Perinatal factors and neonatal morbidity in twin pregnancy

Perinatal factors and neonatal morbidity in twin pregnancy SZE PAUL

KUEN

HO,

Y.

Los Angeles,

K.

M.B.,

WU,

M.B.,

B.S. B.S.

California

There were 177 pairs of twins reviewed. The incidence of twin pregnancy was 1:112.2 deliveries in a population consisting of 76.8 per cent Mexican-Americans. The incidence of breech, cesarean section, and assisted deliveries was higher in twins than singleton deliveries, and the incidence was higher in twin 2 than twin 1. Mortality rates, fetal and neonatal, were lower than those previously reported. Neonatal findings and complications include low Apgar scores, small-for-dates infants, hyaline membrane disease, hypoglycemia, hypocalcemia, hyperbilirubinemia, and congenital malformation. The increased incidence of deaths and morbidity in twin pregnancy, as compared to singleton pregnancy, was attributed to prematurity, and to complications and diseases pertaining to prematurity, rather than to twinning per se.

Method The present study involves all twins delivered at the Women’s Hospital of the Los Angeles CountyUSC Medical Center during the 2 year period from January 1, 1972, to December 31, 1973. The majority of the hospital population belonged to the lower social and economic group. Of the 19,855 deliveries in this 2 year period, 75 per cent were Mexican-American and 15 per cent were black. During the 24 month study period, 6,157 mothers of 19,855 deliveries were monitored in the fetal intensive-care unit, representing 31 per cent of all deliveries. Almost all high-risk pregnancies delivered in the medical center were monitored. Since twin pregnancies were considered to be high-risk pregnancies, they were monitored during labor whenever possible. An internal monitor was used in the first twin if membranes were ruptured while the second twin was monitored by external monitors. The fetal-placental weight ratio was calculated by using the combined weight of both babies and the weight of both placentas,.fused or separated. All newborn babies were admitted into the newborn nurseries, which were divided into two main sections : the normal term baby nursery and the special-care nursery. The latter was subdivided into the intensive-care unit and the intermediate-care

RECENT ADVANCES in the management of high-risk pregnancy have led to improvement in the care of both mother and offspring. The impact of these advances is reflected in the improvement in rates of mortality and morbidity in neonates.’ Based on perinatal mortality rates, multiple pregnancies are certainly regarded as high-risk pregnancies. Previous reports on twin pregnancies involved patients studied in an era when fetal monitoring and neonatal intensive care were either nonexistent or in their infancy.‘, ’ In view of the above considerations, the study of twin pregnancies in an institution where both fetal monitoring and neonatal intensive care are available may provide additional insight, especially as it relates to neonatal deaths and morbidity. From the Departments of Pediatrics and and Gynecology, University of Southern School of Medicine, and Los Angeles County-USC Medical Center. Supported in part by a grant from Philips-Duphar, The Netherlands. Received Revised Accepted

for publication February February

December

Obstetrics California

B. V. 10, 1974.

3, 1975. 3, 1975.

Reprint requests: Dr. P. Y. K. Wu, Women’s Hospital, Los Angeles County-USC Medical Center, 1240 Mission Rd., Los Angeles, California 90033. 979

980

Ho and Wu

Table

Am.

I. Sex ratio of twins* Sex Like-sex Unlike-sex Total

1 No. of pairs

*Female-male

Table

ratio

II. Twins:

(

Males

/

116 58

58

177

174

180

1.034.1 (p =

=

fetal-placental

122

> 0.45).

ratio of 78 cases

Fetal-placental

Gestation

No.

(wk.)

Females

119 58

Mean

of cases

weight 1

ratio

I S.D.

28-32

5

3.66

0.96

33-35 36-38

12 28 33

4.56 5.23 5.60

0.82 1.18 0.82

39-41

Table III. Percentage distribution of the twin babies into the various Apgar score groups I min. O-3

Twin (167)” Twin (1671

1 2

6.0 (10) 16.1

Apgar /

Score (70)

4-6

13.8 (23) 22.2 (37)

1 7-10 80.2 (134) 61.7 (103)

5 min. 1

Apgar

score

(76)

0.3

1 4-6

( 7-10

1.8 (3) 4.8

4.2 (7) 8.4 (14)

94.0 (157) 86.8 (145)

(271 (8) *Numbers in parentheses indicate the number of babies.

nursery. The delivered in the normal was 3 days, mediate-care mission into

majority of the babies (91 per cent) the medical center were admitted into baby nursery, where their average stay 7 per cent were cared for in the internursery, and 2 per cent required adthe intensive-care unit.

Results

Demographic data. In this 2 year period 177 pairs of twins were born among 19,855 deliveries-a total incidence of twinning of 8.9 per 1,000 deliveries, or 1 : 112.2 deliveries. Among these 177 mothers 76.8 per cent were Mexican-American, 11.9 per cent were black, 10.8 per cent were non-Mexican white, and one mother was a Filipino. The sex distribution of these 177 sets of twins is shown in Table I. NO significant differences were found in the incidence of twins between male and female. Obstetric data. The majority of mothers in our hospital were young mothers; 64 per cent of the twins were born of mothers 20 to 29 years old and 52 per cent to those of a parity of 1 or 2. The incidence of cephalic presentation for all the twins, whether delivered vaginally or by cesarean

August J. Obstrt.

15, 1975 Cynecol.

section, in the present series was 69 per cent; for the first twin it was 79 per cent and for the second twin 59 per cent. Among the 354 twin babies ( 177 pairs ) , 283 were delivered vaginally; 77 per cent of them were delivered by vertex, while 23 per cent were by breech. When comparing between the first and second twins, 17 per cent of the first twins were delivered by breech, as compared to -I-l per rent for the second twins. The incidence of vacuum extraction for the twin babies was 2.7 per cent and the incidence of midforceps deliveries was 8.8 per cent. Out of 177 pairs of twins, 34 were delivered by cesarean section either electively or as an emergency measure. Three second-twin babies were delivered by cesarean section after the first twin was delivered vaginally. One of these was a transverse lie, the second one was a footling breech presentation with cephalopelvic disproportion, and the third one showed evidence of fetal distress by fetal heart rate pattern after the precipitous delivery of the first twin. Altogether, 71 out of 35-l twin babies were delivered by cesarean section-~~-a total incidence of 20 per cent. The time interval between twin births was a lognormal pattern: 64 per cent of second twins were delivered within 15 minutes after the first twin was born, 86 per cent within 30 minutes, and 2.3 per cent in more than 1 hour. Intrapartum fetal monitoring. Thirty-six per cent of twin deliveries were monitored during the period of the study. Among the 177 pairs of twins studied, there were 53 pairs in whom both twins were monitored. In 12 instances only the first twin was monitored and in 10 instances the second twin was monitored by an internal monitor after delivery of the first twin. Fetal-placental weight ratio. Placental weight was recorded in 78 deliveries. The results are tabulated according to stages of gestation in Table II. Apgar score. The 1 minute and 5 minute Apgar scores are analyzed in Table III. Second twins had a higher incidence of Apgar scores below 7 both at 1 minute (p < 0.001) and at 5 minutes (p < 0.01). Birth weight and gestational age. Among the 354 twin babies, 55 per cent were low-birth-weight (L.B.W.) infants, with birth weights less than 2,500 grams. The babies are classified into weight groups in the first two columns of Table IV. Only 64 per cent of the babies were delivered at term, 33 per cent were preterm (< 37 weeks), and

Volume Number

122 8

Twin

Table IV. Twin

mortality

Birth

weight (Cm.) _< 500 501-1,000 l,OOl-1,500 1,501-2,000 ?,OOl-2,500 > 2,500

all

Table V. Twin

3 21 21 43 108 158

0 16 19 41 105 158

0 57.1 33.3 4.6 1.9 0

339

incidence

deaths with 1

Gestation (wk.) 28 28-30 31-33 34-36 37-41 42

N.N.D. %

over-all

of total

reference

1

rate

+ fetal

*Numbers

4.2 death)

Total

No.

Twins

3 5 2 2 3

100 80.9 42.8 9.2 4.7 0

15

N.N.D.*

No. of total births

No. of live births

70

14 10 32 60 228 10

9 9 28 58 224 10

88.9 77.8 10.7 5.1 0.9 0

= number deaths per 27: 47,

of deaths 100 total

in parentheses

(92)

)

Over

in the same

all*

100 71.7 37.2 10.4 1.0 0.17 2.4 2 year

period.

No.

%

8 7 3 3 2

35.7 10 12.5 1.7 1.8 0

deaths+ No. 5 1 4 1 4

per 100 live births within deliveries (both live birth

deaths

(To)

Present series

Hendrick’s seriesl:

92.9 80 21.9 6.7 2.6 0

95.2 77.8 17.2 7.2 2.2 12.5

the same gestational age group. and fetal death) within the same

gesta-

1966.

deaths of twins

born

the number

as compared

Deaths

of

19,855 354 177 177 indicate

Fetal

1

distribution of fetal and neonatal for the same period

all twins 1 2

death

10.7

of the hospital

Total

No. babies Over Total Twin Twin

/

to gestation

Table VI. Percentage Hospital

deaths

% 100 23.8 9.5 4.6 2.8 0

z

(N.N.D

Fetal

1

*N.N.D. = neonatal death (%) tFeta1 deaths = number of fetal tional age group. $Hendricks, D.: Obstet. Gynecol.

Women’s

No. 12 7 2 2

6.5

death

981

weight

No. of live births

354 =

to birth

No. of total births

Total *Over

with reference

pregnancy

Fetal 1.36 4.24 3.39 5.08

(273)” (15)

I

figure

in

(%)

Neonatal 1.07 6.5 4.52 8.47

to the over-all

Total

I

(211) (23)

(8) (15)

2.43 10.74 7.91 13.55

(484) (38) (14) (24)

of cases.

3 per cent postterm (2 42 weeks). They are analyzed according to gestational ages in Table V. Among the first twins, 20 per cent were considered to have intrauterine growth retardation (I.U.G.R.) and among the second twins 27 per cent had I.U.G.R., as they were below the tenth percentile when plotted on the Lubchenco intrauterine growth curve. Altogether, 23.5 per cent of the twin babies were small for gestational age. Deaths. Among the 354 twin babies there were 15 fetal and 23 neonatal deaths. Table VI shows the percentage distribution of perinatal deaths of twins compared with the over-all incidence in our hospital for the same period. Of the 339 live-born twin babies, 23 died in the neonatal period-eight

first twins (4.5 per cent) and 15 second twins (8.5 per cent)-a total neonatal death rate of 6.5 per cent. The incidence and percentage of fetal and neonatal deaths are analyzed in detail in Table IV according to birth weight groups. The mortality rate for L.B.W. twin babies was 13 per cent. There were no fetal or neonatal deaths in the twin babies weighing over 2,500 grams at birth and 83 per cent of the neonatal deaths were in the group of babies whose birth weight was below 1,500 grams. The incidence and percentage of fetal and neonatal deaths are analyzed in Table V according to the gestational age; 91 per cent of the neonatal deaths were in the group of preterm infants.

982

Table

August 15, 1975 Am. J. Ohstrt. Gynecol

Ho and Wu

VII.

Causes of death No.

Causes

of

death

Twin

Hyaline membrane disease (HMD) Immaturity alone Necrotizing enterocolitis Asphyxia Septicemia (E. coli) Diaphragmatic hernia

3 1 2 2 0 0

Total number babies

K

of

in the twin of babies 1 (Twin

2 8 3 1 1 1 1

babies Total

deaths

No.

/

11 4 3 3 1 1

% 47.8 17.4, 13.0 13.0 4.4 4.4

15

F

100.0

The neonatal death rate of twin babies delivered by cesarean section was 4 per cent as compared to 7 per cent for those delivered vaginally. Among the 128 twin babies being monitored in the intrapartum period, only five (4 per cent) died in the neonatal period-3 per cent of first twins as compared with 5 per cent of second twins. However, the neonatal death rate of 4 per cent in babies monitored was not statistically significantly lower than the 8.5 per cent for unmonitored babies (p > 0.3). The main causes of death are listed in Table VII. The infants with necrotizing enterocolitis (N.E.C.) and the infant who died of E. coli meningitis also had hyaline membrane disease (H.M.D.) Morbidity. During the study period 51 per cent of the twin babies required admission to the specialcare nursery and 13 per cent were in the intensivecare unit (Table VIII). The neonatal complications of the twin babies are shown in Fig. 1. Out of 105 live-born preterm twin babies, 30 (29 per cent) developed hyaline membrane disease-16 first twins and 14 second twins. All the babies who developed H.M.D. had a gestational age of less than 37 weeks and a birth weight below 2,000 grams. There was no statistically significant difference in the incidence and severity of H.M.D. between the first and second twins. Fortythree per cent were considered to have mild H.M.D., requiring oxygen therapy of not more than 40 per cent; 20 per cent were considered to have moderately severe H.M.D., requiring more than 40 per cent oxygen therapy; the remaining 37 per cent had severe H.M.D., requiring admission to the intensive-care unit and respirator care. Forty-seven per cent of the babies who developed H.M.D. died. Ten per cent of all the twin babies had blood glucose values of less than 40 mg per 100 time during the first 21 hours of life. Only

ml. some nine out

of these 37 babies had blood glucose values below 30 mg. per 100 ml. In 12 per cent of the babies the serum calcium was below 8 mg. per 100 ml. some time before 72 hours of age ; in only 4 per cent was the serum calcium below 7 mg. per 100 ml. In the latter group, 30 per cent were term babies and 70 per cent were preterm babies. Among the babies delivered at term only 2 per cent developed hypocalcemia ; among the preterm babies 8 per cent developed hypocalcemia. Twelve per cent of the babies had serum bilirubin levels more than 10 mg. per 100 ml. some time during the first 3 days of life and 70 per cent of them were L.B.W. babies. Forty-four per cent of them had serum bilirubin levels ranging from 1.5 to 17 mg. per 100 ml. There were no statistical differences in the incidence of hyperbilirubinemia between twin 1 and twin 2. Only seven babies had congenital anomalies detected during their stay in the nursery. Comment

Incidence and race. The incidence of twinning in this series, 1: 112.2 deliveries, was lower than that reported previously (Table IX) .l. ‘{ Since 75 per cent of our hospital population during this period was Mexican-American, the incidence of twinning may well represent the twinning rate of this ethnic Myrianthopoulos’ analyzed 6 15 pairs of group. twins from 56,249 pregnancies. Among this group of mothers, 45 per cent were Caucasians, 47 per cent were black, 7 per cent were Puerto Ricans, and 1 per cent were of other ethnic groups. The incidence of twrinning was found to be highest in blacks (1: 78.8), then Caucasians (1: 100)) and lowest in Puerto Ricans (1: 167) (Table X) In another study”

the

incidence

of twin

pregnancy

in

Orientals

(Chinese and Japanese in California) was also low ( 1: 117 ) . Little is known regarding the incidence of twinning in the Mexican-American population in America. From the present series the twinning rate of Mexican-Americans falls in between that of Caucasians and Orientals. This finding is interesting in view of the fact that Mexican-Americans were thought to have Oriental and Caucasian ancestry. In addition, the statistics from Spain (1967) ’ showed that the twinning rate was 1: 109, which is comparable to the incidence of twinning in the MexicanAmerican population in Los Angeles. The twinning rate in the various age groups was not analyzed, as the majority of mothers in our

Volume 122 Number

Twin

pregnancy

983

8

1

H.M.O. GLUCOSE

c,tJmg’/.

VIII.

Percentage

distribution Total

of Over Twins Twin Twin “I.C.U. tOver

all? (total) 1 2

of neonatal

=

No. babies

19,855 339 171 168 over-all

figure

N.

complications

of the type of neonatal Normal nurseries 91.2 49 52.1 45.9

for all babies

delivered

E.C.

of the twin

care of twin

CONG.MAt

babies.

Numbers

in bars

babies Special ca*e nurseries (To)

term (70)

I.C.U.” 1.9 6.8 4.1 9.5

(166)O (89) (77)

= intensive care unit; Int. C. = intermediate-care all

< 7 mg’l.

SEPSIS

Fig. 1. The percentage incidence indicate percentage of infants.

Table

Ca

Int. (23) (7) (16)

6.9 44.2 43.8 44.6

C.* (150) (75) (75)

Total 8.8 51 47.9 54.1

(173) (82) (91)

nursery. in the hospital.

SNumbers in parentheses indicate number of babies. hospital were young mothers. It has been reported that the incidence of twinning increases with age (up to 35 to 39 years) and parity.“, 4 Obstetric data. The incidence of cephalic presentation-69 per cent for all the twins, 79 per cent for the first twin, and 59 per cent for the second twin-was comparable to that generally reported. Among the group of twins delivered vaginally, 17 per cent of the first twins were delivered by breech as compared to 41 per cent of the second twins; this difference was found to be statistically significant (p < 0.02) and is in agreement with Ferguson’s” finding that the incidence of malpresentation (anything but vertex) in the second

twin was twice as high as that occurring in the first twin. Altogether, 23 per cent of the twin babies were delivered by breech, which was almost 10 times as high as the over-all incidence of 2.4 per cent. A higher percentage of twins requiring midforceps assistance in vaginal delivery was also noted. The over-all incidence of midforceps deliveries in the hospital was 1.5 per cent as compared to 8.8 per cent among twin deliveries. However, there was no difference in the incidence of vacuum extraction either between the first and the second twins or between twins and singletons. The over-all incidence of cesarean section in our

984

Ho and Wu

Am.

Table tl

IX.

I

I 36

WEEKS

I 36

40

Over-all incidence Blacks Caucasians Orientals Puerto Ricans Mexican-Americans

weight ratio for gestational age. The fetal-placental weight ratio for twin pregnancy plotted on Hendrick’s normogram of fetal-placental weight ratio for singleton babies for the various gestational ages. (From Obstet. Gynecol. 24: 357, 1964.)

medical center for the study period was 10 per cent, which was higher than that reported from the other centers.” This might be due to the liberalization of indications for cesarean section for such conditions as premature breech and footling breech presentation. In the present series the cesarean section rate among twin deliveries was 20 per cent as compared to the over-all incidence of cesarean section of 10 per cent. This is in contrast to the report by Guttmacher and Kohl,” who found that the incidence of cesarean section in twins was 5.8 per cent, which was the same as in singletons (5.9 per cent). The time interval between twin births was comparable to the data presented by Bender,’ with 60 per cent of second twins delivering in less than 30 minutes and 3.5 per cent in more than 1 hour. Zygosity. The diagnosis of zygosity of the twins was not available in all instances. However, according to Weinberg’s rule, 61 pairs of twins would be expected to be monozygotic and 116 pairs would be expected to be dizygotic. The accuracy of Weinberg’s rule has been well substantiated by Potter’s” study. Thus the calculated incidence of monozygotic twinning in our Mexican-American population would be 3.1 per 1,000 maternities, which is close to the reported incidence of 3.5 per 1,000 for monozygotic This

series

substantiates

the

idea

that

monozygotic twinning is constant throughout the world without being influenced by race or other factors. Intrapartum fetal monitoring. With the advent of

Incidence 1 : 93.4 1:66 1:85 1:106 1:63.1 1:91.5 1:112

with

reference

I

Incidence

Race

GESTATION

Fig. 2. Fetal-placental

twinning.

I

Table X. Incidence of twinning race in the United States”

(present

15, 1975 Gynecol.

’

Reference

-1SD

34

of twinning”,

Potter et al. (1941) Anderson, W. (1956) Danielson, C. (1960) Aaron et al. (1961) Wynter and Hew (1968) Myrianthopoulos, N. C. (1970) Present series (1974)

rii

I

Incidence

S D

August J. 0hstc.t.

to

1:91:5 1:78:8 1: 100.3 1: 147 1 : 167.1 1:112

series)

intrapartum fetal monitoring and the establishment of the fetal intensive-care unit in the delivery area, almost all high-risk pregnancies delivered at the Los Angeles County-USC Medical Center were monitordd. Data from our obstetric department showed that 18 per cent of all deliveries were monitored in the year 1970. The incidence increased to 25 per cent in 1971, 30 per cent in 1972, and 32 per cent in 1973. During the 24 month study period, 31 per cent of all deliveries were monitored and 36 per cent of twin deliveries were monitored. Since it is the policy to monitor all twins in labor when possible, this low monitoring rate reflects the high incidence of undiagnosed twins in labor. Perhaps more twins would have been diagnosed before delivery if our population had a higher incidence of prenatal care. The neonatal death rate of the twin babies who were being monitored in the intrapartum period was 3.9 per cent (5/l 28)) which was about half of the neonatal death rate of all the twins studied. However, the chi-square distribution test did not show statistical significant difference (p > 0.3) when the neonatal death rates were compared between

the

of twin

babies.

monitored

and

the

unmonitored

groups

Intrauterine growth and fetal-placental weight ratio. Intrauterine growth retardation in twins in late gestation has long been recognized.“-” Of the babies tenth

in this percentile

study, when

uterine

growth

curve.

23.5 per cent were below the plotted on Lubchenco’s intraHowever,

the

weight

distribu-

Volume Numbrr

122 8

tion of the twins in this series falls within the normal distribution of birth weights for twins in Naeye’s intrauterine weight chart for twinslo The fetal-placental weight ratio was analyzed in 78 pairs of twins according to the various gestational ages. Superimposing the present results on Hendrick’s normogram of fetal-placental weight ratio for singleton babies, the fetal-placental weight ratio for twins with gestational ages 32 to 41 weeks was found to be similar to that of singletons (Fig. 2). This finding is in agreement with that reporetd by Naeye.l’ Inadequacy of placental tissue per se as a cause of intrauterine growth retardation appears excluded from the fetal-placental weight ratio. However, a normal fetal-placental weight ratio would not necessarily insure a normal uteroplacental blood flow, especially in late gestation. Relative placental insufficiency in some twin pregnancies may be caused by several factors. Diminished effective uterine wall circulation in late twin pregnancy was reported by Morris and associates.l’ Uterine blood flow is further reduced in hypertensive disease of pregnancy, which is two and a half times as common (21 per cent in twin pregnancy vs. 8 per cent in all pregnancies) in twin pregnancy.“, I3 Unequal distribution of placental mass between the two babies, transplacental vascular anastomosis usually present in monochorionic twins, and the more common occurrences of umbilical cord anomalies and accidents are additional factors causing a higher incidence of intrauterine growth retardation in twin pregnancy. Apgar score. Morbidity as measured by both 1 and 5 minute Apgar scores was significantly higher for the second twin than the first twin (Table III). Second twins had a higher incidence of Apgar score below 7 at both 1 minute (p < 0.001) and 5 minutes (p < 0.01). Th is is in agreement with the findings of Daniels and Hahre.l” Fifty per cent of the twin babies who were delivered by breech (vaginally) had a 1 minute Apgar score of less than 7 and only 31 per cent of the nonbreech babies had a 1 minute Apgar score of less than 7. Thus, babies delivered by breech had a significantly lower 1 minute Apgar score as compared to those nonbreech deliveries (p < 0.001) . Birth weight and gestational age. The over-all incidence of L.B.W. babies in our hospital for the past two years was 8 per cent. The incidence of L.B.W. babies in twin pregnancies was 55 per cent, which is almost seven times higher than the over-all incidence.l* Sixty-four per cent of the twin babies

Twin

Table

XI.

Twin

deaths from reports I

Investigator Bender (1952) Kurtz et al. (1955) Potter (1963) Robertson (1964) Donaldson and Kohl (1965) Hendricks (1966) Myrianthopoulos (1970) Fujikura and Froehlich (1971) Present series (1974)

985

in the literature Deaths

I

1 Tzk!

pregnancy

(95)

1 Fetal

1 ,“,“t”,t

944 1,000 1,134 900

4.0 2.8 3.1 4.4

7n ii 7.5 9.2

11 n

5,282 758 1,230

4.0 8.1

8.9 9.2

12.9 14.0 17.3

1,138 354

5.1 4.2

9.4 6.5

14.5 10.7

1 Total 9.8 10.6 13.6

were delivered at term and 33 per cent of them were preterm babies. The mean length of gestation of twin pregnancy in this series was 36.9 weeks, which is comparable to the 37.1 weeks reported by Guttmacher and Kohl.” Death. Several authors have documented that the neonatal mortality rate of twins is much higher than that of singletons.“, ‘* I’ The fetal and neonatal deaths of twins in the present series (Table VI) amounted to 10.74 per cent whereas the over-all incidence in our hospital was 2.43 per cent for the same time period. The fetal death of twins was more than three times the over-all incidence; and neonatal deaths were six times higher for twins than the over-all incidence. Neonatal deaths in the present study were the lowest compared to the other reported series (Table XI). When subjected to chi-square distribution analysis, the total deaths of the second twin (Table VI) were significantly higher than of the first twin (p < 0.025). This has also been found by other authors.” The incidence of fetal and neonatal deaths is analyzed according to the various gestational ages in Table V. The last column shows a comparison of the percentage of total deaths in the different gestational age groups of the present study to Hendrick’s series. Both series show that the over-all mortality rate of the twin babies delivered prior to 31 weeks of gestation is over 80 per cent. In twins born between 31 and 33 weeks of gestation the mortality rate dropped to about 20 per cent and in those babies born between 34 and 36 weeks of gestation it dropped further to 6 or 7 per cent. As shown in Table VII, prematurity and diseases and complications pertaining to prematurity were the main causes of deaths.

Am.

There was no significant difference in the percentagc* of L.B.W. deaths between the twin babies (12.7 per cent) and the over-all L.B.W. infant population (11.5 per cent). Since L.B.W. twins comprised more than half of all the twin babies, it would be worthwhile to look at the twin deaths with reference to birth weight (Table IV). The last column of Table IV shows the comparison of total deaths (neonatal and fetal death) between twins and the over-all neonatal population. It is evident that the total death rate of twin babies is almost five times as high as that of the over-all population. However, there is no significant difference between twins and the over-all population in the death rate within the various birth weight groups. The present data agree with Potter’s’ findings that the greatly increased mortality rate of twins relates primarily to their increased frequency of prematurity and its complications, rather than to twinning per se. The more liberal use of cesarean section in highrisk pregnancies seemed to help decrease the neonatal mortality rate. Among those 71 babies delivered by cesarean section, three babies died. If the pair of twins who died because of prolapsed cord was excluded there was only one neonatal death in the group of 69 cesarean section babies. Thus, the neonatal death rate of twins delivered by cesarean section (1.45 per cent) was very much lower than the neonatal death rate (6.23 per cent) of noncesarean section twin babies. Morbidity. Because of the high incidence of prematurity in multiple pregnancy,“, ‘. ‘* twins are expected to have more neonatal complications. Almost six times more twin babies required special care than the over-all nursery population (Table III). A significantly larger number of second twins required admission to the intensive-care unit than first twins (p < 0,025). Hyaline membrane disease was the major cause of death in this group of patients. All the babies who developed H.M.D. had a gestational age of less than 37 weeks and a birth weight below 2,000 grams. Seventy per cent (21/30) of the babies who developed H.M.D. had a 1 minute Apgar score of less than 7 and 50 per cent ( 15/30) of the babies who developed H.M.D. had a 5 minute Apgar score of less than 7. As compared to the babies who did not develop H.M.D., babies having H.M.D. had a much higher incidence of Apgar score below 7 at both 1 minute (p < 0.0005) and 5 minutes (p

August J. Obstrt.

15, 1975 Gynecol.

< 0.0005). All the babies who developed necrotizing enterocolitis had H.M.D. The incidence of transient symptomatic neonatal hypoglycemia (i.e., blood glucose value of less than 30 mg. per 100 ml. in term and less than 20 mg. per 100 ml. in preterm infants) for all live births is 0.3 per cent and that of L.B.W. infants is 5.6 per cent. It has been our practice to consider babies with blood glucose levels of less than 40 mg. per 100 ml. as hypoglycemic, and they were treated whether symptomatic or not. By this criterion 10 per cent of the twins had hypoglycemia (Fig. 2). The incidence of hypocalcemia (serum calcium level below 7 mg. per 100 ml.) was 3.7 per cent (13/354) ; 1.7 per cent (4/354) were term babies and 7.8 per cent (g/354) were preterm babies. The incidence of hypocalcemia in preterm babies was significantly higher than that in term babies (p < 0.001 i. This is also true for singleton babies, as reported by Tsang and associates.‘” The incidence of hyperbilirubinemia was not high, and 70 per cent (30/43) was in L.B.W. babies. Thus, the increased morbidity of the twin babies was due to complications of prematurity of the babies rather than to twinning per se. The incidence of congenital malformation among twins in this particular study is only 2 per cent, which is even less than the over-all reported incidence of 3 per cent. It is evident that if prematurity can be prevented, the incidence of neonatal death as well as morbidity can be reduced. An earlier report’” has indicated that ritodrine hydrochloride, a ,&sympathomimetic agent, was successful in arresting premature labor; with this idea in mind, a double-blind study using ritodrine to prevent premature onset of labor in twin pregnancy is currently under way in our medical center. Summary

Previous reports of high morbidity and mortality rates in twin pregnancies involved patients without the benefit of fetal monitoring and neonatal intensive care. The present report involves the 177 pairs of twins born at our institution during the 2 year period from January 1, 1972, to December 31, 1973. The incidence of twinning was 1: 112 deliveries in a population consisting of 76 per cent MexicanAmericans. Intrapartum fetal monitoring was carried out in 36 per cent of deliveries. The incidence of breech delivery was 17 per cent for the first twin and 41 per cent for the second twin. The incidence

Volume Number

of

122 8

Twin

midforceps

sarean

section

occurred

use

was

was

20

in 54 per

weight

infants

cent;

and

tational-age

9 per per

infants

ratio

singletons.

Apgar

scores

were

lower

developed twins.

hyaline cemia

hyaline in

all

51

live

per

at

disease cent),

hyperbilirubinemia The

perinatal

which

was

4.5

times

and

(29

10 mg. mortality higher

in

second was

9 per

per

(4

per rate than

100 was the

recent

were:

cent), ml.

twin

(12

neonatal gestation.

group

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monitored by

per

107/1,000,

twin in

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related premature

is and to

and

of for

rate period

The

reflected morbidity

in rates

morbidity methods reduce

the in and

of

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being

delivered

advances of

death

in

high-risk

improvement this report. for the

37

weight

was or

impact management

prematurity, labor should

who

cent <

by

general

babies

intrapartum

of

death

the

neonatal

of this

previous per

infants

mortality

in those

section.

pregnancies majority

than

987

than

in

incidence

neonatal the

and

lower Ninety-four

occurred

higher

The first

but

pregnancies. The

not

population. the

hospital,

deaths

weeks’

the

cent),

over-all

our

on

mortality

hypoglyper

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hypocalcemia >

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REFERENCES

Infant Death: An Analysis by Maternal Risk and Health Care. Contrasts in Health Status. Vol. I, Report, Health Services Research Study, Institute of Medicine, Washington, D. C., 1973, National Academy of Sciences. 2. Wynter, H. H., and Hew, L. R.: Fetal mortality and morbidity in twin pregnancy, West Indian Med. J. 17: 204, 1968. N. C.: An epidemiologic survey of 3. Myrianthopoulos, twins in a large prospectively studied population, Am. J. Hum. G&et:22: 611, 1970. 4. Dean. G.. and Keane. T.: An investigation of the high ‘twinning rate in’ the Republic of Ireland, Br. J. Prev. Sot. Med. 26: 186, 197’2. 5. Ferguson, W. F.: Perinatal mortality in multiple gestations: A review of perinatal deaths from 1609 multiple gestations, Obstet. Gynecol. 23: 861, 1964. A. F., and Kohl, S. G.: Cesarean section 6. Guttmacher, in twin pregnancy, AM. J. OBSTET. GYNECOL. 83: 866, 196i. S.: Twin megnancv: Review of 472 cases, 7. Bender. J. Obsiet. Gynaecoi. BT. Emp. 59: 510, 1952. 8. Potter, E. L.: Twin zygosity and placental form in relation to the outcome of pregnancy, AM. J, OBSTET. GYNECOL. 87: 566, 1963.

9.

1.

10.

11. 12.

13.

14.

15.

16.

Guttmacher, A. F., and Kohl, S. G.: The fetus of multiple gestations, Obstet. Gynecol. 12: 528, 1958. Naeye, R. L., Benirschke, K., Hagstrom, J. W. C., and Marcus, C. C.: Intrauterine growth of twins as estimated from liveborn birth-weight data, Pediatrics 37: 409, 1966. Naeye, R. L.: The fetal and neonatal development of twins, Pediatrics 33: 546, 1964. Morris, N., Osborn, S. B., and Wright, N. P.: Effective circulation of the uterine wall in later pregnancy measured with “4NaC1, Lancet 1: 323, 1955. Walker, J., and Turnbull, E. P. P.: The environment of the fetus in human multiple pregnancy, Neonatal Studies 4: 123, 1955. Daniels, J. C., and Hahre, F. W.: A retrospective study of 527 twin deliveries, Anesth. Analg. 46: 527, 1967. Tsang, R. C., Light, I. J., Sutherland, J. M., and Kleinman, L. I.: Possible pathogenic factors in neonatal hypocalcemia of prematurity, J. Pediatr. 82: 423. 1973. Wesselius-de Casparis, A., Thiery, M., Yo Le Sian, A.. Baumearten. K.. Brosens, I., Gamisons. 0.. Stalk, J. G., and Vivier, W.: Results of double-blind; multicentre study with ritodrine in premature labour, Br. Med. J. July 17, 1971.