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Retained second twins in Enugu, Nigeria
International Journal of Gynecology and Obstetrics 81 (2003) 281–285
Article
Retained second twins in Enugu, Nigeria U.U. Aniebue, H.U. Ezegwui, B.C. Ozumba* Department of Obstetrics and Gynecology, University of Nigeria Teaching Hospital (UNTH), Enugu, Nigeria Received 12 November 2002; received in revised form 23 January 2003; accepted 29 January 2003
Abstract Objectives: To review our experience with retained second twin in Enugu, Nigeria, over a 10-year period. Methods: The second twin is retained when a delay of 30 min occurs after the delivery of the first twin. The case notes and records of all twin deliveries at the University of Nigeria Teaching hospital Enugu between January 1991 and December 2000 were retrieved and analyzed. Results: Retained second twin occurred in 1y6 twin deliveries with a resultant perinatal mortality rate of 288.5 per 1000 deliveries which was 1.7 times that of first twin. Malpresentation (54%) and uterine atony (39%) were the principal causes of retained second twins. The place of delivery of the first twin, prolonged birth intervals, oxytocin augmentation of labor and breech extraction affected perinatal outcome. Conclusions: Early recourse to vacuum extraction and cesarean deliveries of retained second twin, effective health education and adequate supervision of primary health care facilities are advocated to reduce this preventable condition. 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. Keywords: Retained second twins; Nigeria
1. Introduction The incidence of multiple pregnancy is known to be very high in Nigeria w1x which, coupled with inadequate antenatal and intrapartum care, results in a high incidence of retained second twin w2,3x. The second twin often has a lower Apgar score and an increased need for resuscitation than the first twin because of intrauterine asphyxia w4x. The incidence of morbidity and perinatal mortality has varied w5–7x and this is possibly related to the quality of intrapartum care received by the moth*Corresponding author. Tel.: q234-42-253496; fax: q23442-252665. E-mail address: [email protected] (B.C. Ozumba).
ers. However, it is known that delay in the delivery of the second twin beyond 30 min of birth of the first is associated with poorer perinatal outcome w8 x . 2. Materials and methods The case notes and records of all twin deliveries at the University of Nigeria Teaching Hospital Enugu between January 1991 and December 2000 were retrieved from the labor ward register and analyzed. The second twin is retained when there is a delay of 30 min after delivery of the first twin. Uterine inertia (atony), mentioned in this paper, is failure of the uterus to contract effectively after the delivery of the first twin. Maternal char-
0020-7292/03/$30.00 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0020-7292(03)00075-4
282
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
Table 1 The distribution of women with deliveries complicated by retained second twins, according to age and parity Age (years)
Nullipara
0–19 20–24 25–29 30–34 )35 Total
Multipara
2 5 2 1 1
3 3 8 2 1
11 (21)
16 (31)
Grand multipara
Total
%
– 4 8 5 5
5 12 18 6 6
10 23 35 21 12
25 (48)
52
100
The mean maternal age was 27.7"3 years. Table 2 Obstetric complications associated with 52 retained second twins Factors
Number
Percentage
Tight cord around the neck Intact amniotic sac Compound presentation Hand prolapse Transverse lie Breech presentation Uterine inertiaa (atony)
1 3 3 4 7 14 20
2 6 6 8 14 27 39
a Uterine inertia is the failure of the uterus to contract effectively after the delivery of the first twin.
acteristics of age, parity and place of delivery of first twin were noted. Mode of delivery of first twin and second twin as well as perinatal outcome were also recorded. Analysis of results were done using the EPI INFO version 5.0 (Center for Disease Control, Atlanta, Georgia, 1991). The x2-test was done to determine statistical significance at the 95% confidence level.
3. Results There were 16 324 deliveries during the 10-year period of review. Three hundred and nineteen were twins out of which 52 were retained giving an incidence of retained second twins of 1y6 twins or 0.32% of all deliveries. A twinning rate of 1y51 births was noted in this study. Eighteen triplet births and two quadruplets births were recorded during the same period. Table 1 shows the characteristics of women delivered of a retained second twin. The maternal ages ranged from 19 to 40 years and the parity from 0 to 7. The mean maternal age was 27.7"3 years. Table 2 shows the obstetric complications associated with retained second twins. Compound presentation, transverse lie with or without hand prolapse and breech presentation (malpresentation) accounted for 54% of all cases. The intact amniotic sac and other factors related to uterine atony were seen in 6% and 39% of cases, respectively.
Table 3 The contribution of the place of delivery of the first twin in the prevalence of 52 retained second twins and perinatal mortality in the affected twins Place
Number of retained twins (%)
Perinatal mortality First twin (%)
Second twin (%)
UNTHyPRIVyGen. hosp.y maternity homes Traditional birth attendants Unstated
6 (12)
3 (6)
3 (6)
44 (85)
6 (12)
11 (21)
Total
52 (100)
2 (4)
– 9 (17)
Retained second twins had a higher but insignificant mortality than the first twin (Ps0.16).
1 (2) 15 (29)
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
283
Table 4 The relationship of birth interval between the twins and perinatal mortality in retained second twins Birth interval between firstysecond twins (Min)
Number of retained second twins
Perinatal mortality
30–59 60–199 G120 Total
16 11 25 52
3 2 10 15
(6%) (4%) (19%) (29%)
Deliveries conducted more than 120 min after the birth of the first twin had significantly higher mortality than those delivered between 30 and 199 min (P-0.05; 0.07–1.21 95% confidence interval).
Table 3 shows the relationship between the place of delivery of the first twin and perinatal mortality. Although 48% of the women were booked into the UNTH, only 6% actually delivered their first twin in the hospital. Admission of cases referred from maternity homes and traditional birth attendants accounted for 95% of cases. Retained second twin had a perinatal mortality rate of 228.5y1000 deliveries which was 1.7 times higher than 173y1000 deliveries recorded for the first twin (Ps0.16). Table 4 and Fig. 1 show the effect of birth interval on mortality and morbidity patterns in retained twins. The birth interval between the first and retained twins, ranged from 31 min to more than 48 h. The percentage mortality was 1.9 times higher in babies delivered after 120 min of retention than in those delivered earlier (P-0.05, 95% confidence interval 0.07–1.21). Fig. 1 illustrates the Apgar score at 5 min in retained twins with increasing birth intervals. The effect of the method of delivery of the retained twin on perinatal mortality is shown in Table 5. The indications for cesarean section in retained twins were fetal distress (six cases), transverse lie (six cases), compound presentation (two cases), previous cesarean section (two cases) and a case of failed vacuum extraction. One fetus was delivered by decapitation due to transverse lie and fetal demise. There were no maternal deaths. Postpartum hemorrhage occurred in 17 (33%) cases. Three women (6%) sustained lower genital tract lacerations and postpartum hypertension was seen in two women (4%).
The patient delivered by destructive surgery sustained rupture of the uterus, which was repaired at laparotomy. The rest of the maternal complications (6%) included a case of puerperal sepsis, wound dehiscence and Asherman’s syndrome. 4. Discussion Retained second twins has continued to feature in obstetric practice in developing countries, including Nigeria, as a result of inadequate and poor utilization of modern obstetric services w2,9x. The incidence of retention of 1 in 6 twin births which was recorded in this review is much higher than 1 in 30 twins reported a decade and half ago from this center w3x. It was comparable with a rate of 1 in 7 twin births reported from Ibadan, Nigeria in 1972 w2x. This deterioration may be related to recent economic and social reversals prevalent in the country which have adversely affected the quality of health services provided. Malpresentation 54% and uterine atony 39% were associated with retained twins in the majority of cases, similar to reports in other studies w2,3,9x. Poor obstetric care could readily be held responsible for a good number of cases since 85% of the deliveries which resulted in the retained second twin were supervised in peripheral centers such as maternity homes and maternity services run by traditional birth attendants. This is not surprising since management of twin pregnancy requires specialist care, which invariably does not exist in the peripheral centers. The perinatal mortality rate 286.5y1000 deliveries recorded in this review is particularly high and is 1.7 times the rate of 173y1000 deliveries
284
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
Fig. 1. The relationship between the birth interval and Apgar score at 5 min in retained twins.
Table 5 The relationship between the methods of delivery of the retained twin and perinatal outcome Method of delivery
Number
Live birth
Perinatal mortality
1. Spontaneous vertex delivery a. Amniotomy only b. Syntocinon augmentation 2. Assisted breech 3. Vacuum extraction 4. Breech extraction 5. Cesarean section 6. Destructive surgery
3 15 7 5 4 17 1
3 9 6 5 2 12 –
– 6 1 – 2 5 1
Total
52
37
15 (29%)
Syntocinon augmentation of labor and breech extraction resulted in the highest rates of perinatal mortality.
(40%) (14%) (50%) (29%) (100%)
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
which was recorded for the first twin. Retained second twin referred from peripheral centers not only contributed the bulk of the cases but accounted for 80% of the perinatal mortality. It is known that repeated attempts at manipulative delivery by inexperienced or inappropriately trained accoucheur and long birth interval with its associated progressive hypoxia are more common in such cases. Although retained twin were uncommon in UNTH and the secondary health care facilities, the odds of perinatal mortality in affected deliveries in these facilities when compared with cases from primary health care facilities was 4.18 (Ps0.019). Late invitation of a more experienced obstetrician and logistics difficulties were responsible for late interventions in the three cases treated at UNTH. Early ‘inter- and intra’-hospital referrals are essential to minimize complications in twin deliveries. The use of intravenous syntocinon in the augmentation of labor in retained twins has continued to elicit lively discussion w2,10x. Its use resulted in a perinatal death rate of 40% and followed breech extraction as the most commonly associated factor predisposing to the high perinatal mortality. The absence of facilities for continuous fetal heart monitoring in Enugu, probably heightened the risk associated with augmentation of labor using syntocinon. The fewest perinatal deaths were recorded when labor was merely expedited by amniotomy or the fetus delivered immediately by vacuum extraction. Abdominal delivery by cesarean section usually involves less manipulation and was associated with a perinatal mortality rate of 29%. Breech extraction is reserved for cases where the unborn second twin is in grave danger such as cord prolapse and thus may have led to the particularly high perinatal mortality rate associated with it. The Apgar score pattern at 5 min shown in Fig. 1 was poor with prolonged birth interval. Increasing birth interval did not, however, significantly affect the prevalence of low Apgar scores at 5 min and four babies surprisingly had Apgar scores of 7 or more after more than 700 min (11.6 h) of retention. This is
285
similar to recent reports on delayed intervals delivery in multiple pregnancies w11,12xfrom developed countries. These babies, however, represent only 8% of the retained twins and the percentage perinatal mortality in the study was 1.9 times higher in babies delivered after 120 min retention than in those delivered earlier (P-0.05). Maternal morbidity was high and was mostly associated with the effects of prolonged labor and cesarean section. In conclusion, early recourse to vacuum extraction and cesarean deliveries of retained second twin, effective health education and adequate supervision of primary health care facilities are advocated to reduce this preventable condition. References w1x John CT, Oruambo RS. Multiple births in Port Harcourt: analysis of associated biological variables and problems in classification of growth retarded twins. Trop J Obstet Gynaecol 1999;9:9 –12. w2x Adeleye JA. Retained second twin in Ibadan: its fate and management. Am J Obstet Gynecol 1972;114:2044 –2047. w3x Iloabachie GC. The place of ventouse in the management of retained second twin. Orient J Med 1991;3:160 – 162. w4x Hundal Wre MH. Second twin. Am J Obstet Gynecol 1971;110:865 –869. w5x Cetrulo CL, Ingardia CJ, Sabara AJ. Management of multiple gestation. Clin Obstet Gynecol 1980;23:535 – 548. w6x Buekens P, Wilcox A. Why do small twins have a lower mortality rate than smaller singletons? Am J Obstet Gynecol 1993;168:937 –941. w7x Prins RP. The second born twin: can we improve outcome. Am J Obstet Gynecol 1994;170:1649 –1657. w8x Kenny JP, Corbert AJ, Adams JM, et al. Hyaline membrane disease and acidosis at birth in twins. Obstet Gynecol 1977;50:710 –712. w9x Adinma JI, Agbai AO. The second twin retained and unretained. Trop Doc 1995;25:132 –133. w10x Perry HB. The second twin (discussion). Am J Obstet Gynecol 1971;110:869. w11x Dornon L. A living retained second twin 4 days after. Trop Doc 1992;22:34 –35. w12x Porreco RP, Sabin EP, Heyborne KP, Linsay LG. Delayed interval delivery in multifetal pregnancy. Am J Obstet Gynecol 1998;178:20 –30.
Article
Retained second twins in Enugu, Nigeria U.U. Aniebue, H.U. Ezegwui, B.C. Ozumba* Department of Obstetrics and Gynecology, University of Nigeria Teaching Hospital (UNTH), Enugu, Nigeria Received 12 November 2002; received in revised form 23 January 2003; accepted 29 January 2003
Abstract Objectives: To review our experience with retained second twin in Enugu, Nigeria, over a 10-year period. Methods: The second twin is retained when a delay of 30 min occurs after the delivery of the first twin. The case notes and records of all twin deliveries at the University of Nigeria Teaching hospital Enugu between January 1991 and December 2000 were retrieved and analyzed. Results: Retained second twin occurred in 1y6 twin deliveries with a resultant perinatal mortality rate of 288.5 per 1000 deliveries which was 1.7 times that of first twin. Malpresentation (54%) and uterine atony (39%) were the principal causes of retained second twins. The place of delivery of the first twin, prolonged birth intervals, oxytocin augmentation of labor and breech extraction affected perinatal outcome. Conclusions: Early recourse to vacuum extraction and cesarean deliveries of retained second twin, effective health education and adequate supervision of primary health care facilities are advocated to reduce this preventable condition. 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. Keywords: Retained second twins; Nigeria
1. Introduction The incidence of multiple pregnancy is known to be very high in Nigeria w1x which, coupled with inadequate antenatal and intrapartum care, results in a high incidence of retained second twin w2,3x. The second twin often has a lower Apgar score and an increased need for resuscitation than the first twin because of intrauterine asphyxia w4x. The incidence of morbidity and perinatal mortality has varied w5–7x and this is possibly related to the quality of intrapartum care received by the moth*Corresponding author. Tel.: q234-42-253496; fax: q23442-252665. E-mail address: [email protected] (B.C. Ozumba).
ers. However, it is known that delay in the delivery of the second twin beyond 30 min of birth of the first is associated with poorer perinatal outcome w8 x . 2. Materials and methods The case notes and records of all twin deliveries at the University of Nigeria Teaching Hospital Enugu between January 1991 and December 2000 were retrieved from the labor ward register and analyzed. The second twin is retained when there is a delay of 30 min after delivery of the first twin. Uterine inertia (atony), mentioned in this paper, is failure of the uterus to contract effectively after the delivery of the first twin. Maternal char-
0020-7292/03/$30.00 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0020-7292(03)00075-4
282
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
Table 1 The distribution of women with deliveries complicated by retained second twins, according to age and parity Age (years)
Nullipara
0–19 20–24 25–29 30–34 )35 Total
Multipara
2 5 2 1 1
3 3 8 2 1
11 (21)
16 (31)
Grand multipara
Total
%
– 4 8 5 5
5 12 18 6 6
10 23 35 21 12
25 (48)
52
100
The mean maternal age was 27.7"3 years. Table 2 Obstetric complications associated with 52 retained second twins Factors
Number
Percentage
Tight cord around the neck Intact amniotic sac Compound presentation Hand prolapse Transverse lie Breech presentation Uterine inertiaa (atony)
1 3 3 4 7 14 20
2 6 6 8 14 27 39
a Uterine inertia is the failure of the uterus to contract effectively after the delivery of the first twin.
acteristics of age, parity and place of delivery of first twin were noted. Mode of delivery of first twin and second twin as well as perinatal outcome were also recorded. Analysis of results were done using the EPI INFO version 5.0 (Center for Disease Control, Atlanta, Georgia, 1991). The x2-test was done to determine statistical significance at the 95% confidence level.
3. Results There were 16 324 deliveries during the 10-year period of review. Three hundred and nineteen were twins out of which 52 were retained giving an incidence of retained second twins of 1y6 twins or 0.32% of all deliveries. A twinning rate of 1y51 births was noted in this study. Eighteen triplet births and two quadruplets births were recorded during the same period. Table 1 shows the characteristics of women delivered of a retained second twin. The maternal ages ranged from 19 to 40 years and the parity from 0 to 7. The mean maternal age was 27.7"3 years. Table 2 shows the obstetric complications associated with retained second twins. Compound presentation, transverse lie with or without hand prolapse and breech presentation (malpresentation) accounted for 54% of all cases. The intact amniotic sac and other factors related to uterine atony were seen in 6% and 39% of cases, respectively.
Table 3 The contribution of the place of delivery of the first twin in the prevalence of 52 retained second twins and perinatal mortality in the affected twins Place
Number of retained twins (%)
Perinatal mortality First twin (%)
Second twin (%)
UNTHyPRIVyGen. hosp.y maternity homes Traditional birth attendants Unstated
6 (12)
3 (6)
3 (6)
44 (85)
6 (12)
11 (21)
Total
52 (100)
2 (4)
– 9 (17)
Retained second twins had a higher but insignificant mortality than the first twin (Ps0.16).
1 (2) 15 (29)
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
283
Table 4 The relationship of birth interval between the twins and perinatal mortality in retained second twins Birth interval between firstysecond twins (Min)
Number of retained second twins
Perinatal mortality
30–59 60–199 G120 Total
16 11 25 52
3 2 10 15
(6%) (4%) (19%) (29%)
Deliveries conducted more than 120 min after the birth of the first twin had significantly higher mortality than those delivered between 30 and 199 min (P-0.05; 0.07–1.21 95% confidence interval).
Table 3 shows the relationship between the place of delivery of the first twin and perinatal mortality. Although 48% of the women were booked into the UNTH, only 6% actually delivered their first twin in the hospital. Admission of cases referred from maternity homes and traditional birth attendants accounted for 95% of cases. Retained second twin had a perinatal mortality rate of 228.5y1000 deliveries which was 1.7 times higher than 173y1000 deliveries recorded for the first twin (Ps0.16). Table 4 and Fig. 1 show the effect of birth interval on mortality and morbidity patterns in retained twins. The birth interval between the first and retained twins, ranged from 31 min to more than 48 h. The percentage mortality was 1.9 times higher in babies delivered after 120 min of retention than in those delivered earlier (P-0.05, 95% confidence interval 0.07–1.21). Fig. 1 illustrates the Apgar score at 5 min in retained twins with increasing birth intervals. The effect of the method of delivery of the retained twin on perinatal mortality is shown in Table 5. The indications for cesarean section in retained twins were fetal distress (six cases), transverse lie (six cases), compound presentation (two cases), previous cesarean section (two cases) and a case of failed vacuum extraction. One fetus was delivered by decapitation due to transverse lie and fetal demise. There were no maternal deaths. Postpartum hemorrhage occurred in 17 (33%) cases. Three women (6%) sustained lower genital tract lacerations and postpartum hypertension was seen in two women (4%).
The patient delivered by destructive surgery sustained rupture of the uterus, which was repaired at laparotomy. The rest of the maternal complications (6%) included a case of puerperal sepsis, wound dehiscence and Asherman’s syndrome. 4. Discussion Retained second twins has continued to feature in obstetric practice in developing countries, including Nigeria, as a result of inadequate and poor utilization of modern obstetric services w2,9x. The incidence of retention of 1 in 6 twin births which was recorded in this review is much higher than 1 in 30 twins reported a decade and half ago from this center w3x. It was comparable with a rate of 1 in 7 twin births reported from Ibadan, Nigeria in 1972 w2x. This deterioration may be related to recent economic and social reversals prevalent in the country which have adversely affected the quality of health services provided. Malpresentation 54% and uterine atony 39% were associated with retained twins in the majority of cases, similar to reports in other studies w2,3,9x. Poor obstetric care could readily be held responsible for a good number of cases since 85% of the deliveries which resulted in the retained second twin were supervised in peripheral centers such as maternity homes and maternity services run by traditional birth attendants. This is not surprising since management of twin pregnancy requires specialist care, which invariably does not exist in the peripheral centers. The perinatal mortality rate 286.5y1000 deliveries recorded in this review is particularly high and is 1.7 times the rate of 173y1000 deliveries
284
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
Fig. 1. The relationship between the birth interval and Apgar score at 5 min in retained twins.
Table 5 The relationship between the methods of delivery of the retained twin and perinatal outcome Method of delivery
Number
Live birth
Perinatal mortality
1. Spontaneous vertex delivery a. Amniotomy only b. Syntocinon augmentation 2. Assisted breech 3. Vacuum extraction 4. Breech extraction 5. Cesarean section 6. Destructive surgery
3 15 7 5 4 17 1
3 9 6 5 2 12 –
– 6 1 – 2 5 1
Total
52
37
15 (29%)
Syntocinon augmentation of labor and breech extraction resulted in the highest rates of perinatal mortality.
(40%) (14%) (50%) (29%) (100%)
U.U. Aniebue et al. / International Journal of Gynecology and Obstetrics 81 (2003) 281–285
which was recorded for the first twin. Retained second twin referred from peripheral centers not only contributed the bulk of the cases but accounted for 80% of the perinatal mortality. It is known that repeated attempts at manipulative delivery by inexperienced or inappropriately trained accoucheur and long birth interval with its associated progressive hypoxia are more common in such cases. Although retained twin were uncommon in UNTH and the secondary health care facilities, the odds of perinatal mortality in affected deliveries in these facilities when compared with cases from primary health care facilities was 4.18 (Ps0.019). Late invitation of a more experienced obstetrician and logistics difficulties were responsible for late interventions in the three cases treated at UNTH. Early ‘inter- and intra’-hospital referrals are essential to minimize complications in twin deliveries. The use of intravenous syntocinon in the augmentation of labor in retained twins has continued to elicit lively discussion w2,10x. Its use resulted in a perinatal death rate of 40% and followed breech extraction as the most commonly associated factor predisposing to the high perinatal mortality. The absence of facilities for continuous fetal heart monitoring in Enugu, probably heightened the risk associated with augmentation of labor using syntocinon. The fewest perinatal deaths were recorded when labor was merely expedited by amniotomy or the fetus delivered immediately by vacuum extraction. Abdominal delivery by cesarean section usually involves less manipulation and was associated with a perinatal mortality rate of 29%. Breech extraction is reserved for cases where the unborn second twin is in grave danger such as cord prolapse and thus may have led to the particularly high perinatal mortality rate associated with it. The Apgar score pattern at 5 min shown in Fig. 1 was poor with prolonged birth interval. Increasing birth interval did not, however, significantly affect the prevalence of low Apgar scores at 5 min and four babies surprisingly had Apgar scores of 7 or more after more than 700 min (11.6 h) of retention. This is
285
similar to recent reports on delayed intervals delivery in multiple pregnancies w11,12xfrom developed countries. These babies, however, represent only 8% of the retained twins and the percentage perinatal mortality in the study was 1.9 times higher in babies delivered after 120 min retention than in those delivered earlier (P-0.05). Maternal morbidity was high and was mostly associated with the effects of prolonged labor and cesarean section. In conclusion, early recourse to vacuum extraction and cesarean deliveries of retained second twin, effective health education and adequate supervision of primary health care facilities are advocated to reduce this preventable condition. References w1x John CT, Oruambo RS. Multiple births in Port Harcourt: analysis of associated biological variables and problems in classification of growth retarded twins. Trop J Obstet Gynaecol 1999;9:9 –12. w2x Adeleye JA. Retained second twin in Ibadan: its fate and management. Am J Obstet Gynecol 1972;114:2044 –2047. w3x Iloabachie GC. The place of ventouse in the management of retained second twin. Orient J Med 1991;3:160 – 162. w4x Hundal Wre MH. Second twin. Am J Obstet Gynecol 1971;110:865 –869. w5x Cetrulo CL, Ingardia CJ, Sabara AJ. Management of multiple gestation. Clin Obstet Gynecol 1980;23:535 – 548. w6x Buekens P, Wilcox A. Why do small twins have a lower mortality rate than smaller singletons? Am J Obstet Gynecol 1993;168:937 –941. w7x Prins RP. The second born twin: can we improve outcome. Am J Obstet Gynecol 1994;170:1649 –1657. w8x Kenny JP, Corbert AJ, Adams JM, et al. Hyaline membrane disease and acidosis at birth in twins. Obstet Gynecol 1977;50:710 –712. w9x Adinma JI, Agbai AO. The second twin retained and unretained. Trop Doc 1995;25:132 –133. w10x Perry HB. The second twin (discussion). Am J Obstet Gynecol 1971;110:869. w11x Dornon L. A living retained second twin 4 days after. Trop Doc 1992;22:34 –35. w12x Porreco RP, Sabin EP, Heyborne KP, Linsay LG. Delayed interval delivery in multifetal pregnancy. Am J Obstet Gynecol 1998;178:20 –30.