages cervical dilatation. They also believed membrane integrity was necessary for cervical dilatation to progress and to prevent cord prolapse. Artificial amniotomy was reintroduced to American physicians between 1928 and 1930 by the works of Jackson, Slemons, Guttmacher, and Douglas. Their reports met widespread skepticism and debate. As it wasn't until the late 1980s that there was the widespread availability of ultraounds to confirm the size and lie of the baby many obstetricians and midwives feared that errors in judging presentation would follow its use and that the number and severity of injuries to the birth canal would increase. They also believed that elective amniotomy would increase the incidence of puerperal  (around birth) infection and fetal mortality as a result of cord prolapse and/or complications of premature placental separation. Now we know that it's unlikely that the placenta would ever separate prematuraly due to an obstetrician rupturing the membranes, and unless the baby is breech or transverse or very high in the pelvis the cord dropping is not likely either.

In the 1930s, the great obstetrician Eastman dispelled the notion of dry labor with evidence that amniotomy accelerated labor. Eastman found labor was 73% shorter in women who had amniotomy compared with women who did not. As a recognized leader who set standards many adhered to in his well written textbook Eastman listed three conditions necessary before artificial rupture of membranes should be performed: (1) the lowest part of the head must be at or below the level of spines; (2) the patient must be near or past her expected date of confinement; and (3) the cervix must be soft and the canal less than 1 cm. long (this translates into about 50% thinned out). When the conditions Eastman set forth were ignored, as reported by Plass in 1937, amniotomy could be performed, and labor would be brought on, but at great cost since he showed that ignoring these principals the obstetrician would find that the fetal mortality rate increased. In more than 600 patients in whom amniotomy was performed but Eastman's conditions were ignored, prolapsed cord occurred in 1% compared with approximately 0.3% when the head was well down where it should be (engaged). Eastman thought this was important because it demonstrated that amniotomy could be used in exceptional cases even though the head is not engaged  (down in the pelvis) and the cervix not effaced, but the increased risk to the fetus must be known.  for more on Eastman's thoughts read Clinical Obstetrics and Gynecology; Amniotomy to Induce Labor; 1995, pages 246-248. With more obstetricians adhering to the principals, and preforming AROM more safely, and the popularity of induction by the 1950s, amniotomy became more common after a clinical series overseen by Nixon. (Clinical Obstetrics and Gynecology; Laube article, page 462).


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