CONTRACEPTION VAS DEFERENS OCCLUSION BY PERCUTANEOUS INJECTION OF POLYURETHANE ELASTOMER PLUGS: CLINICAL EXPERIENCE AND REVERSIBILITY Zhao Sheng-cai Shanxi Provincial People's Hospital, Taiyuan, People's Republic of China
ABSTRACT
A non-incision method of vas occlusion based on the percutaneous injection of polyurethane elastomer solution to form plugs is described. The results are based on clinical experience in 12,000 men in which only 56 cases of minor complications were recorded. Follow-up of 500 men for up to 3 years demonstrated an azoospermia rate of 98%. Plugs have been removed from 86 men and, to date, 51 have made their wives pregnant. In those from which the plugs have been removed for more than 1 year (n- 31), the pregnancy rate is 100%. INTRODUCTION Occlusion of the vas deferens by ligation is now in widespread use as a contraceptive method (1). As normally practiced, it requires a skin incision and some dissection of the vas deferens itself. Although several studies have shown that, under optimal circumstances, surgical vasectomy can be reversed with varying success in terms of pregnancy outcome, the operation of vasovasostomy requires skill and experience in microsurgery (2, 3). For this reason, surgical vasectomy is only offered in Family Planning progammes as an irreversible means of male fertility regulation. It has been recognized for some time that two main factors limit the acceptibility of vas occlusion: one is the necessity for a skin incision, which is unacceptable in some cultures; and the other is the lack of certain reversibility should the family circumstances require this. Amongst many attempts to develop simplified methods to overcome these limitations, research in China, which started in 1970, has led to two major technical improvements: the isolation and ligation of the vas through a puncture (non-scalpel) opening in the skin; and the development for the percutaneous of a technique injection into the vas lumen of sclerotising and other agents through a hypodermic needle (4-7). The present report describes a modification of the method of percutaneous injection which has been used for the introduction into the vas deferens of medical-grade polyurethane elastomer to form a plug ir? z&i&. This method has been in clinical use in China since 1983 and preliminary reports have been given (7, 8). The overall efficacy is high, complications are few and there is accumulating evidence that, in the circumstances examined so far, removal of the plugs leads to recovery of fertility. Submitted for publication July 5, 1989 Accepted for publication January 29, 1990
MAY 1990VOL. 41 NO. 5
463
CONTRACEPTION MATERIAL!3 ANDMIZTHODS A.
Hedicel_ade
oolyurev
Two solutions must be mixed in equal volumes to form the Solution A is formed by the co-polymerization of polytetraplugs. methylene-ether glycol (i~LW.1000) with toluene-2,4-diisocyanate to form a pre-polymer linked by carbamate. Solution B is a chain extender ma& from methylene-bis-ortho-chloroaniline, a catalyst a solvent. Both solutions are liquid at ambient temperature. and They are mixed in equal volumes in a In1 glass syringe just before after which they form a smooth elastomer plug by chain injection, extension. The plug has a Shore hardness of 82-84, 45% elasticity tearing strength of 76-77 kg/cm. B.
The ooeration
for oercutaneous
wection
and a
in man
The present clinical experience is reported for 12,000 men who received the vas occlusion procedure in the period 1983-1987, the majority of whom (87%) were rural farm workers. They were aged 25-50 years, the majority (83.8%) being 25-35 years of age. All had fathered children, the majority (73.2%) having two children. The procedure is an adaptation of that described before (4-6) and is conducted under full aseptic procedures and local procaine anaesthesia. The vas deferens of one side is gripped through the skin by the vas-fixation lifted and an 8-gauge clam9 (Fig.W. (0.8mm diameter) hypodermic needle used to puncture the vas in the direction away from the testis (Fig. 2). This needle is then removed and a 6-gauge (0.6mm) blunt-ended needle inserted into the vas through the channel created by the puncture needle. Fig. 1A
Fig. 16
Atraumatic vas-fixation CkImP
F
T
Circular screw clamp
10 mm
I
!i!i!Y 3mm 0.5 mm
m
t
5mm
91I
ml
7mm
i
Fig. 1. Special instruments.
454
MAY 1990 VOL. 41. NO. 5
CONTRACEPTION Various
tests are used to verify that the needle tip is in the lumen: air injection into a finger-occluded distal section of the vas; the infusion of 5 ml 0.05% congo red (5 ml 0.02% methylene vas). There should be no subcutaneous blue in the contralateral emphysema following the first test or subcutaneous fluid following the second. When both vas deferens have been prepared in this way, 3 ml procaine solution is injected through each needle for its spennicidal action and a specially designed circular screw clamp
Fig. 2. Insertion of the puncture hypodermic
Fig.
3.
Position
MAY 1990 VOL. 41 NO. 5
of
screw
clamp
needle into the vas (6).
during
injection
(P., plug).
455
CONTRACEPTION applied to the scrotal skin to surround (diameter 1 cm; Fig.lB) the portion of the vas enclosing the tips of the injection needles Residual fluid is sucked out of the needle, the needle (FLg. 3). and then a lml glass syringe containing an equal mixture of dried, B is attached. A screw-plunger syringe solution A and solution holder is then applied to the syringe enabling 0.16 - 0.22 ml of elastomer to be injected smoothly through the needle. the viscous injected is adjusted according to the size of the vas The volume deferens and to achieve a bulge in the occluded portion of the injected in turn. The polymerization takes l-3 vas. Each vas is min although 24 hr is needed for complete setting. The subject is asked to urinate at the conclusion of the operation. If dye had been injected previously and the urine is coloured browu, the hjections were bilaterally successful; if the usual colour, both sides were unsuccessful; orange or green colour indicates faihre on one side or the other. Subjects are advised intercourse for 1 month. C.
The oneration
for ulue
to
rest
for 24 hr and
to abstain
from
removal
Permission by the State FamLly Planning Commission of the People's Republic of China was given for the removal of the plugs from 86 men. Their ages ranged from 30 - 35 years and the plugs had been in place for 3 months - 4 years. There are two groups according to length of time since removal of the plugs: group 1 l-2 years since removal; group 2 (n-55), 1-12 months since (n-31), removal. The scrotal prepared and skin is local procaine anaesthesia admincstered exactly as for the procedure for percutaneous injection of clamps (Fig.lA) the vas. Vas-fixation are placed on either side of the vasal segment containing the A short (about 1 cm) incision, not quite through the skin, plug. is made with a hand-held scalpel blade. A pair of sharp haemostat forceps are used to dissect through the skin and around both sides of the vas. The vas-fixation clamps are then transferred to the exposed vas on either side of the occluded section and the vas incised longitudinally (0.5-l cm) over the plug. This is loosened from its attachments to the mucous membrane and then removed with forceps (Fig.4). Usually the incision in the vas does not require a suture although the skin incision does.
Fig.
4. A polyurethane
456
elastomer
plug
after
removal
(scale:
10 mm).
MAY X390VOL. 41. NO. 5
CONTRACEPTION
RESULTS A.
CJQ
56 cases of complications during the first year of There were follow-up amongst the 12,000 men in this report. Of these, 47 were attributable to local infection and 9 to a local haematoma. There were no residual problems in 2.600 men followed-up for 3 years and in 1,000 men followed-up for 5 years. None of the subjects complained of epfdidymal swelling or pain or of any change in sexual function or libido. Of the 12,000 men who received the vas occlusion procedure in the period 1983-1987, the first 500 who accepted to provide semen samples by masturbation were examined after 1 year. Of these, 490 were azoospermic, 5 were severely oligozoospermic with less than 4 million spermatozoa per ml, 2 had sperm concentrations of 4-20 million per ml, and 3 had concentrations exceeding 20 million per ml. The azoospermia rate was therefore 98%. A similar efficacy rate persisted for 100 men who agreed to provide semen after 2 and 3 years of vas occlusion. B.
ei R versib lit
The removal of polyurethane plugs from 86 men has so far resulted in pregnancy of the wives of 51. The results from the two groups established according to the length of time since removal of the plugs, i.e. exceeding 1 year (Group 1, n-31 ) or less than 1 year (Group 2, n-55 ) are shown in the Table. All the wives of the men of Group 1 became pregnant within 1-2 years of reversal of vas occlusion when the semen of most men contained sperm in the normal concentration range. In Group 2, the time since reversal ranged from only 1 month to 1 year. Nevertheless, 37 men produced ejaculates containing sperm at concentrations of 5 (11 men) and 5-20 (26 men) million per ml and 20 wives have become pregnant.
Table Recovery of sperm in the ejaculates of two groups of men from whom the polyurethane plugs have been removed for more than and less than 1 year and the occurrence of pregnancy in their partners
Duration Gou 2
n
occlusion
1 2
31 55
2-4 3/12-l
MAY 1990VOL.
41 NO. 5
(year)
Sperm coDcentration 5-20
l-2 1/12-l
11
6 26
Pregnancy
O-100
no
25 -
31 20
100 36
457
CONTRACEPTION To date, 38 babies have been born, of which 18 are female and 20 male. All babies were normal at birth and no post-natal abnormalities have arisen. The oldest child fathered following vas reversal is now 5 years 8 months. DISCUSSION The percutaneous injection of polyurethane elastomer to form plugs ti g&~ has been accepted by approximately lOQ,OOO men to date and offers a method of vas occlusion which has good efficacy, a low incidence of complications and the possibility of successful reversal. There is a need for skill and practice to achieve percutaneous cannulation of the vas deferens and training schemes have been established for this purpose. The plug formed by the polyurethane elastomer was similar in and elasticity hardness to the vas deferens itself and the subjects did not have any awareness of its presence. The material apparently caused no local or general side effects. When injected in sufficient amount, the polyurethane elastomer formed a plug which maintained its position within the vas and was not moved by peristalsis. Animal toxicity studies suggest that the materials are non toxic (unpublished observations). There is good evidence that the removal of the plugs by the described leads to successful reversibility in simple operation terms of pregnancy outcome. The results available to date suggest that 100% reversibility may occur within 2 years of removal of the is equivalent to the This rate of return to fertility plugs. rate for couples in which both partners have expected pregnancy established proven fertility (9). It should be noted, however, of vas occlusion before removal is less than 4 that the duration years (Table). The success rate of the vasovasostomy operation is reduced when the duration of vasectomy is long (1, 2), althdugh Silber proposes that 'open-ended' vasectomy significantly improves of reversal (to 82%; 3). Future studies will attempt the success the success of reversal following periods of vas to monitor occlusion by plugs of more than 4 years. In conclusion, it is proposed that the non-incision, percutainjection of polyurethane elastomer provides a non-traumatic neous of vas occlusion with several advantages over surgical method It is likely to be more acceptable in some cultures in vasectomy. the world and the possibility of easy reversal could lead to widespread acceptability.
ACKNOWLEDGEMENTS I wish to express my gratitude to Professor Wu Jie-ping who throughout this work. The following served as consultant assisted in various ways: Associate Professors Peng colleagues Shao-bang and Li Guang-jia (chemistry); Professor Tan Pei-jiao
456
MAY 1990 VOL. 41. NO. 5
CONTRACEPTION Long-quan (pathological Associate Professor Yang (toxicology); Yi-he (clinical and Lian Drs. Li Qing-lu examination); assistants). Thanks are also due to Dr. Bianxi Feng for data for his drawings. I am and to Engineer Liu Hou-jun analysis grateful to the State Family Planning CoPPmission and the Shanxi I owe a special Provincial Government for their financial suport. to Dr. G.H.H. Waites. WHO Special Programme of debt of gratitude and Research Training in Human Reproduction Research, Development who revised my draft manuscript for publication.
REFERENCES 1.
Huber DH, Hong S, Ross JA. The international experience with vasectomy. In: Zatuchni GI. Goldsmith A. Spieler JH, Sciarra advances and future prospects. eds. Male contraception: JJ. Philadelphia: Harper and Row, 1986:7-18.
2.
Lee HY. A 20-year experience with vasovasostomy. 136:413-415.
3.
after vasovesostomy for vasectomy Silber SJ. Pregnancy reversal: a study of factors affecting long-term return of fertility in 282 patients followed for 10 years. Human Reprod 1989;4:318-322.
4.
Li The technique Shun-qiang. Chongqing Medicine 1973;3:7-12.
5.
Wu Jie-ping. Contraception by injection of 5% sodium morrhuate into the epididymides. In: The techniques of birth control. Shanghai: Shanghai Publishing House, 1979:242.
6.
Zhu Jin-bo. Ten years clinical study on Li Shun-qiang. for male sterilization. In: Qian percutaneous vas occlusion GMH eds. Advances in Fertility Regulation in the SZ, Waites The People's Medical Publishing House, 1985: Male. Beijing: 75-79.
7.
Chemical vas-occlusion in the People's Republic Xiao Bilian. of China. In: Diczfalusy E, Bygdeman R, eds. Fertility Serono Symposia Publications: Regulation Today and Tomorrow. Raven Press, 1987; 36:265-274.
8.
on reversible blocking Zhao Sheng-cai. Research spermatic duct using injected MPU. Reprod Contracept 12-16.
9.
Lenton EA, Weston GA, Cooke ID. apparently normal couple with a Fertil Steril 1977; 28:913-919.
MAY 199OVOL. 41 NO. 5
of
chemical
vas
J Urol 1986;
occlusion.
of the 1986; 6:
Long-term follow-up of the complaint of infertility.
ABSTRACT
A non-incision method of vas occlusion based on the percutaneous injection of polyurethane elastomer solution to form plugs is described. The results are based on clinical experience in 12,000 men in which only 56 cases of minor complications were recorded. Follow-up of 500 men for up to 3 years demonstrated an azoospermia rate of 98%. Plugs have been removed from 86 men and, to date, 51 have made their wives pregnant. In those from which the plugs have been removed for more than 1 year (n- 31), the pregnancy rate is 100%. INTRODUCTION Occlusion of the vas deferens by ligation is now in widespread use as a contraceptive method (1). As normally practiced, it requires a skin incision and some dissection of the vas deferens itself. Although several studies have shown that, under optimal circumstances, surgical vasectomy can be reversed with varying success in terms of pregnancy outcome, the operation of vasovasostomy requires skill and experience in microsurgery (2, 3). For this reason, surgical vasectomy is only offered in Family Planning progammes as an irreversible means of male fertility regulation. It has been recognized for some time that two main factors limit the acceptibility of vas occlusion: one is the necessity for a skin incision, which is unacceptable in some cultures; and the other is the lack of certain reversibility should the family circumstances require this. Amongst many attempts to develop simplified methods to overcome these limitations, research in China, which started in 1970, has led to two major technical improvements: the isolation and ligation of the vas through a puncture (non-scalpel) opening in the skin; and the development for the percutaneous of a technique injection into the vas lumen of sclerotising and other agents through a hypodermic needle (4-7). The present report describes a modification of the method of percutaneous injection which has been used for the introduction into the vas deferens of medical-grade polyurethane elastomer to form a plug ir? z&i&. This method has been in clinical use in China since 1983 and preliminary reports have been given (7, 8). The overall efficacy is high, complications are few and there is accumulating evidence that, in the circumstances examined so far, removal of the plugs leads to recovery of fertility. Submitted for publication July 5, 1989 Accepted for publication January 29, 1990
MAY 1990VOL. 41 NO. 5
463
CONTRACEPTION MATERIAL!3 ANDMIZTHODS A.
Hedicel_ade
oolyurev
Two solutions must be mixed in equal volumes to form the Solution A is formed by the co-polymerization of polytetraplugs. methylene-ether glycol (i~LW.1000) with toluene-2,4-diisocyanate to form a pre-polymer linked by carbamate. Solution B is a chain extender ma& from methylene-bis-ortho-chloroaniline, a catalyst a solvent. Both solutions are liquid at ambient temperature. and They are mixed in equal volumes in a In1 glass syringe just before after which they form a smooth elastomer plug by chain injection, extension. The plug has a Shore hardness of 82-84, 45% elasticity tearing strength of 76-77 kg/cm. B.
The ooeration
for oercutaneous
wection
and a
in man
The present clinical experience is reported for 12,000 men who received the vas occlusion procedure in the period 1983-1987, the majority of whom (87%) were rural farm workers. They were aged 25-50 years, the majority (83.8%) being 25-35 years of age. All had fathered children, the majority (73.2%) having two children. The procedure is an adaptation of that described before (4-6) and is conducted under full aseptic procedures and local procaine anaesthesia. The vas deferens of one side is gripped through the skin by the vas-fixation lifted and an 8-gauge clam9 (Fig.W. (0.8mm diameter) hypodermic needle used to puncture the vas in the direction away from the testis (Fig. 2). This needle is then removed and a 6-gauge (0.6mm) blunt-ended needle inserted into the vas through the channel created by the puncture needle. Fig. 1A
Fig. 16
Atraumatic vas-fixation CkImP
F
T
Circular screw clamp
10 mm
I
!i!i!Y 3mm 0.5 mm
m
t
5mm
91I
ml
7mm
i
Fig. 1. Special instruments.
454
MAY 1990 VOL. 41. NO. 5
CONTRACEPTION Various
tests are used to verify that the needle tip is in the lumen: air injection into a finger-occluded distal section of the vas; the infusion of 5 ml 0.05% congo red (5 ml 0.02% methylene vas). There should be no subcutaneous blue in the contralateral emphysema following the first test or subcutaneous fluid following the second. When both vas deferens have been prepared in this way, 3 ml procaine solution is injected through each needle for its spennicidal action and a specially designed circular screw clamp
Fig. 2. Insertion of the puncture hypodermic
Fig.
3.
Position
MAY 1990 VOL. 41 NO. 5
of
screw
clamp
needle into the vas (6).
during
injection
(P., plug).
455
CONTRACEPTION applied to the scrotal skin to surround (diameter 1 cm; Fig.lB) the portion of the vas enclosing the tips of the injection needles Residual fluid is sucked out of the needle, the needle (FLg. 3). and then a lml glass syringe containing an equal mixture of dried, B is attached. A screw-plunger syringe solution A and solution holder is then applied to the syringe enabling 0.16 - 0.22 ml of elastomer to be injected smoothly through the needle. the viscous injected is adjusted according to the size of the vas The volume deferens and to achieve a bulge in the occluded portion of the injected in turn. The polymerization takes l-3 vas. Each vas is min although 24 hr is needed for complete setting. The subject is asked to urinate at the conclusion of the operation. If dye had been injected previously and the urine is coloured browu, the hjections were bilaterally successful; if the usual colour, both sides were unsuccessful; orange or green colour indicates faihre on one side or the other. Subjects are advised intercourse for 1 month. C.
The oneration
for ulue
to
rest
for 24 hr and
to abstain
from
removal
Permission by the State FamLly Planning Commission of the People's Republic of China was given for the removal of the plugs from 86 men. Their ages ranged from 30 - 35 years and the plugs had been in place for 3 months - 4 years. There are two groups according to length of time since removal of the plugs: group 1 l-2 years since removal; group 2 (n-55), 1-12 months since (n-31), removal. The scrotal prepared and skin is local procaine anaesthesia admincstered exactly as for the procedure for percutaneous injection of clamps (Fig.lA) the vas. Vas-fixation are placed on either side of the vasal segment containing the A short (about 1 cm) incision, not quite through the skin, plug. is made with a hand-held scalpel blade. A pair of sharp haemostat forceps are used to dissect through the skin and around both sides of the vas. The vas-fixation clamps are then transferred to the exposed vas on either side of the occluded section and the vas incised longitudinally (0.5-l cm) over the plug. This is loosened from its attachments to the mucous membrane and then removed with forceps (Fig.4). Usually the incision in the vas does not require a suture although the skin incision does.
Fig.
4. A polyurethane
456
elastomer
plug
after
removal
(scale:
10 mm).
MAY X390VOL. 41. NO. 5
CONTRACEPTION
RESULTS A.
CJQ
56 cases of complications during the first year of There were follow-up amongst the 12,000 men in this report. Of these, 47 were attributable to local infection and 9 to a local haematoma. There were no residual problems in 2.600 men followed-up for 3 years and in 1,000 men followed-up for 5 years. None of the subjects complained of epfdidymal swelling or pain or of any change in sexual function or libido. Of the 12,000 men who received the vas occlusion procedure in the period 1983-1987, the first 500 who accepted to provide semen samples by masturbation were examined after 1 year. Of these, 490 were azoospermic, 5 were severely oligozoospermic with less than 4 million spermatozoa per ml, 2 had sperm concentrations of 4-20 million per ml, and 3 had concentrations exceeding 20 million per ml. The azoospermia rate was therefore 98%. A similar efficacy rate persisted for 100 men who agreed to provide semen after 2 and 3 years of vas occlusion. B.
ei R versib lit
The removal of polyurethane plugs from 86 men has so far resulted in pregnancy of the wives of 51. The results from the two groups established according to the length of time since removal of the plugs, i.e. exceeding 1 year (Group 1, n-31 ) or less than 1 year (Group 2, n-55 ) are shown in the Table. All the wives of the men of Group 1 became pregnant within 1-2 years of reversal of vas occlusion when the semen of most men contained sperm in the normal concentration range. In Group 2, the time since reversal ranged from only 1 month to 1 year. Nevertheless, 37 men produced ejaculates containing sperm at concentrations of 5 (11 men) and 5-20 (26 men) million per ml and 20 wives have become pregnant.
Table Recovery of sperm in the ejaculates of two groups of men from whom the polyurethane plugs have been removed for more than and less than 1 year and the occurrence of pregnancy in their partners
Duration Gou 2
n
occlusion
1 2
31 55
2-4 3/12-l
MAY 1990VOL.
41 NO. 5
(year)
Sperm coDcentration 5-20
l-2 1/12-l
11
6 26
Pregnancy
O-100
no
25 -
31 20
100 36
457
CONTRACEPTION To date, 38 babies have been born, of which 18 are female and 20 male. All babies were normal at birth and no post-natal abnormalities have arisen. The oldest child fathered following vas reversal is now 5 years 8 months. DISCUSSION The percutaneous injection of polyurethane elastomer to form plugs ti g&~ has been accepted by approximately lOQ,OOO men to date and offers a method of vas occlusion which has good efficacy, a low incidence of complications and the possibility of successful reversal. There is a need for skill and practice to achieve percutaneous cannulation of the vas deferens and training schemes have been established for this purpose. The plug formed by the polyurethane elastomer was similar in and elasticity hardness to the vas deferens itself and the subjects did not have any awareness of its presence. The material apparently caused no local or general side effects. When injected in sufficient amount, the polyurethane elastomer formed a plug which maintained its position within the vas and was not moved by peristalsis. Animal toxicity studies suggest that the materials are non toxic (unpublished observations). There is good evidence that the removal of the plugs by the described leads to successful reversibility in simple operation terms of pregnancy outcome. The results available to date suggest that 100% reversibility may occur within 2 years of removal of the is equivalent to the This rate of return to fertility plugs. rate for couples in which both partners have expected pregnancy established proven fertility (9). It should be noted, however, of vas occlusion before removal is less than 4 that the duration years (Table). The success rate of the vasovasostomy operation is reduced when the duration of vasectomy is long (1, 2), althdugh Silber proposes that 'open-ended' vasectomy significantly improves of reversal (to 82%; 3). Future studies will attempt the success the success of reversal following periods of vas to monitor occlusion by plugs of more than 4 years. In conclusion, it is proposed that the non-incision, percutainjection of polyurethane elastomer provides a non-traumatic neous of vas occlusion with several advantages over surgical method It is likely to be more acceptable in some cultures in vasectomy. the world and the possibility of easy reversal could lead to widespread acceptability.
ACKNOWLEDGEMENTS I wish to express my gratitude to Professor Wu Jie-ping who throughout this work. The following served as consultant assisted in various ways: Associate Professors Peng colleagues Shao-bang and Li Guang-jia (chemistry); Professor Tan Pei-jiao
456
MAY 1990 VOL. 41. NO. 5
CONTRACEPTION Long-quan (pathological Associate Professor Yang (toxicology); Yi-he (clinical and Lian Drs. Li Qing-lu examination); assistants). Thanks are also due to Dr. Bianxi Feng for data for his drawings. I am and to Engineer Liu Hou-jun analysis grateful to the State Family Planning CoPPmission and the Shanxi I owe a special Provincial Government for their financial suport. to Dr. G.H.H. Waites. WHO Special Programme of debt of gratitude and Research Training in Human Reproduction Research, Development who revised my draft manuscript for publication.
REFERENCES 1.
Huber DH, Hong S, Ross JA. The international experience with vasectomy. In: Zatuchni GI. Goldsmith A. Spieler JH, Sciarra advances and future prospects. eds. Male contraception: JJ. Philadelphia: Harper and Row, 1986:7-18.
2.
Lee HY. A 20-year experience with vasovasostomy. 136:413-415.
3.
after vasovesostomy for vasectomy Silber SJ. Pregnancy reversal: a study of factors affecting long-term return of fertility in 282 patients followed for 10 years. Human Reprod 1989;4:318-322.
4.
Li The technique Shun-qiang. Chongqing Medicine 1973;3:7-12.
5.
Wu Jie-ping. Contraception by injection of 5% sodium morrhuate into the epididymides. In: The techniques of birth control. Shanghai: Shanghai Publishing House, 1979:242.
6.
Zhu Jin-bo. Ten years clinical study on Li Shun-qiang. for male sterilization. In: Qian percutaneous vas occlusion GMH eds. Advances in Fertility Regulation in the SZ, Waites The People's Medical Publishing House, 1985: Male. Beijing: 75-79.
7.
Chemical vas-occlusion in the People's Republic Xiao Bilian. of China. In: Diczfalusy E, Bygdeman R, eds. Fertility Serono Symposia Publications: Regulation Today and Tomorrow. Raven Press, 1987; 36:265-274.
8.
on reversible blocking Zhao Sheng-cai. Research spermatic duct using injected MPU. Reprod Contracept 12-16.
9.
Lenton EA, Weston GA, Cooke ID. apparently normal couple with a Fertil Steril 1977; 28:913-919.
MAY 199OVOL. 41 NO. 5
of
chemical
vas
J Urol 1986;
occlusion.
of the 1986; 6:
Long-term follow-up of the complaint of infertility.
