referring now to the drawings , the details of preferred embodiments of the present invention are graphically and schematically illustrated . like elements in the drawings are represented by like numbers , and any similar elements represented by like numbers with a different lower case letter suffix . as shown in fig1 a and 1b , the intrauterine fetal monitoring electrode assembly 10 of the present invention is a thin , flexible strip 14 made of an insulating material . the flexible insulating strip 14 has a first side 16 , a second side 18 , an insertion end 20 , a connector end 22 , a length l and a width w . the length l of the flexible strip 14 ranges from about 4 . 0 cm to about 10 . 0 cm , and the width w from about 0 . 5 cm to about 2 . 0 cm . a metallic contact electrode 26 is fixed to each side of the strip 14 . the electrodes 26 are disposed on the two sides 16 & amp ; 18 of the insulating strip proximate the connector end 22 . as shown in fig2 the configuration , positioning and number of the electrodes 26 may vary , but each must electrically project to the connector end 22 of the flexible insulator strip 14 . an electrical connector cable 30 , comprising a distal end 32 and an insulating sheath 34 containing electrical leads 36 , is attached at its distal end 32 to the connector end 22 of the insulating strip 14 . the attachment of the distal end 32 to the insulating strip 14 is adapted to provide electrical connectivity between each electrode 26 and a separate electrical lead 36 disposed within the insulating sheath 34 of the connector cable 30 . the proximal end ( not shown ) of the connector cable 30 is adapted to be attachable to the input of a fetal monitor device , so that a separate electrical lead or wire 36 ( see fig3 ) connects each surface contact electrode 26 to a piece of fetal monitoring equipment ( not shown ). the piece of fetal monitoring equipment that the proximal end of the electrical connector cable connects to can be an electrode selector switch and / or a two lead to three lead adaptor ( e . g ., a body tissue impedance simulating circuit ). a grip feature 50 is included on one side of the insulating strip 14 at the insertion end 20 . the purpose of the grip feature is to provide a means for inserting the electrode assembly 10 through the cervical opening and into position between the tissue of the fetus and the uterine wall . the grip feature 50 may be a pocket for releaseably receiving a stylet guide ( not shown ), or simply a finger grip to facilitate positioning the electrode assembly by hand ( see fig1 b ). in use , as shown in fig4 the flexible strip 14 portion of the electrode assembly 10 is introduced into the vagina 40 ( e . g ., during vaginal exam ) and advanced through the dilated cervix 42 between the maternal uterine wall tissue 44 and the fetus &# 39 ; head 46 . a finger grip 50 fixed at the insertion end of one side of the flexible insulating strip 14 aids in the insertion of the electrode assembly 10 into position ( see fig4 ). the electrode assembly 10 may be held in place by surface features 54 , like “ fish scales ,” on either or both sides of the electrode strip 14 in combination with the pressure of the uterine sidewall 44 against the electrode strip 14 . the electrode assembly 10 comprises a thin , flexible electrode strip 14 having two sides 16 & amp ; 18 , and serves as an insulator separating the electrodes 26 on one side of the strip from those on the other side . the insulating electrode strip 14 may be made of any of a variety of flexible insulator materials to which a metal electrode may be fixed , such as rubber , latex and plastic . in a preferred embodiment , the electrode strip 14 is a polyester film on which it is possible to adhere or plate a conductive metal . mylar ™ ( dupont de nemours & amp ; co ., delaware ) is a commercially available polyester film that is a preferred electrode strip material , as the plating of conductive metal on to mylar ™ is already known in the art . however , any electrical conductor that can be fixed to the surfaces of the flexible strip 14 may be adapted for use as electrodes 26 in the present invention , including stainless steel . the insulating / electrode strip 14 has two electrodes 26 ( or two sets of electrodes ), one disposed on each of its sides 16 & amp ; 18 . the electrodes 26 may be disposed in various locations on the electrode strip 14 with a conductor portion of each electrode 26 leading to the connector end 22 of the strip 14 where it is connected to it own electrical lead 36 for connection to the input of the fetal monitoring equipment . either side 16 & amp ; 18 of the insulating strip 14 may have a plurality of electrodes 26 disposed on that side . one set of electrodes 26 can serve as signal electrodes 26 a , and the other set can serve as reference electrodes 26 b . ( see fig3 ). one side 16 of the electrode strip 14 contacts the maternal tissue 44 of the uterus and has the grip feature 50 disposed at its insertion end 20 . the other side 18 of the flexible electrode strip 14 contacts the fetal tissue 46 . the contact electrodes 26 on the side 16 of the flexible strip 14 that interface with the maternal tissue 44 typically serve as the reference electrodes 26 b , and the electrodes 26 on the other side 18 of the flexible strip 14 that interface with the fetal tissue 46 serve as the signal electrodes 26 a . the electrical connector 32 of an electrical connector cable 30 is attached to the connector end 22 of the flexible electrode strip 14 , and connects the electrodes 26 to the leads 36 of the electrical connector cable 30 . in one preferred embodiment , the connection between the strip 14 and the cable 30 is fixed , and the entire electrode assembly 10 is disposable . in an alternative preferred embodiment , the flexible electrode strip 14 is removable or detachable from the connector cable 30 , and is separately disposable . this latter embodiment wherein the flexible insulating strip 14 is reversibly detachable from the connector cable 30 allows the electrical connector cable 30 to be reused by attaching a new electrode strip to the connector cable 30 . as shown in fig3 the electrical connector cable 30 has an insulating sheath 34 containing electrical leads 36 . an electrical connector 32 at the distal end of the connector cable 30 is attached to the connector end 22 of the insulating strip 14 and adapted to connect the electrodes on both sides of the flexible strip to its respective electrical lead . this provides electrical continuity between each electrode 26 and a separate electrical lead 36 disposed within the insulating sheath 34 of the electrical connector cable 30 . the proximal end ( not shown ) of the electrical connector cable 30 is adapted to be attachable to an input of the fetal monitor equipment . as noted above , the electrodes 26 of the present invention are contact - type electrodes . the present contact electrodes 26 are noninvasive , relative to the implant - type electrodes discussed above , in that they interact at the surface of the tissue they contact , and do not impale the tissue as do implant - type electrodes . to minimize the electrode - to - tissue contact impedance , the electrodes 26 have a sufficient surface area . how much surface area is sufficient is readily discernable by one of ordinary skill in the art . certain prior ecg electrodes are about 1 . 0 cm circles . the length l and width w dimensions of the present flexible electrode strip 14 is more than ample to provide for electrodes 26 having surface areas equivalent to those currently practiced in the field . to further improve electrical characteristics of the electrode assembly 10 , the dimensions of the electrode strip 14 allow an electrode 26 on one side of the strip 14 to be laterally displaced from the electrode 26 on the other side of the strip to increase the range of distances that the electrodes 26 can be spatially displaced . because spatial displacement of the electrodes is not necessarily dependant on the thickness of the insulating strip 14 , the thickness of the strip may be made very thin , and the strip 14 itself very ribbon - like . a ribbon - like aspect of the flexible electrode strip 14 enhances the ability of the electrodes 26 on the strip 14 to securely contact the tissue to improve the contact impedance characteristics of the electrode assembly 10 . a mylar ™ insulator strip 14 with silver plated electrodes 26 particularly embodies these benefits . to further optimize the electrode - to - surface contact area and contact impedance characteristics of the electrode assembly 10 , sets of multiple electrodes 26 may be disposed on one or both sides of the insulator strip 14 . by using a switching circuit ( not shown ) on the input to the fetal monitoring equipment ( not shown ) the best positioned electrode 26 or combination of electrodes 26 in the set , may be selected to increase the effective surface area of the electrode 26 , reduce contact impedance or otherwise optimize the input signal the monitoring equipment . as shown in fig5 the tissue contacting surface of an electrode 26 may be coated with a conductivity enhancing material 60 , such as is known in the art and described above . while the above description contains many specifics , these should not be construed as limitations on the scope of the invention , but rather as exemplifications of one or another preferred embodiment thereof . many other variation are possible , which would be obvious to one skilled in the art . accordingly , the scope of the invention should be determined by the scope of the appended claims and their equivalents , and not just by the embodiments .
a disposable and noninvasive intrauterine fetal monitoring electrode assembly for monitoring fetal heart rate comprises an electrode strip for insertion into the uterus of a woman in active labor , between and in contact with the tissue of the uterine wall and the baby , and an interconnect cable for connecting the assembly to fetal monitoring equipment . the electrode strip comprises a flexible two - sided insulating strip having one or more electrodes disposed on each side of the strip . an electrical connector cable containing electrical leads provides electrical connectivity between each electrode and a separate electrical lead disposed within the connector cable to the fetal monitoring equipment . the electrode strip of the assembly includes a grip feature by which the electrode strip may be engaged to facilitate its positioning in the uterus .