The lower part of uterus communicates with the vagina by a narrow cervical canal. Although the inner diameter of this portion of the anatomical structure varies considerably with age and number of vaginal deliveries, an average diameter of 3-5 mm. is too narrow to allow a variety of medical procedures reaching into the uterus, e.g. to insert a device, such as an IUD, to empty the uterus from products of conception, to remove abnormal inner layer of the uterus by suitable instrument, etc.
With increasing feasibility and availability of new methods for pregnancy termination, the non-traumatic and effective dilation of the cervix remains a major problem. The traditional method of enlarging the cervical canal employs various types of metal dilators. Such procedure require physician's skill and experience, and is often the only painful and most difficult part of abortion procedures. The popularity of metal dilators is declining mainly because of high incidence of cervical uterine injury.
Another method for enlarging the cervical canal uses laminaria tents or inserts i.e., dried sticks of a seaweed growing in cold ocean waters (Laminaria japonica). The laminaria inserts swell during several hours in a moist environment with a gradual increase in diameter of up to a value several times larger than the original diameter. The swelling thus applies a slowly increasing pressure onto the cervical canal, and such slow pressure is not painful and it is considered to be atraumatic to the cervical tissue and relatively convenient to the patient.
The use of Laminaria japonica has the following shortcomings:
(1) As most of natural materials, it cannot be perfectly sterilized.
(2) Its swelling rate is relatively low so that the insert is left in the cervix, as a rule, for about 24 hours. This is inconvenient to the patient (which must be either hospitalized or make two visits) and increases the probability of infection. Actually, there is an incidence of infection related mainly to the long period of insertion in the cervical canal.
(3) Relatively low swelling pressure causes that end protruding into uterus to swells faster, and more than the main part of the insert in the cervical canal thereby causing difficulty in subsequent removal.
(4) Uniform swelling and considerable decrease of mechanical strength of maximally swollen Laminaria japonica prevents successful removal in some cases as the protruding ends of the device are rather soft and slippery.
(5) Shortage of supply is another disadvantage.
(6) The diameter of the device is rather uneven and of the commercially available plant varies from about 2 to 4 mm. Often 3 to 6 of the laminaria are used simultaneously to obtain an adequate dilation, mainly in cases of advanced pregnancy termination.
(7) As the device is produced from the natural raw materials, it must be hand-made contributing to high prices.