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A comparison between Nova T and Copper T 200 Ag in Hungary
Int. J. Gynaecol. Obstet., 1987, 25: 59-63 International
Federation
of Gynaecology
59 & Obstetrics
A COMPARISON BETWEEN NOVA T AND COPPER T 200 Ag IN HUNGARY
ISTVAN
BATARa,
LASZLO
LAMPEa, ISTVAN
RAKOCZIb,
ISTVAN
GATIb and HANNU
ALLONENC
aDepartment of Obstetrics and Gynaecologv, Universiry Medical School, Debrecen, bDeparrment of Obstetrics and Gynaecology, Postgraduate Medical School, Budapest (Hungary) and CHuhtamiiki Oy Pharmaceuricals, Leiras-Medico, Helsinki (Finland) (Received (Accepted
June 6th, 1986) June 20th, 1986)
Abstract Batar I, Lampe L, Rakoczi I, Gati I, Allonen H (Department of Obstetrics and Gynaecology, University Medical School, Debrecen, Department of Obstetrics and Gynaecology, Postgraduate Medical School, Budapest, Hungary and Huhtamiiki Oy Pharmaceuticals, LeirasMedica, Helsinki, Finland). A comparison between Nova T and Copper T 200 Ag in Hungary. Int J Gynaecol Obstet 25: 59-63, 1987 In a comparative use-effectiveness study, 855 Nova T and 883 TCu 200 Ag devices were inserted in a randomised sequence. By the end of the first year the gross rate of unplanned pregnancy was 1.1 per 100 users of Nova T and 2.1 per 100 users of TCu. After 2 years the pregnancy rates for Nova T and TCu were 3.1 and 4.8 per 100 users, respectively. Although there was no statistically significant difference between the rates for the two devices, they suggest a higher contraceptive efficacy for Nova T.
by the experience and talent of the investigators and/or patient selection. A randomised comparative clinical trial is perhaps the best way of avoiding most of the bias in evaluating new devices. Such a study was conducted in Scandinavia with Nova T and Copper T IUDs [4]. Nova T was a new device which was designed to be more flexible than the conventional and highly effective Copper T. Also the effective life-time of Nova T is prolonged by means of a silver core inside the copper wire. The Scandinavian study, with a 5-year followup, showed that the contraceptive efficacy of Nova T was statistically highly significantly better than that of the other device, the pregnancy rate being one third of that with Copper T. Removal rates for medical and personal reasons were comparable for the two IUDs. The purpose of the present study was to compare the contraceptive efficacy and clinical performance of the Nova T and Copper T 200 Ag devices and to determine whether the earlier experience also held good in a Hungarian population. Subjects and methods
Keywords: Intrauterine contraceptive device; TCu 200; Nova T; Contraceptive efficacy; Side effects; Comparative study. Introduction First trials with new types of IUD have often been more promising than subsequent studies. The favourable early results may be explained 0020-7292/8?/303.50 0 1987 International Federation Published and Printed in Ireland
This was a randomised comparative study with two IUDs. Between February 1982 and February 1983, two family planning clinics, in Budapest and Debrecen, Hungary, enrolled 1738 subjects for the study. All consecutive women requesting an IUD, who had no contraindications for a copper-releasing IUD, and who gave their consent were admitted to the IntJ
of Gynaecology
& Obstetrics
Gynaecol Obstet
25
60
Batar et al.
study. The random allocation to contraception with Nova T or Copper T 200 Ag (manufactured by Huhtamaki Oy Leiras, Turku, Finland) was accomplished by preparing a sealed, sequentially numbered envelope containing in randomised order one of the two devices. The insertions were performed during the first 7 days of the menstrual cycle, or at least 6 weeks post partum or post abortum. The subjects were advised to return to the clinic for a check-up 1, 3, 6, 12 and 24 months after insertion, or in the case of problems. Those who failed to return to the clinic at the scheduled time were contacted by letter or telephone. The rates of pregnancy, expulsions and removals for medical or personal reasons were analysed by means of the life-table method suggested by Tietze [ 51. Only one segment of use was analysed for each woman. The statistical significance of differences between groups was evaluated with the logrank chi-square test [ 1 I. A level of 0.05 was used as the criterion for statistical significance. At the time of the analysis, 30 months had elapsed from the last insertion. For the present investigation, 855 Nova Ts and 883 Copper Ts were inserted. The age of the subjects ranged from 18 to 46 years for Nova T acceptors and from 16 to 46 years for Copper T acceptors. The mean age was 30.0 years for both groups. Of all acceptors, 17% were less than 25 years old, and 22% were 35 years old or more. Two per cent were nulliparous, and 10% were of parity 3 or more. There was no statistically significant difference between the age or parity of the users of Nova T and the users of Copper T (see Fig. 1). More than 50% of the women had had either induced or spontaneous abortion. About 65% of those who had earlier been pregnant had had a vaginal delivery with the most recent pregnancy. Respectively, 35% and 36% of the subjects had been using an IUD as the most recent method of contraception. Respectively, 39% and 38% had used a contraceptive pill. None of these parameters suggested any significant difference between the characteristics of the two groups of contraceptors. Int J Gynaecol Obstet
25
60
1
___ __ ,--AlI!
,__ 1
e25 25- Xl- =35 29 34 AGE
3+
PARITY
Fig. 1. Percentage distribution of subjects according to age and parity. Continuous lie, Nova T; broken line, TCu.
Results Of the 855 acceptors of Nova T, 754 completed 12 and 603 completed 24 months follow-up. At 12 months, 6% were lost to follow-up and at 24 months 14%. Of the 883 acceptors of Copper T, 585 completed 24 months follow-up. At 12 months 7% were lost to follow-up, and at 24 months 14.7% (see Table I). Pregnancy
During the first year of observation there were 9 pregnancies among the users of Nova T and 17 pregnancies among the users of Copper T. The first-year gross pregnancy rates were thus 1.1 and 2.1, respectively, per 100 users (Table II), and the figures were the same for the Pearl Index (Table I). The difference was not statistically significant (P = 0.4). During the second year there were another 13 + 18 pregnancies so that the cumulative two-year gross rates were 3.1 and 4.8 (see Table II). The cumulative Pearl Index for the 2-year follow-up was 1.5 for Nova T and 2.4 for Copper T (Table I). The breakdown of the 2-year pregnancy rate by age shows that in different age categories of Nova T users the rate varied from
Comparison between Nova T and TCu Table I.
Number
of subjects
in the study
and the cumulative
number
of events during
2 years.
Nova T
TCu
12 months Insertions Discontinuations Pregnancy Expulsion Bleeding/pain Infection Other medical Planning pregnancy Other personal Released from study Incomplete observations No. completing period Woman-years of use Pearl Index
12 months
131 22 13 44 10 6 28 8 1 120 603 1461
66 17 11 17 2 4 11 4 0 62 755 811
24 months 883
1.1
1.5
3.5 among those under 25 years old to 1.7 in those over 35 years old (see Fig. 2). For Copper T users the age-specific pregnancy rate was as high as 9.3 among women under 25 years, and only 3.3 in women over 35. Although the difference between the two IUDs was not statistically significant, the rate was numerically higher in each age group of Copper T users. The breakdown of the pregnancy rate according to parity did not suggest any clear tendency, except that it was lower for Nova T users in both the lowest and highest parity categories.
Discontinuation
24 months 855
49 9 9 18 4 2 3 4 1 51 754 794
Table 11. Cumulative gross discontinuation
61
168 35 22 44 7 16 34 10 0 130 585 I.471
2.1
2.4
One pregnancy in each group was ectopic. Thus, the rate of ectopic pregnancies in this study, 0.7 per 1000 woman years, is slightly below that reported in clinical trials for copper-releasing IUDs [ 31.
Expulsion In 35 cases, spontaneous expulsion or partial expulsion and removal was the reason for discontinuing the use of IUD during the 2year period. The l-year rates, 1.1 and 1.3, respectively, were roughly comparable for the two devices, and the 2-year rates, 1.7 and 3.0,
rates per hundred acceptors.
Nova T
P
TCu
category 12 months Pregnancy Expulsion Removals Bleeding/pain Infection Other medical Planning pregnan cY Other personal Total terminations
24 months
12 months
24 months
1.1 1.1
3.1 1 .I
2.1 1.3
4.8 3.0
0.3 0.4
2.2 0.5 0.3
6.1 1.4 0.9 4.0 1.1 17.1
2.1 0.3 0.5 1.4 0.5 7.8
6.1 1.0 2.3 4.8 1.5 21.4
0.9 0.9 0.2 0.8 0.9 0.1
0.4 0.5 6.1
Int J Gynaecol Obstet
25
62
Batar et al.
.._ i__ fl h1 c
8
i---l
:‘-7 *
:
:
:
I,
I
:
:
r---q :
:
I
:
r---
6
:
I ;
I
-.
2-
1
35 AGE
2
-
0
3+
~25 25- >35 35
PARITY
1
2
3
PARITY
AGE
Fig. 2. Two-year gross pregnancy rates (per 100 acceptors) according to age and parity. Continuous line, Nova T; broken line, TCu.
Fig. 3. Two-year gross rates (per 100 acceptors) of removals for bleeding/pain according to age and parity. Continuous line, Nova T; broken line, TCu.
respectively, did not differ statistically significantly either (Table II). The age-specific rates did not indicate any clear age-dependent relationship. Also in parity groups the expulsion rate varied in a somewhat non-uniform manner.
year period, 88 women terminated the study for these reasons. At 12 months the removal rates were approximately equal for the two IUDs, i.e. 2.2 and 2.1. During the second year, removals occurred at the same rate, and the 24-month rate was 6.1 for each device (see Tables II and III). No clear connection with age or parity could be observed for either device, removals being equally common in all three age and parity groups (see Fig. 3).
Removals for bleeding and/or pain
As in most IUD studies, the most common reason for discontinuing the use of IUD was pain and/or bleeding problems. Over the 2-
Table III. Cumulative net discontinuation
rates per hundred acceptors.
Discontinuation category
Nova T 12 months
Pregnancy Expulsion Removals Bleeding/pain Infection Other medical Planning pregnancy Other personal Continuation
Int J Gynaecol Obstet 2.5
TCu 24 months
12 months
24 months
1.1 1.1
2.9 1.6
2.0 1.3
4.4 2.8
2.2 0.5 0.2 0.4 0.5 94.0
5.7 1.3 0.8 3.7 1.0 83.0
2.0 0.2 0.5 1.3 0.5 92.2
5.6 0.9 2.1 4.4 1.3 78.6
Comparison between Nova Tand TCu
Other removals The rates for other removals were also very similar for the two IUDs (see Tables II and III). The l-year net rates of removal for other medical reasons, including infections, were 0.7%. Various personal reasons led to removal of the IUD in about l-2% of users. Discussion The removal rates in this study were remarkably low. In many IUD studies, the removal rate for bleeding/pain has been in the range of lo- 15% of users in the first year [ 3 I. The low removal rate may reflect the selection of patients, about 40% of whom were IUD users before entering the study. The low removal rate may also reflect clinical practice, which is also known as the “clinic factor” in clinical trials. The present study compared two IUDs which were relatively similar at least as to general form (t-shaped) and also in having similar copper wire. It is not therefore surprising that there were no statistically significant differences in the discontinuation rates. However, the pregnancy rate with Copper T was twice as high as with Nova T. This difference is not without importance if it is a real difference. The present study was not large enough to show whether the observed difference always holds good or whether it was due to chance. It can be calculated that a comparative study of 3 100 acceptors per device would be necessary in order to provide a 90% chance of detecting, at a 5% significance level, improvement in the pregnancy rate from 2 (the figure for Copper T in this study) to 1 (the figure for Nova T). There are two other published randomised comparisons of Nova T and Copper T. One was performed in Scandinavia, the findings published by Luukkainen [41, and the other
63
in Yugoslavia by Kozuh et al. [ 21. These two studies, as well as the present one, show a similar difference in contraceptive efficacy between Nova T and Copper T. If we pool the data from all these studies, we may say that with this number of subjects the difference between the pregnancy rates (1.0 vs. 2.3) is statistically significant at a level of 5%. The conclusion to be drawn from the present study is that the rate of unwanted pregnancies with Nova T is only half of that with Copper T, but that the clinical performance of Nova T and Copper T is very similar in other respects. This difference in the contraceptive efficacy between Nova T and Copper T may be due to the design of Nova T made in order to increase the flexibility of the device and to improve the chances of keeping the device in the correct fundal position. References Azen SP, Roy S, Pike MC, Casagrande J, Mishell Jr, DR: A new procedure for the statistical evaluation of intrauterine contraception. Am J Obstet Gynecol 128: 329, 1977. Kozuh M, Andolsek L, Allonen H: The comparison of clinical performance of Nova T and Copper T 200 in Yugoslavia. Adv Contracept (in press), 1986. Liskin L: IUDs. An appropriate contraceptive for many women. Popul Rep, Series B, X: 101,1982. Luukkainen T, Allonen H, Nielsen NC, Nygren K-G, Pyorlla T: Five years’ experience of intrauterine contraception with Nova T and Copper T 200. Am J Obstet Gynecol147: 885, 1983. Tietze C, Lewit S: Recommended procedures for the statistical evaluation of intrauterine contraception. Stud Fam Plann 4: 35, 1973.
Address for reprints: Dr. Istvan Batar Department of Obstetrics and Gynaecology University Medical School Box 37,4012 Debrecen Hungary
Int J Gynaecol Obstet
25
Federation
of Gynaecology
59 & Obstetrics
A COMPARISON BETWEEN NOVA T AND COPPER T 200 Ag IN HUNGARY
ISTVAN
BATARa,
LASZLO
LAMPEa, ISTVAN
RAKOCZIb,
ISTVAN
GATIb and HANNU
ALLONENC
aDepartment of Obstetrics and Gynaecologv, Universiry Medical School, Debrecen, bDeparrment of Obstetrics and Gynaecology, Postgraduate Medical School, Budapest (Hungary) and CHuhtamiiki Oy Pharmaceuricals, Leiras-Medico, Helsinki (Finland) (Received (Accepted
June 6th, 1986) June 20th, 1986)
Abstract Batar I, Lampe L, Rakoczi I, Gati I, Allonen H (Department of Obstetrics and Gynaecology, University Medical School, Debrecen, Department of Obstetrics and Gynaecology, Postgraduate Medical School, Budapest, Hungary and Huhtamiiki Oy Pharmaceuticals, LeirasMedica, Helsinki, Finland). A comparison between Nova T and Copper T 200 Ag in Hungary. Int J Gynaecol Obstet 25: 59-63, 1987 In a comparative use-effectiveness study, 855 Nova T and 883 TCu 200 Ag devices were inserted in a randomised sequence. By the end of the first year the gross rate of unplanned pregnancy was 1.1 per 100 users of Nova T and 2.1 per 100 users of TCu. After 2 years the pregnancy rates for Nova T and TCu were 3.1 and 4.8 per 100 users, respectively. Although there was no statistically significant difference between the rates for the two devices, they suggest a higher contraceptive efficacy for Nova T.
by the experience and talent of the investigators and/or patient selection. A randomised comparative clinical trial is perhaps the best way of avoiding most of the bias in evaluating new devices. Such a study was conducted in Scandinavia with Nova T and Copper T IUDs [4]. Nova T was a new device which was designed to be more flexible than the conventional and highly effective Copper T. Also the effective life-time of Nova T is prolonged by means of a silver core inside the copper wire. The Scandinavian study, with a 5-year followup, showed that the contraceptive efficacy of Nova T was statistically highly significantly better than that of the other device, the pregnancy rate being one third of that with Copper T. Removal rates for medical and personal reasons were comparable for the two IUDs. The purpose of the present study was to compare the contraceptive efficacy and clinical performance of the Nova T and Copper T 200 Ag devices and to determine whether the earlier experience also held good in a Hungarian population. Subjects and methods
Keywords: Intrauterine contraceptive device; TCu 200; Nova T; Contraceptive efficacy; Side effects; Comparative study. Introduction First trials with new types of IUD have often been more promising than subsequent studies. The favourable early results may be explained 0020-7292/8?/303.50 0 1987 International Federation Published and Printed in Ireland
This was a randomised comparative study with two IUDs. Between February 1982 and February 1983, two family planning clinics, in Budapest and Debrecen, Hungary, enrolled 1738 subjects for the study. All consecutive women requesting an IUD, who had no contraindications for a copper-releasing IUD, and who gave their consent were admitted to the IntJ
of Gynaecology
& Obstetrics
Gynaecol Obstet
25
60
Batar et al.
study. The random allocation to contraception with Nova T or Copper T 200 Ag (manufactured by Huhtamaki Oy Leiras, Turku, Finland) was accomplished by preparing a sealed, sequentially numbered envelope containing in randomised order one of the two devices. The insertions were performed during the first 7 days of the menstrual cycle, or at least 6 weeks post partum or post abortum. The subjects were advised to return to the clinic for a check-up 1, 3, 6, 12 and 24 months after insertion, or in the case of problems. Those who failed to return to the clinic at the scheduled time were contacted by letter or telephone. The rates of pregnancy, expulsions and removals for medical or personal reasons were analysed by means of the life-table method suggested by Tietze [ 51. Only one segment of use was analysed for each woman. The statistical significance of differences between groups was evaluated with the logrank chi-square test [ 1 I. A level of 0.05 was used as the criterion for statistical significance. At the time of the analysis, 30 months had elapsed from the last insertion. For the present investigation, 855 Nova Ts and 883 Copper Ts were inserted. The age of the subjects ranged from 18 to 46 years for Nova T acceptors and from 16 to 46 years for Copper T acceptors. The mean age was 30.0 years for both groups. Of all acceptors, 17% were less than 25 years old, and 22% were 35 years old or more. Two per cent were nulliparous, and 10% were of parity 3 or more. There was no statistically significant difference between the age or parity of the users of Nova T and the users of Copper T (see Fig. 1). More than 50% of the women had had either induced or spontaneous abortion. About 65% of those who had earlier been pregnant had had a vaginal delivery with the most recent pregnancy. Respectively, 35% and 36% of the subjects had been using an IUD as the most recent method of contraception. Respectively, 39% and 38% had used a contraceptive pill. None of these parameters suggested any significant difference between the characteristics of the two groups of contraceptors. Int J Gynaecol Obstet
25
60
1
___ __ ,--AlI!
,__ 1
e25 25- Xl- =35 29 34 AGE
3+
PARITY
Fig. 1. Percentage distribution of subjects according to age and parity. Continuous lie, Nova T; broken line, TCu.
Results Of the 855 acceptors of Nova T, 754 completed 12 and 603 completed 24 months follow-up. At 12 months, 6% were lost to follow-up and at 24 months 14%. Of the 883 acceptors of Copper T, 585 completed 24 months follow-up. At 12 months 7% were lost to follow-up, and at 24 months 14.7% (see Table I). Pregnancy
During the first year of observation there were 9 pregnancies among the users of Nova T and 17 pregnancies among the users of Copper T. The first-year gross pregnancy rates were thus 1.1 and 2.1, respectively, per 100 users (Table II), and the figures were the same for the Pearl Index (Table I). The difference was not statistically significant (P = 0.4). During the second year there were another 13 + 18 pregnancies so that the cumulative two-year gross rates were 3.1 and 4.8 (see Table II). The cumulative Pearl Index for the 2-year follow-up was 1.5 for Nova T and 2.4 for Copper T (Table I). The breakdown of the 2-year pregnancy rate by age shows that in different age categories of Nova T users the rate varied from
Comparison between Nova T and TCu Table I.
Number
of subjects
in the study
and the cumulative
number
of events during
2 years.
Nova T
TCu
12 months Insertions Discontinuations Pregnancy Expulsion Bleeding/pain Infection Other medical Planning pregnancy Other personal Released from study Incomplete observations No. completing period Woman-years of use Pearl Index
12 months
131 22 13 44 10 6 28 8 1 120 603 1461
66 17 11 17 2 4 11 4 0 62 755 811
24 months 883
1.1
1.5
3.5 among those under 25 years old to 1.7 in those over 35 years old (see Fig. 2). For Copper T users the age-specific pregnancy rate was as high as 9.3 among women under 25 years, and only 3.3 in women over 35. Although the difference between the two IUDs was not statistically significant, the rate was numerically higher in each age group of Copper T users. The breakdown of the pregnancy rate according to parity did not suggest any clear tendency, except that it was lower for Nova T users in both the lowest and highest parity categories.
Discontinuation
24 months 855
49 9 9 18 4 2 3 4 1 51 754 794
Table 11. Cumulative gross discontinuation
61
168 35 22 44 7 16 34 10 0 130 585 I.471
2.1
2.4
One pregnancy in each group was ectopic. Thus, the rate of ectopic pregnancies in this study, 0.7 per 1000 woman years, is slightly below that reported in clinical trials for copper-releasing IUDs [ 31.
Expulsion In 35 cases, spontaneous expulsion or partial expulsion and removal was the reason for discontinuing the use of IUD during the 2year period. The l-year rates, 1.1 and 1.3, respectively, were roughly comparable for the two devices, and the 2-year rates, 1.7 and 3.0,
rates per hundred acceptors.
Nova T
P
TCu
category 12 months Pregnancy Expulsion Removals Bleeding/pain Infection Other medical Planning pregnan cY Other personal Total terminations
24 months
12 months
24 months
1.1 1.1
3.1 1 .I
2.1 1.3
4.8 3.0
0.3 0.4
2.2 0.5 0.3
6.1 1.4 0.9 4.0 1.1 17.1
2.1 0.3 0.5 1.4 0.5 7.8
6.1 1.0 2.3 4.8 1.5 21.4
0.9 0.9 0.2 0.8 0.9 0.1
0.4 0.5 6.1
Int J Gynaecol Obstet
25
62
Batar et al.
.._ i__ fl h1 c
8
i---l
:‘-7 *
:
:
:
I,
I
:
:
r---q :
:
I
:
r---
6
:
I ;
I
-.
2-
1
35 AGE
2
-
0
3+
~25 25- >35 35
PARITY
1
2
3
PARITY
AGE
Fig. 2. Two-year gross pregnancy rates (per 100 acceptors) according to age and parity. Continuous line, Nova T; broken line, TCu.
Fig. 3. Two-year gross rates (per 100 acceptors) of removals for bleeding/pain according to age and parity. Continuous line, Nova T; broken line, TCu.
respectively, did not differ statistically significantly either (Table II). The age-specific rates did not indicate any clear age-dependent relationship. Also in parity groups the expulsion rate varied in a somewhat non-uniform manner.
year period, 88 women terminated the study for these reasons. At 12 months the removal rates were approximately equal for the two IUDs, i.e. 2.2 and 2.1. During the second year, removals occurred at the same rate, and the 24-month rate was 6.1 for each device (see Tables II and III). No clear connection with age or parity could be observed for either device, removals being equally common in all three age and parity groups (see Fig. 3).
Removals for bleeding and/or pain
As in most IUD studies, the most common reason for discontinuing the use of IUD was pain and/or bleeding problems. Over the 2-
Table III. Cumulative net discontinuation
rates per hundred acceptors.
Discontinuation category
Nova T 12 months
Pregnancy Expulsion Removals Bleeding/pain Infection Other medical Planning pregnancy Other personal Continuation
Int J Gynaecol Obstet 2.5
TCu 24 months
12 months
24 months
1.1 1.1
2.9 1.6
2.0 1.3
4.4 2.8
2.2 0.5 0.2 0.4 0.5 94.0
5.7 1.3 0.8 3.7 1.0 83.0
2.0 0.2 0.5 1.3 0.5 92.2
5.6 0.9 2.1 4.4 1.3 78.6
Comparison between Nova Tand TCu
Other removals The rates for other removals were also very similar for the two IUDs (see Tables II and III). The l-year net rates of removal for other medical reasons, including infections, were 0.7%. Various personal reasons led to removal of the IUD in about l-2% of users. Discussion The removal rates in this study were remarkably low. In many IUD studies, the removal rate for bleeding/pain has been in the range of lo- 15% of users in the first year [ 3 I. The low removal rate may reflect the selection of patients, about 40% of whom were IUD users before entering the study. The low removal rate may also reflect clinical practice, which is also known as the “clinic factor” in clinical trials. The present study compared two IUDs which were relatively similar at least as to general form (t-shaped) and also in having similar copper wire. It is not therefore surprising that there were no statistically significant differences in the discontinuation rates. However, the pregnancy rate with Copper T was twice as high as with Nova T. This difference is not without importance if it is a real difference. The present study was not large enough to show whether the observed difference always holds good or whether it was due to chance. It can be calculated that a comparative study of 3 100 acceptors per device would be necessary in order to provide a 90% chance of detecting, at a 5% significance level, improvement in the pregnancy rate from 2 (the figure for Copper T in this study) to 1 (the figure for Nova T). There are two other published randomised comparisons of Nova T and Copper T. One was performed in Scandinavia, the findings published by Luukkainen [41, and the other
63
in Yugoslavia by Kozuh et al. [ 21. These two studies, as well as the present one, show a similar difference in contraceptive efficacy between Nova T and Copper T. If we pool the data from all these studies, we may say that with this number of subjects the difference between the pregnancy rates (1.0 vs. 2.3) is statistically significant at a level of 5%. The conclusion to be drawn from the present study is that the rate of unwanted pregnancies with Nova T is only half of that with Copper T, but that the clinical performance of Nova T and Copper T is very similar in other respects. This difference in the contraceptive efficacy between Nova T and Copper T may be due to the design of Nova T made in order to increase the flexibility of the device and to improve the chances of keeping the device in the correct fundal position. References Azen SP, Roy S, Pike MC, Casagrande J, Mishell Jr, DR: A new procedure for the statistical evaluation of intrauterine contraception. Am J Obstet Gynecol 128: 329, 1977. Kozuh M, Andolsek L, Allonen H: The comparison of clinical performance of Nova T and Copper T 200 in Yugoslavia. Adv Contracept (in press), 1986. Liskin L: IUDs. An appropriate contraceptive for many women. Popul Rep, Series B, X: 101,1982. Luukkainen T, Allonen H, Nielsen NC, Nygren K-G, Pyorlla T: Five years’ experience of intrauterine contraception with Nova T and Copper T 200. Am J Obstet Gynecol147: 885, 1983. Tietze C, Lewit S: Recommended procedures for the statistical evaluation of intrauterine contraception. Stud Fam Plann 4: 35, 1973.
Address for reprints: Dr. Istvan Batar Department of Obstetrics and Gynaecology University Medical School Box 37,4012 Debrecen Hungary
Int J Gynaecol Obstet
25